Date   

Re: Shipscatter

Paul Randall G3NJV
 

Hi Phil,  did you ever do HF telephone to Baldock from GBTT?



Sent from my Samsung Galaxy smartphone.



-------- Original message --------
From: Phil Williams <philwill73@...>
Date: 22/05/2020 19:44 (GMT+00:00)
To: UKMicrowaves@groups.io
Subject: [UKMicrowaves] Shipscatter

Further to my earlier one about shipscatter, a dirty great car carrier just went past and its blowing a gale out there too.  This image shows GB3MCB via the ship rolling! I feel sorry for the crew and I know I was a ship R/O on QE2 for years. 



Re: Microwave Modules T432/144R transverter

G8DQX list
 

Martin,

there were at least two variants of that transverter. A PW review (http://www.g4kfk.co.uk/MMT432-144_70cm_Transverter_PW_198111.pdf) indicates that there was the arrangement you noted, to offer double conversion operation. As memory recalls, there was a switch to set 1.6MHz offset operation when required. [My unit was the earlier version that required 1.6MHz offset at 2m, generating RF outside the UK 2m band.]

There was the 432-144R variant, with the 1.6MHz shift, and another 432-144 variant which covered 432-434, plus 432-436. See http://www.wirralcam.org/wadarc/Technical_Topics/MMT432_144.pdf. It is highly likely that other variants exist.

There is a circuit at http://g4fre.com/MM.htm, but it is shows an unswitched LO version. This inside view might also be helpful: http://www.retro.co.za/zs1ke/MMT432-Transverter/index.html.

HTH, 73, Stay Safe,

Robin, G8DQX

PS: Happy days of working PA novices on 70cms FM, sea path!

On 22/05/2020 21:35, g3zqu via groups.io wrote:
Hi all.
I picked up at a rally - remember those! - last year a MM 432/144MHz transverter at a very cheap price!
It has two xtals in it, one at 101MHz and one at 101.4MHz (along with a 116MHz one as well). These will obviously give the needed 1.6MHz shift for repeater operation. Problem is how do you select the appropriate xtal as there are not the usual two toggle switches on the rear over the power DIN socket. However the two DIN pins 2 & 4, normally a "not connected".  are connected to the pcb and I suspect that the repeater shift can be remotely set. The two pins in question have zero volts on one and 8volts on the other.
Question is does anybody know how these pins are connected to remotely control the repeater shift.  As the unit stands with no external connections to either pin,. 144.2MHz in gives 432.2MHz out
Hopefully somebody might know or even have a circuit/manual for this version.

Martin G3ZQU


Re: Microwave Modules T432/144R transverter

Alan Beard
 

Our Mike G4KFK missed one very important Microwave Modules version:

Back in 1977 I had a Yaesu FT-620 6m transceiver, they covered 50 to 54 MHz.
And a Yaesu FT-221.

(Us "Z" call limited licencees had only 50 MHz and up.)

Well, ham satellites were going to use 432 and 435 MHz so I needed a transverter
system that would cover 432 to 436 MHz.

I wrote to Microwave Modules, they responded so I bought their 432 to 50MHz version. 

An FT-620 is extremely easy to hookup to the MMT432-28 (now on 50MHz). In the 620 there's a short
coax from the exciter to the RF PA, route that to a socket on the rear of the radio to feed
the Tx signal to the MMT432. I still have the combo today and it still works.

Thanks MMT.

Alan VK2ZIW


On Fri, 22 May 2020 22:08:11 +0100, chris ruddy via groups.io wrote
> Hopefully this will help you.... http://www.g4kfk.co.uk/html/microwave_modules.html
>  
>  
> Chris MM0KOS
>  
> Sent from Mail for Windows 10
>  

---------------------------------------------------
Alan Beard

OpenWebMail 2.53


Re: Microwave Modules T432/144R transverter

Chris Ruddy MM0KOS
 

Hopefully this will help you.... http://www.g4kfk.co.uk/html/microwave_modules.html

 

 

Chris MM0KOS

 

Sent from Mail for Windows 10

 


Microwave Modules T432/144R transverter

g3zqu
 

Hi all.
I picked up at a rally - remember those! - last year a MM 432/144MHz transverter at a very cheap price!
It has two xtals in it, one at 101MHz and one at 101.4MHz (along with a 116MHz one as well). These will obviously give the needed 1.6MHz shift for repeater operation. Problem is how do you select the appropriate xtal as there are not the usual two toggle switches on the rear over the power DIN socket. However the two DIN pins 2 & 4, normally a "not connected".  are connected to the pcb and I suspect that the repeater shift can be remotely set. The two pins in question have zero volts on one and 8volts on the other.
Question is does anybody know how these pins are connected to remotely control the repeater shift.  As the unit stands with no external connections to either pin,. 144.2MHz in gives 432.2MHz out
Hopefully somebody might know or even have a circuit/manual for this version.

Martin G3ZQU


Re: Shipscatter

Reg Woolley
 

I was on Britannia a few years back and got permission to operate 2m and 70cms. On the way up the north sea not far off the coast. I found the ship to be the best G4SWX notch filter ever invented.  I hasten to add. P and O will no longer tolerate any amateur radio onboard. So dont try.



Reg g8vhi 

Sent from Samsung tablet.


-------- Original message --------
From: Phil Williams <philwill73@...>
Date: 22/05/2020 19:44 (GMT+00:00)
To: UKMicrowaves@groups.io
Subject: [UKMicrowaves] Shipscatter

Further to my earlier one about shipscatter, a dirty great car carrier just went past and its blowing a gale out there too.  This image shows GB3MCB via the ship rolling! I feel sorry for the crew and I know I was a ship R/O on QE2 for years. 



13cm LDMOS amplifiers

Michael Scott
 

Hi all
 
Following the publication of this month’s Scatterpoint, I have had several requests for these amplifiers. Unfortunately we only had nine and they all went very quickly. If anyone wants to pass theirs on to anyone else, a gentle reminder that they were donated to the Group on the understanding that they were not resold, and only shipping costs should be requested.
 
I do still have two similar boards without the LDMOS device on them. They were intended for 2.6 GHz. I have no information on them. They do have circulators fitted to the output, but the rest of the components are presumably bias circuitry etc. The are available free from the Chipbank, but a donation of £5 is requested to cover p&p.
 
A reminder that the Chipbank is open for business. In addition to the amplifiers I have had over forty requests so far this year, but it seems to have gone quiet in the last week or so. There are lots of goodies in the catalogue! I have sussed out how to buy stamps and prepaid labels online so I don’t have to visit the post office either!
 
73, Mike, G3LYP. 


Shipscatter

Phil Williams
 

Further to my earlier one about shipscatter, a dirty great car carrier just went past and its blowing a gale out there too.  This image shows GB3MCB via the ship rolling! I feel sorry for the crew and I know I was a ship R/O on QE2 for years. 



Re: Shipscatter

John E. Beech
 

I remember reading about some one on the south coast who had a hill to the north of him beamed south at ships in the harbour to work anyone north of him.

de John G8SEQ

PS. Not much chance of ship scatter from Coventry, more like flying pig scatter!

-------Original Message-------
From: Phil Williams <philwill73@gmail.com>
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: [UKMicrowaves] Shipscatter
Sent: May 22 '20 10:57

Im near Bude N.Cornwall / Devon border I can normally just see the
Cornish beacon on 23cms with Bodmin Moor in the way but if I beam to
Ireland where I have a sea path I get good reflections of GB3MCB from
ships heading in an out of the Bristol Channel. I'd be interested in
doing a test with shipscatter if anyone else in Cornwall has a
take-off to the north.
Phil G3YPQ


Re: Multiband dish feed

KENT BRITAIN
 

Not sure better, but certainly easier.

On that covers that range is easily available and G4DDK has some in stock.

Cheers Kent

On Friday, May 22, 2020, 12:58:17 AM CDT, Tim <vk2xax@...> wrote:


Wouldn't this range be better served by a Vivaldi ?

cheers

Tim

On 22/5/20 12:31 am, DD1US wrote:
Hi Kent,

Yes, it is a special designed quad logper design. It is difficult to manufacture, especially the broadband balun/matching.

I would like to use it for the frequency range 1.2 GHZ to 10.7 GHz.

Kind regards

Matthias


Von: KENT BRITAIN
Gesendet: Donnerstag, 21. Mai 2020 16:00
Betreff: Re: [UKMicrowaves] Multiband dish feed

The highly compressed quad log periodics?

That has to be a  @$%@%! to build! hihi

What frequency range are you looking at?

Kent

On Thursday, May 21, 2020, 8:28:18 AM CDT, DD1US <matthias.bopp@...> wrote:


Hi Kent,

 

Thank you very much.

 

I just wanted to make sure that my thought process is right and I am not wasting time in trying to build a system around such a feed.

 

The concept with the stepped ground plane is interesting however your experiment with the thermal sensitive plastic suggests, that
it might now be very successful
😉

 

I am kind of searching of the holy grail of a broadband feed for a dish … not for professional use just for my hobby and presently the

“eleven feed” seems to come quite close … have you looked into that ?

 

Kind regards

 

Matthias

 

www.dd1us.de

 

 

Von: UKMicrowaves@groups.io <UKMicrowaves@groups.io> Im Auftrag von KENT BRITAIN
Gesendet: Donnerstag, 21. Mai 2020 15:14
An: UKMicrowaves@groups.io; UKMicrowaves@groups.io
Betreff: Re: [UKMicrowaves] Multiband dish feed

 

Hi Matt

 

You are quite correct, your LNA will never see cold sky with a log spiral feed.

Virtually all the Log Spirals are used in Electronic Warfare, most commonly

on aircraft to detect radar signals.   Those are very high power pulses

so the low gain and high noise temperature are not an issue.

 

There are techniques where a stepped ground plane is put behind the

spiral instead of absorber.  But you have to know a lot about the radiation

off your spiral to properly design that stepped ground plane.

 

Yeas ago I watched an interesting demonstration with a log spiral.

They used a thin sheet of thermal sensitive plastic.  The stuff that just

the heat of your hand would make it change colour.  We put that plastic

over the spiral and feed just over a watt of RF into it.  You saw colour

changes at the active area of the antenna.  Then we slowly swept frequency. 

The active areas jumped all over the place.     It was NOT a

smooth transition from the center to the

outer parts of the spiral.   The RF always from a spot to resonate, but

there was no logic to the pattern changes.

 

On the BIG dishes  ( 30+ meters) they like to use a Ridged Horn when they need a

broad band feed.   I like to think of a Vivaldi antenna as a ridged horn

without the horn.    The vivaldi is also used as a dish feed on several military

ELINT systems.     I hope this helps    Kent

 

On Thursday, May 21, 2020, 1:41:16 AM CDT, DD1US <matthias.bopp@...> wrote:

 

 

Hi Kent and John,

 

Thank you very much for this interesting discussion.

 

I have a question related to such a cavity backed spiral log periodic antenna:

 

I would like to use such an antenna as a feed in a parabolic dish, especially for satellite communication.

 

For TX half the power is lost in the absorber material of the cavity, which might be acceptable in my applications.
However, I have to see what the maximum power will be, which I can use, as the absorber material will get apparently hot
at higher power.

 

For RX my understanding is, that the absorber material is warm, let assume at ambient temperature, and thus radiates
a lot of thermal noise which is received by the spiral antenna. This noise will completely ruin the G/T and I will not be
able to receive weak satellite signals which is possible with other antennas as the background noise in the cold sky is low.

 

Maybe the same cavity backed spiral feed mounted in a dish “on the satellite” which is pointed to Earth might work,
as the feed is quite cold (when not exposed to the sun) and the background noise received by the dish is the warm Earth anyway.

 

Is my understanding correct which means there is no point in using such a cavity backed spiral log periodic feed for a satellite

groundstation ?

 

Many thanks in advance for your feedback.

 

Kind regards

 

Matthias

 

www.dd1us.de

 

 

 

 

Von: UKMicrowaves@groups.io <UKMicrowaves@groups.io> Im Auftrag von KENT BRITAIN
Gesendet: Donnerstag, 21. Mai 2020 02:47
An: UKMicrowaves@groups.io; ukmicrowaves@groups.io
Betreff: Re: [UKMicrowaves] Multiband dish feed

 

Hi John

 

With an LP feed you adjust the feed for best performance on the highest

frequency of interest.

 

On Lower frequencies the phase center does move a bit, but since the

waves are longer, phase error is quite minor.

 

I'm afraid your Log Spiral disk does indeed effectively change phase center as

you go down in frequency.   In contrast to the Log Periodic, the spiral

appears to move closer to the dish as your wavelength increases.

I have produced hundreds for various clients, but due to the absorber

in the cavity, typical gain is in the -6 to -8 dBi range.

 

These use 'Infinity Baluns" to take 50 Ohms to 200 Ohms balanced.

They run from the back of the cavity to the center of the spirals.

 

These are used as my Left/Right CP references on the antenna range.

One of these (They made their own cavity!) is currently in orbit.

 

Kent WA5VJB/G8EMY  (Yea, an 8, but a full license)

 

 

 

On Wednesday, May 20, 2020, 4:30:21 PM CDT, John E. Beech <john@...> wrote:

 

 

Isn't variable illumination a feature of all multiband feeds? If you use a log periodic the phase centre shifts, so the illumination alters. If you use a horn, the gain of the horn increases with frequency. The brief look I've had at dual band feeds have more gain & therefore different illumination at the higher frequency.
          I do have a log periodic antenna designed to work at UHF/SHF in which the phase centre does NOT change with frequency. It consists of two intertwined spirals, fed at the centre. But there is a snag or two. I used to use them professionally at 888 MHz. It was a design I inherited from a previous designer (unknown). They give a circularly polarised signal & their feed impedance is 188.4 ohms. This means throwing away 3 dB of gain unless you can persuade the receiving station to operate circularly polarization & practically you need to be able to switch from RHC to LHC 'cos if you get it wrong then received signal is practically zilch! Normally used in a cavity their impedance drops to 100 - 150 ohms. Not sure what happens if you fit them at the focal plane of a dish, but I can give it a go - it will give me something to measure with my new toy - a NanoVNA. My particular antennas are about  6 in (25 cm) diameter printed on FR4 Cu, tinned. They SHOULD work from about 500 MHz to 30 GHz, but I'm not sure what the tin-lead coating does at the higher frequencies. The half power beam width appears to stay constant irrespective of frequency at between 70 & 90 deg.
          It might be possible to control the impedance to some extent by using a splash plate reflector in a dish application. If I can get it down to 100 ohms then matching is relatively straightforward using a quarter wave transformer.

See here:  http://www.antenna-theory.com/antennas/travelling/spiral.php

de John G8SEQ

>  -------Original Message-------
>  From: Andy G4JNT <andy.g4jnt@...>
>  To: UK Microwaves groups.io <UKMicrowaves@groups.io>
>  Subject: Re: [UKMicrowaves] Multiband dish feed
>  Sent: May 20 '20 20:58

>  Just a thought.
>  Does a wideband antenna like a Vivaldi illuminating a dish lead to a
>  roughly constant gain? As freq increases, beamwidth of the feed goes
>  down, illuminating less of the dish leading to reduced gain.

>  Intuition says constant gain could be the result.

>  Andy
www.g4jnt.com

>  On Wed, 20 May 2020 at 20:54, KENT BRITAIN <WA5VJB@...> wrote:

>  > The 1.5-15 GHz Vivaldi will take that easily.
>  >
>  > On Wednesday, May 20, 2020, 2:46:57 PM CDT, Noel G8GTZ
>  > <noel@...> wrote:
>  >
>  > Oh not QRO! Typically 25 watts on 2.3 and 10 watts on 3.4, 5.6 and
>  > 10GHz - all DATV so long duty cycle compared to SSB.
>  >
>  > Noel



-- 
VK2XAX : QF56if : ITU59 : CQ30 : BMARC : WIA


Shipscatter

Phil Williams
 

Im near Bude N.Cornwall / Devon border I can normally just see the Cornish beacon on 23cms with Bodmin Moor in the way but if I beam to Ireland where I have a sea path I get good reflections of GB3MCB from ships heading in an out of the Bristol Channel. I'd be interested in doing a test with shipscatter if anyone else in Cornwall has a take-off to the north.
Phil G3YPQ 


Let Us Know Who You Are - Check Your Profile

Andy G4JNT
 

Good morning:
Over recent weeks we've had quite a few new members to these two groups, but several of you are joining-up with somewhat meaningless or anonymised names.

Can you please adopt a user name or profile that ideally includes your callsign - if you have one - or at least a name that distinguishes. 

For both groups I've reduced the number of moderated posts needed from new members to one, and usually waive that straightaway .  Especially as we seem to have now got-rid of the troublesome persons that  appeared on both groups.


Andy   G4JNT
Group Owner


Re: Multiband dish feed

DD1US
 

Hi Tim,

 

Quite possible, however I would like to have circular polarization and a pattern which fits a prime focus dish with an f/D=0.4.

 

Kind regards

 

Matthias

 

www.dd1us.de

 

 

Von: UKMicrowaves@groups.io <UKMicrowaves@groups.io> Im Auftrag von Tim
Gesendet: Freitag, 22. Mai 2020 07:58
An: UKMicrowaves@groups.io
Betreff: Re: [UKMicrowaves] Multiband dish feed

 

Wouldn't this range be better served by a Vivaldi ?

cheers

Tim

On 22/5/20 12:31 am, DD1US wrote:

Hi Kent,

 

Yes, it is a special designed quad logper design. It is difficult to manufacture, especially the broadband balun/matching.

 

I would like to use it for the frequency range 1.2 GHZ to 10.7 GHz.

 

Kind regards

 

Matthias

 

 

Von: KENT BRITAIN

Gesendet: Donnerstag, 21. Mai 2020 16:00

Betreff: Re: [UKMicrowaves] Multiband dish feed

 

The highly compressed quad log periodics?

 

That has to be a  @$%@%! to build! hihi

 

What frequency range are you looking at?

 

Kent

 

On Thursday, May 21, 2020, 8:28:18 AM CDT, DD1US <matthias.bopp@...> wrote:

 

 

Hi Kent,

 

Thank you very much.

 

I just wanted to make sure that my thought process is right and I am not wasting time in trying to build a system around such a feed.

 

The concept with the stepped ground plane is interesting however your experiment with the thermal sensitive plastic suggests, that
it might now be very successful
😉

 

I am kind of searching of the holy grail of a broadband feed for a dish … not for professional use just for my hobby and presently the

“eleven feed” seems to come quite close … have you looked into that ?

 

Kind regards

 

Matthias

 

www.dd1us.de

 

 

Von: UKMicrowaves@groups.io <UKMicrowaves@groups.io> Im Auftrag von KENT BRITAIN
Gesendet: Donnerstag, 21. Mai 2020 15:14
An: UKMicrowaves@groups.io; UKMicrowaves@groups.io
Betreff: Re: [UKMicrowaves] Multiband dish feed

 

Hi Matt

 

You are quite correct, your LNA will never see cold sky with a log spiral feed.

Virtually all the Log Spirals are used in Electronic Warfare, most commonly

on aircraft to detect radar signals.   Those are very high power pulses

so the low gain and high noise temperature are not an issue.

 

There are techniques where a stepped ground plane is put behind the

spiral instead of absorber.  But you have to know a lot about the radiation

off your spiral to properly design that stepped ground plane.

 

Yeas ago I watched an interesting demonstration with a log spiral.

They used a thin sheet of thermal sensitive plastic.  The stuff that just

the heat of your hand would make it change colour.  We put that plastic

over the spiral and feed just over a watt of RF into it.  You saw colour

changes at the active area of the antenna.  Then we slowly swept frequency. 

The active areas jumped all over the place.     It was NOT a

smooth transition from the center to the

outer parts of the spiral.   The RF always from a spot to resonate, but

there was no logic to the pattern changes.

 

On the BIG dishes  ( 30+ meters) they like to use a Ridged Horn when they need a

broad band feed.   I like to think of a Vivaldi antenna as a ridged horn

without the horn.    The vivaldi is also used as a dish feed on several military

ELINT systems.     I hope this helps    Kent

 

On Thursday, May 21, 2020, 1:41:16 AM CDT, DD1US <matthias.bopp@...> wrote:

 

 

Hi Kent and John,

 

Thank you very much for this interesting discussion.

 

I have a question related to such a cavity backed spiral log periodic antenna:

 

I would like to use such an antenna as a feed in a parabolic dish, especially for satellite communication.

 

For TX half the power is lost in the absorber material of the cavity, which might be acceptable in my applications.
However, I have to see what the maximum power will be, which I can use, as the absorber material will get apparently hot
at higher power.

 

For RX my understanding is, that the absorber material is warm, let assume at ambient temperature, and thus radiates
a lot of thermal noise which is received by the spiral antenna. This noise will completely ruin the G/T and I will not be
able to receive weak satellite signals which is possible with other antennas as the background noise in the cold sky is low.

 

Maybe the same cavity backed spiral feed mounted in a dish “on the satellite” which is pointed to Earth might work,
as the feed is quite cold (when not exposed to the sun) and the background noise received by the dish is the warm Earth anyway.

 

Is my understanding correct which means there is no point in using such a cavity backed spiral log periodic feed for a satellite

groundstation ?

 

Many thanks in advance for your feedback.

 

Kind regards

 

Matthias

 

www.dd1us.de

 

 

 

 

Von: UKMicrowaves@groups.io <UKMicrowaves@groups.io> Im Auftrag von KENT BRITAIN
Gesendet: Donnerstag, 21. Mai 2020 02:47
An: UKMicrowaves@groups.io; ukmicrowaves@groups.io
Betreff: Re: [UKMicrowaves] Multiband dish feed

 

Hi John

 

With an LP feed you adjust the feed for best performance on the highest

frequency of interest.

 

On Lower frequencies the phase center does move a bit, but since the

waves are longer, phase error is quite minor.

 

I'm afraid your Log Spiral disk does indeed effectively change phase center as

you go down in frequency.   In contrast to the Log Periodic, the spiral

appears to move closer to the dish as your wavelength increases.

I have produced hundreds for various clients, but due to the absorber

in the cavity, typical gain is in the -6 to -8 dBi range.

 

These use 'Infinity Baluns" to take 50 Ohms to 200 Ohms balanced.

They run from the back of the cavity to the center of the spirals.

 

These are used as my Left/Right CP references on the antenna range.

One of these (They made their own cavity!) is currently in orbit.

 

Kent WA5VJB/G8EMY  (Yea, an 8, but a full license)

 

 

 

On Wednesday, May 20, 2020, 4:30:21 PM CDT, John E. Beech <john@...> wrote:

 

 

Isn't variable illumination a feature of all multiband feeds? If you use a log periodic the phase centre shifts, so the illumination alters. If you use a horn, the gain of the horn increases with frequency. The brief look I've had at dual band feeds have more gain & therefore different illumination at the higher frequency.
          I do have a log periodic antenna designed to work at UHF/SHF in which the phase centre does NOT change with frequency. It consists of two intertwined spirals, fed at the centre. But there is a snag or two. I used to use them professionally at 888 MHz. It was a design I inherited from a previous designer (unknown). They give a circularly polarised signal & their feed impedance is 188.4 ohms. This means throwing away 3 dB of gain unless you can persuade the receiving station to operate circularly polarization & practically you need to be able to switch from RHC to LHC 'cos if you get it wrong then received signal is practically zilch! Normally used in a cavity their impedance drops to 100 - 150 ohms. Not sure what happens if you fit them at the focal plane of a dish, but I can give it a go - it will give me something to measure with my new toy - a NanoVNA. My particular antennas are about  6 in (25 cm) diameter printed on FR4 Cu, tinned. They SHOULD work from about 500 MHz to 30 GHz, but I'm not sure what the tin-lead coating does at the higher frequencies. The half power beam width appears to stay constant irrespective of frequency at between 70 & 90 deg.
          It might be possible to control the impedance to some extent by using a splash plate reflector in a dish application. If I can get it down to 100 ohms then matching is relatively straightforward using a quarter wave transformer.

See here:  http://www.antenna-theory.com/antennas/travelling/spiral.php

de John G8SEQ

>  -------Original Message-------
>  From: Andy G4JNT <andy.g4jnt@...>
>  To: UK Microwaves groups.io <UKMicrowaves@groups.io>
>  Subject: Re: [UKMicrowaves] Multiband dish feed
>  Sent: May 20 '20 20:58

>  Just a thought.
>  Does a wideband antenna like a Vivaldi illuminating a dish lead to a
>  roughly constant gain? As freq increases, beamwidth of the feed goes
>  down, illuminating less of the dish leading to reduced gain.

>  Intuition says constant gain could be the result.

>  Andy
www.g4jnt.com

>  On Wed, 20 May 2020 at 20:54, KENT BRITAIN <WA5VJB@...> wrote:

>  > The 1.5-15 GHz Vivaldi will take that easily.
>  >
>  > On Wednesday, May 20, 2020, 2:46:57 PM CDT, Noel G8GTZ
>  > <noel@...> wrote:
>  >
>  > Oh not QRO! Typically 25 watts on 2.3 and 10 watts on 3.4, 5.6 and
>  > 10GHz - all DATV so long duty cycle compared to SSB.
>  >
>  > Noel

-- 
VK2XAX : QF56if : ITU59 : CQ30 : BMARC : WIA


Re: Multiband dish feed

Tim, VK2XAX
 

Wouldn't this range be better served by a Vivaldi ?

cheers

Tim

On 22/5/20 12:31 am, DD1US wrote:
Hi Kent,

Yes, it is a special designed quad logper design. It is difficult to manufacture, especially the broadband balun/matching.

I would like to use it for the frequency range 1.2 GHZ to 10.7 GHz.

Kind regards

Matthias


Von: KENT BRITAIN
Gesendet: Donnerstag, 21. Mai 2020 16:00
Betreff: Re: [UKMicrowaves] Multiband dish feed

The highly compressed quad log periodics?

That has to be a  @$%@%! to build! hihi

What frequency range are you looking at?

Kent

On Thursday, May 21, 2020, 8:28:18 AM CDT, DD1US <matthias.bopp@...> wrote:


Hi Kent,

 

Thank you very much.

 

I just wanted to make sure that my thought process is right and I am not wasting time in trying to build a system around such a feed.

 

The concept with the stepped ground plane is interesting however your experiment with the thermal sensitive plastic suggests, that
it might now be very successful
😉

 

I am kind of searching of the holy grail of a broadband feed for a dish … not for professional use just for my hobby and presently the

“eleven feed” seems to come quite close … have you looked into that ?

 

Kind regards

 

Matthias

 

www.dd1us.de

 

 

Von: UKMicrowaves@groups.io <UKMicrowaves@groups.io> Im Auftrag von KENT BRITAIN
Gesendet: Donnerstag, 21. Mai 2020 15:14
An: UKMicrowaves@groups.io; UKMicrowaves@groups.io
Betreff: Re: [UKMicrowaves] Multiband dish feed

 

Hi Matt

 

You are quite correct, your LNA will never see cold sky with a log spiral feed.

Virtually all the Log Spirals are used in Electronic Warfare, most commonly

on aircraft to detect radar signals.   Those are very high power pulses

so the low gain and high noise temperature are not an issue.

 

There are techniques where a stepped ground plane is put behind the

spiral instead of absorber.  But you have to know a lot about the radiation

off your spiral to properly design that stepped ground plane.

 

Yeas ago I watched an interesting demonstration with a log spiral.

They used a thin sheet of thermal sensitive plastic.  The stuff that just

the heat of your hand would make it change colour.  We put that plastic

over the spiral and feed just over a watt of RF into it.  You saw colour

changes at the active area of the antenna.  Then we slowly swept frequency. 

The active areas jumped all over the place.     It was NOT a

smooth transition from the center to the

outer parts of the spiral.   The RF always from a spot to resonate, but

there was no logic to the pattern changes.

 

On the BIG dishes  ( 30+ meters) they like to use a Ridged Horn when they need a

broad band feed.   I like to think of a Vivaldi antenna as a ridged horn

without the horn.    The vivaldi is also used as a dish feed on several military

ELINT systems.     I hope this helps    Kent

 

On Thursday, May 21, 2020, 1:41:16 AM CDT, DD1US <matthias.bopp@...> wrote:

 

 

Hi Kent and John,

 

Thank you very much for this interesting discussion.

 

I have a question related to such a cavity backed spiral log periodic antenna:

 

I would like to use such an antenna as a feed in a parabolic dish, especially for satellite communication.

 

For TX half the power is lost in the absorber material of the cavity, which might be acceptable in my applications.
However, I have to see what the maximum power will be, which I can use, as the absorber material will get apparently hot
at higher power.

 

For RX my understanding is, that the absorber material is warm, let assume at ambient temperature, and thus radiates
a lot of thermal noise which is received by the spiral antenna. This noise will completely ruin the G/T and I will not be
able to receive weak satellite signals which is possible with other antennas as the background noise in the cold sky is low.

 

Maybe the same cavity backed spiral feed mounted in a dish “on the satellite” which is pointed to Earth might work,
as the feed is quite cold (when not exposed to the sun) and the background noise received by the dish is the warm Earth anyway.

 

Is my understanding correct which means there is no point in using such a cavity backed spiral log periodic feed for a satellite

groundstation ?

 

Many thanks in advance for your feedback.

 

Kind regards

 

Matthias

 

www.dd1us.de

 

 

 

 

Von: UKMicrowaves@groups.io <UKMicrowaves@groups.io> Im Auftrag von KENT BRITAIN
Gesendet: Donnerstag, 21. Mai 2020 02:47
An: UKMicrowaves@groups.io; ukmicrowaves@groups.io
Betreff: Re: [UKMicrowaves] Multiband dish feed

 

Hi John

 

With an LP feed you adjust the feed for best performance on the highest

frequency of interest.

 

On Lower frequencies the phase center does move a bit, but since the

waves are longer, phase error is quite minor.

 

I'm afraid your Log Spiral disk does indeed effectively change phase center as

you go down in frequency.   In contrast to the Log Periodic, the spiral

appears to move closer to the dish as your wavelength increases.

I have produced hundreds for various clients, but due to the absorber

in the cavity, typical gain is in the -6 to -8 dBi range.

 

These use 'Infinity Baluns" to take 50 Ohms to 200 Ohms balanced.

They run from the back of the cavity to the center of the spirals.

 

These are used as my Left/Right CP references on the antenna range.

One of these (They made their own cavity!) is currently in orbit.

 

Kent WA5VJB/G8EMY  (Yea, an 8, but a full license)

 

 

 

On Wednesday, May 20, 2020, 4:30:21 PM CDT, John E. Beech <john@...> wrote:

 

 

Isn't variable illumination a feature of all multiband feeds? If you use a log periodic the phase centre shifts, so the illumination alters. If you use a horn, the gain of the horn increases with frequency. The brief look I've had at dual band feeds have more gain & therefore different illumination at the higher frequency.
          I do have a log periodic antenna designed to work at UHF/SHF in which the phase centre does NOT change with frequency. It consists of two intertwined spirals, fed at the centre. But there is a snag or two. I used to use them professionally at 888 MHz. It was a design I inherited from a previous designer (unknown). They give a circularly polarised signal & their feed impedance is 188.4 ohms. This means throwing away 3 dB of gain unless you can persuade the receiving station to operate circularly polarization & practically you need to be able to switch from RHC to LHC 'cos if you get it wrong then received signal is practically zilch! Normally used in a cavity their impedance drops to 100 - 150 ohms. Not sure what happens if you fit them at the focal plane of a dish, but I can give it a go - it will give me something to measure with my new toy - a NanoVNA. My particular antennas are about  6 in (25 cm) diameter printed on FR4 Cu, tinned. They SHOULD work from about 500 MHz to 30 GHz, but I'm not sure what the tin-lead coating does at the higher frequencies. The half power beam width appears to stay constant irrespective of frequency at between 70 & 90 deg.
          It might be possible to control the impedance to some extent by using a splash plate reflector in a dish application. If I can get it down to 100 ohms then matching is relatively straightforward using a quarter wave transformer.

See here:  http://www.antenna-theory.com/antennas/travelling/spiral.php

de John G8SEQ

>  -------Original Message-------
>  From: Andy G4JNT <andy.g4jnt@...>
>  To: UK Microwaves groups.io <UKMicrowaves@groups.io>
>  Subject: Re: [UKMicrowaves] Multiband dish feed
>  Sent: May 20 '20 20:58

>  Just a thought.
>  Does a wideband antenna like a Vivaldi illuminating a dish lead to a
>  roughly constant gain? As freq increases, beamwidth of the feed goes
>  down, illuminating less of the dish leading to reduced gain.

>  Intuition says constant gain could be the result.

>  Andy
www.g4jnt.com

>  On Wed, 20 May 2020 at 20:54, KENT BRITAIN <WA5VJB@...> wrote:

>  > The 1.5-15 GHz Vivaldi will take that easily.
>  >
>  > On Wednesday, May 20, 2020, 2:46:57 PM CDT, Noel G8GTZ
>  > <noel@...> wrote:
>  >
>  > Oh not QRO! Typically 25 watts on 2.3 and 10 watts on 3.4, 5.6 and
>  > 10GHz - all DATV so long duty cycle compared to SSB.
>  >
>  > Noel



-- 
VK2XAX : QF56if : ITU59 : CQ30 : BMARC : WIA


Re: Multiband dish feed

Alan Beard
 

When you want all polarisations from the antenna and 10% at least bandwidth,

Check my picture, a 1296 MHz dish feed, along with a quadrature 90 deg. hybrid, 
horizontal, vertical, circular both RH and LH are covered.

Alan VK2ZIW

On Thu, 21 May 2020 18:59:51 +0000 (UTC), KENT BRITAIN wrote
> Yes, with care you might get the odd harmonics to line up.
>
> GOOD LUCK!
>
> (Working on some crossed Vivaldis for 2 clients.
>   Hard to get the feedlines to cross and not interact though)
>
> On Thursday, May 21, 2020, 1:53:07 PM CDT, John E. Beech <john@...> wrote:
>
> Hi Kent,
            Thanks for the explanation. I can see what is happening now. I'll try mine as it might be a neater solution  than what I have previously used. I'm not interested in multiband but I am interested in producing circular polarization.
        One point, won't the ripples be harmonically related? If so it might not be such a had option for amateur bands.

de John G8SEQ

>  -------Original Message-------
>  From: KENT BRITAIN <WA5VJB@...>
>  To: UKMicrowaves@groups.io <ukmicrowaves@groups.io>, ukmicrowaves@groups.io <ukmicrowaves@groups.io>
>  Subject: Re: [UKMicrowaves] Multiband dish feed
>  Sent: May 21 '20 14:57

>  If you mount the spiral such the focus of the dish it on the center of
>  the
>  spiral. You are well focused for high frequency range of the spiral.

>  But at lower frequencies the radiation tends to be from the outer
>  edges
>  of the spiral. Outside the focus area of the dish. With a BIG dish
>  this is less of a problem, or if the spiral is only used over a narrow
>  range

>  The problem with a simple ground plane behind the spiral is that works

>  best at about 1/4 wavelength. When the spiral is working over a 10 to
>  1
>  frequency range, that 1/4 wavelength is only on 1 frequency.
>  The antenna will have massive ripples in gain and impedance
>  when you sweep frequency.

>  I have used a commercial log spiral as a dish feed years ago.
>  It worked, it wouldn't say it worked well. Today I use either an
>  LP or a Vivaldi when I need a broad band feed.

>  Kent

>  On Thursday, May 21, 2020, 2:54:39 AM CDT, John E. Beech
>  <john@...> wrote:

>  Hi Kent,
>  I don't understand why the phase centre changes with the spiral
>  antenna as a dish feed. Do you have any mathematical reasoning/formula
>  to back this up?
>  Also I wasn't considering using a spiral mounted in a cavity for the
>  feed. My idea is to use a circular plane reflector ( splash plate),
>  positioned to adjust the feed point impedance to around 100 ohms. As
>  it stands the spiral antenna is bidirectional, like any other dipole,
>  but the phase of the radiation is different by 180 deg or put another
>  way , the front face of the spiral emits RHC while the rear face emits
>  LHC. Refelection from the dish reverses the phase so only RHC is
>  radiated in the forward direction from the dish. If a splash plate is
>  now introduced, this reflector reverses the phase and sends it back
>  towards the spiral and the dish such that it is now LHC ie in phase.
>  Again all the forward radiation is RHC. There is a slight loss of gain
>  due to the reflector/spiral assembly masking part of the dish, but
>  this is minimal provided the dish diameter is large compared to the
>  feed point diameter ( which it normally is ).
>  This type of feed should have a gain of 2-3 dB over a bare spiral,
>  which will reduce the illumination angle from 90 to 70 deg down to
>  something like 70 - 50 deg. Obviously you would need to choose the
>  dish f/D ratio to suit this angle for best performance.

>  de John G8SEQ

>  > -------Original Message-------
>  > From: KENT BRITAIN <WA5VJB@...>
>  > To: UKMicrowaves@groups.io <ukmicrowaves@groups.io>,
ukmicrowaves@groups.io <ukmicrowaves@groups.io>
>  > Subject: Re: [UKMicrowaves] Multiband dish feed
>  > Sent: May 21 '20 01:47
>  >
>  > Hi John
>  >
>  > With an LP feed you adjust the feed for best performance on the
>  > highest
>  > frequency of interest.
>  >
>  > On Lower frequencies the phase center does move a bit, but since
>  the
>  > waves are longer, phase error is quite minor.
>  >
>  > I'm afraid your Log Spiral disk does indeed effectively change
>  phase
>  > center as
>  > you go down in frequency. In contrast to the Log Periodic, the
>  spiral
>  > appears to move closer to the dish as your wavelength increases.
>  > I have produced hundreds for various clients, but due to the
>  absorber
>  > in the cavity, typical gain is in the -6 to -8 dBi range.
>  >
>  > These use 'Infinity Baluns" to take 50 Ohms to 200 Ohms balanced.
>  > They run from the back of the cavity to the center of the spirals.
>  >
>  > These are used as my Left/Right CP references on the antenna range.
>  > One of these (They made their own cavity!) is currently in orbit.
>  >
>  > Kent WA5VJB/G8EMY (Yea, an 8, but a full license)
>  >
>  > On Wednesday, May 20, 2020, 4:30:21 PM CDT, John E. Beech
>  > <john@...> wrote:
>  >
>  > Isn't variable illumination a feature of all multiband feeds? If
>  you
>  > use a log periodic the phase centre shifts, so the illumination
>  > alters. If you use a horn, the gain of the horn increases with
>  > frequency. The brief look I've had at dual band feeds have more
>  gain &
>  > therefore different illumination at the higher frequency.
>  > I do have a log periodic antenna designed to work at UHF/SHF in
>  which
>  > the phase centre does NOT change with frequency. It consists of two
>  > intertwined spirals, fed at the centre. But there is a snag or two.
>  I
>  > used to use them professionally at 888 MHz. It was a design I
>  > inherited from a previous designer (unknown). They give a
>  circularly
>  > polarised signal & their feed impedance is 188.4 ohms. This means
>  > throwing away 3 dB of gain unless you can persuade the receiving
>  > station to operate circularly polarization & practically you need
>  to
>  > be able to switch from RHC to LHC 'cos if you get it wrong then
>  > received signal is practically zilch! Normally used in a cavity
>  their
>  > impedance drops to 100 - 150 ohms. Not sure what happens if you fit
>  > them at the focal plane of a dish, but I can give it a go - it will
>  > give me something to measure with my new toy - a NanoVNA. My
>  > particular antennas are about 6 in (25 cm) diameter printed on FR4
>  Cu,
>  > tinned. They SHOULD work from about 500 MHz to 30 GHz, but I'm not
>  > sure what the tin-lead coating does at the higher frequencies. The
>  > half power beam width appears to stay constant irrespective of
>  > frequency at between 70 & 90 deg.
>  > It might be possible to control the impedance to some extent by
>  using
>  > a splash plate reflector in a dish application. If I can get it
>  down
>  > to 100 ohms then matching is relatively straightforward using a
>  > quarter wave transformer.
>  >
>  > See here:
>  > http://www.antenna-theory.com/antennas/travelling/spiral.php
>  >
>  > de John G8SEQ
>  >
>  > > -------Original Message-------
>  > > From: Andy G4JNT <andy.g4jnt@...>
>  > > To: UK Microwaves groups.io <UKMicrowaves@groups.io>
>  > > Subject: Re: [UKMicrowaves] Multiband dish feed
>  > > Sent: May 20 '20 20:58
>  > >
>  > > Just a thought.
>  > > Does a wideband antenna like a Vivaldi illuminating a dish lead
>  to
>  > a
>  > > roughly constant gain? As freq increases, beamwidth of the feed
>  > goes
>  > > down, illuminating less of the dish leading to reduced gain.
>  > >
>  > > Intuition says constant gain could be the result.
>  > >
>  > > Andy
>  > > www.g4jnt.com
>  > >
>  > > On Wed, 20 May 2020 at 20:54, KENT BRITAIN <WA5VJB@...>
>  > wrote:
>  > >
>  > > > The 1.5-15 GHz Vivaldi will take that easily.
>  > > >
>  > > > On Wednesday, May 20, 2020, 2:46:57 PM CDT, Noel G8GTZ
>  > > > <noel@...> wrote:
>  > > >
>  > > > Oh not QRO! Typically 25 watts on 2.3 and 10 watts on 3.4, 5.6
>  > and
>  > > > 10GHz - all DATV so long duty cycle compared to SSB.
>  > > >
>  > > > Noel
>  > >
>  > >
>  >
>  >







---------------------------------------------------
Alan Beard

OpenWebMail 2.53


Re: Multiband dish feed

KENT BRITAIN
 

Yes, with care you might get the odd harmonics to line up.

GOOD LUCK!

(Working on some crossed Vivaldis for 2 clients.
  Hard to get the feedlines to cross and not interact though)

On Thursday, May 21, 2020, 1:53:07 PM CDT, John E. Beech <john@...> wrote:


Hi Kent,
            Thanks for the explanation. I can see what is happening now. I'll try mine as it might be a neater solution  than what I have previously used. I'm not interested in multiband but I am interested in producing circular polarization.
        One point, won't the ripples be harmonically related? If so it might not be such a had option for amateur bands.

de John G8SEQ

>  -------Original Message-------
>  From: KENT BRITAIN <WA5VJB@...>
>  To: UKMicrowaves@groups.io <ukmicrowaves@groups.io>, ukmicrowaves@groups.io <ukmicrowaves@groups.io>
>  Subject: Re: [UKMicrowaves] Multiband dish feed
>  Sent: May 21 '20 14:57

>  If you mount the spiral such the focus of the dish it on the center of
>  the
>  spiral. You are well focused for high frequency range of the spiral.

>  But at lower frequencies the radiation tends to be from the outer
>  edges
>  of the spiral. Outside the focus area of the dish. With a BIG dish
>  this is less of a problem, or if the spiral is only used over a narrow
>  range

>  The problem with a simple ground plane behind the spiral is that works

>  best at about 1/4 wavelength. When the spiral is working over a 10 to
>  1
>  frequency range, that 1/4 wavelength is only on 1 frequency.
>  The antenna will have massive ripples in gain and impedance
>  when you sweep frequency.

>  I have used a commercial log spiral as a dish feed years ago.
>  It worked, it wouldn't say it worked well. Today I use either an
>  LP or a Vivaldi when I need a broad band feed.

>  Kent

>  On Thursday, May 21, 2020, 2:54:39 AM CDT, John E. Beech
>  <john@...> wrote:

>  Hi Kent,
>  I don't understand why the phase centre changes with the spiral
>  antenna as a dish feed. Do you have any mathematical reasoning/formula
>  to back this up?
>  Also I wasn't considering using a spiral mounted in a cavity for the
>  feed. My idea is to use a circular plane reflector ( splash plate),
>  positioned to adjust the feed point impedance to around 100 ohms. As
>  it stands the spiral antenna is bidirectional, like any other dipole,
>  but the phase of the radiation is different by 180 deg or put another
>  way , the front face of the spiral emits RHC while the rear face emits
>  LHC. Refelection from the dish reverses the phase so only RHC is
>  radiated in the forward direction from the dish. If a splash plate is
>  now introduced, this reflector reverses the phase and sends it back
>  towards the spiral and the dish such that it is now LHC ie in phase.
>  Again all the forward radiation is RHC. There is a slight loss of gain
>  due to the reflector/spiral assembly masking part of the dish, but
>  this is minimal provided the dish diameter is large compared to the
>  feed point diameter ( which it normally is ).
>  This type of feed should have a gain of 2-3 dB over a bare spiral,
>  which will reduce the illumination angle from 90 to 70 deg down to
>  something like 70 - 50 deg. Obviously you would need to choose the
>  dish f/D ratio to suit this angle for best performance.

>  de John G8SEQ

>  > -------Original Message-------
>  > From: KENT BRITAIN <WA5VJB@...>
>  > To: UKMicrowaves@groups.io <ukmicrowaves@groups.io>,
ukmicrowaves@groups.io <ukmicrowaves@groups.io>
>  > Subject: Re: [UKMicrowaves] Multiband dish feed
>  > Sent: May 21 '20 01:47
>  >
>  > Hi John
>  >
>  > With an LP feed you adjust the feed for best performance on the
>  > highest
>  > frequency of interest.
>  >
>  > On Lower frequencies the phase center does move a bit, but since
>  the
>  > waves are longer, phase error is quite minor.
>  >
>  > I'm afraid your Log Spiral disk does indeed effectively change
>  phase
>  > center as
>  > you go down in frequency. In contrast to the Log Periodic, the
>  spiral
>  > appears to move closer to the dish as your wavelength increases.
>  > I have produced hundreds for various clients, but due to the
>  absorber
>  > in the cavity, typical gain is in the -6 to -8 dBi range.
>  >
>  > These use 'Infinity Baluns" to take 50 Ohms to 200 Ohms balanced.
>  > They run from the back of the cavity to the center of the spirals.
>  >
>  > These are used as my Left/Right CP references on the antenna range.
>  > One of these (They made their own cavity!) is currently in orbit.
>  >
>  > Kent WA5VJB/G8EMY (Yea, an 8, but a full license)
>  >
>  > On Wednesday, May 20, 2020, 4:30:21 PM CDT, John E. Beech
>  > <john@...> wrote:
>  >
>  > Isn't variable illumination a feature of all multiband feeds? If
>  you
>  > use a log periodic the phase centre shifts, so the illumination
>  > alters. If you use a horn, the gain of the horn increases with
>  > frequency. The brief look I've had at dual band feeds have more
>  gain &
>  > therefore different illumination at the higher frequency.
>  > I do have a log periodic antenna designed to work at UHF/SHF in
>  which
>  > the phase centre does NOT change with frequency. It consists of two
>  > intertwined spirals, fed at the centre. But there is a snag or two.
>  I
>  > used to use them professionally at 888 MHz. It was a design I
>  > inherited from a previous designer (unknown). They give a
>  circularly
>  > polarised signal & their feed impedance is 188.4 ohms. This means
>  > throwing away 3 dB of gain unless you can persuade the receiving
>  > station to operate circularly polarization & practically you need
>  to
>  > be able to switch from RHC to LHC 'cos if you get it wrong then
>  > received signal is practically zilch! Normally used in a cavity
>  their
>  > impedance drops to 100 - 150 ohms. Not sure what happens if you fit
>  > them at the focal plane of a dish, but I can give it a go - it will
>  > give me something to measure with my new toy - a NanoVNA. My
>  > particular antennas are about 6 in (25 cm) diameter printed on FR4
>  Cu,
>  > tinned. They SHOULD work from about 500 MHz to 30 GHz, but I'm not
>  > sure what the tin-lead coating does at the higher frequencies. The
>  > half power beam width appears to stay constant irrespective of
>  > frequency at between 70 & 90 deg.
>  > It might be possible to control the impedance to some extent by
>  using
>  > a splash plate reflector in a dish application. If I can get it
>  down
>  > to 100 ohms then matching is relatively straightforward using a
>  > quarter wave transformer.
>  >
>  > See here:
>  > http://www.antenna-theory.com/antennas/travelling/spiral.php
>  >
>  > de John G8SEQ
>  >
>  > > -------Original Message-------
>  > > From: Andy G4JNT <andy.g4jnt@...>
>  > > To: UK Microwaves groups.io <UKMicrowaves@groups.io>
>  > > Subject: Re: [UKMicrowaves] Multiband dish feed
>  > > Sent: May 20 '20 20:58
>  > >
>  > > Just a thought.
>  > > Does a wideband antenna like a Vivaldi illuminating a dish lead
>  to
>  > a
>  > > roughly constant gain? As freq increases, beamwidth of the feed
>  > goes
>  > > down, illuminating less of the dish leading to reduced gain.
>  > >
>  > > Intuition says constant gain could be the result.
>  > >
>  > > Andy
>  > > www.g4jnt.com
>  > >
>  > > On Wed, 20 May 2020 at 20:54, KENT BRITAIN <WA5VJB@...>
>  > wrote:
>  > >
>  > > > The 1.5-15 GHz Vivaldi will take that easily.
>  > > >
>  > > > On Wednesday, May 20, 2020, 2:46:57 PM CDT, Noel G8GTZ
>  > > > <noel@...> wrote:
>  > > >
>  > > > Oh not QRO! Typically 25 watts on 2.3 and 10 watts on 3.4, 5.6
>  > and
>  > > > 10GHz - all DATV so long duty cycle compared to SSB.
>  > > >
>  > > > Noel
>  > >
>  > >
>  >
>  >






Re: Multiband dish feed

John E. Beech
 

Hi Kent,
Thanks for the explanation. I can see what is happening now. I'll try mine as it might be a neater solution than what I have previously used. I'm not interested in multiband but I am interested in producing circular polarization.
One point, won't the ripples be harmonically related? If so it might not be such a had option for amateur bands.

de John G8SEQ

-------Original Message-------
From: KENT BRITAIN <WA5VJB@FLASH.NET>
To: UKMicrowaves@groups.io <ukmicrowaves@groups.io>, ukmicrowaves@groups.io <ukmicrowaves@groups.io>
Subject: Re: [UKMicrowaves] Multiband dish feed
Sent: May 21 '20 14:57

If you mount the spiral such the focus of the dish it on the center of
the
spiral. You are well focused for high frequency range of the spiral.

But at lower frequencies the radiation tends to be from the outer
edges
of the spiral. Outside the focus area of the dish. With a BIG dish
this is less of a problem, or if the spiral is only used over a narrow
range

The problem with a simple ground plane behind the spiral is that works

best at about 1/4 wavelength. When the spiral is working over a 10 to
1
frequency range, that 1/4 wavelength is only on 1 frequency.
The antenna will have massive ripples in gain and impedance
when you sweep frequency.

I have used a commercial log spiral as a dish feed years ago.
It worked, it wouldn't say it worked well. Today I use either an
LP or a Vivaldi when I need a broad band feed.

Kent

On Thursday, May 21, 2020, 2:54:39 AM CDT, John E. Beech
<john@g8seq.com> wrote:

Hi Kent,
I don't understand why the phase centre changes with the spiral
antenna as a dish feed. Do you have any mathematical reasoning/formula
to back this up?
Also I wasn't considering using a spiral mounted in a cavity for the
feed. My idea is to use a circular plane reflector ( splash plate),
positioned to adjust the feed point impedance to around 100 ohms. As
it stands the spiral antenna is bidirectional, like any other dipole,
but the phase of the radiation is different by 180 deg or put another
way , the front face of the spiral emits RHC while the rear face emits
LHC. Refelection from the dish reverses the phase so only RHC is
radiated in the forward direction from the dish. If a splash plate is
now introduced, this reflector reverses the phase and sends it back
towards the spiral and the dish such that it is now LHC ie in phase.
Again all the forward radiation is RHC. There is a slight loss of gain
due to the reflector/spiral assembly masking part of the dish, but
this is minimal provided the dish diameter is large compared to the
feed point diameter ( which it normally is ).
This type of feed should have a gain of 2-3 dB over a bare spiral,
which will reduce the illumination angle from 90 to 70 deg down to
something like 70 - 50 deg. Obviously you would need to choose the
dish f/D ratio to suit this angle for best performance.

de John G8SEQ

> -------Original Message-------
> From: KENT BRITAIN <WA5VJB@FLASH.NET>
> To: UKMicrowaves@groups.io <ukmicrowaves@groups.io>,
ukmicrowaves@groups.io <ukmicrowaves@groups.io>
> Subject: Re: [UKMicrowaves] Multiband dish feed
> Sent: May 21 '20 01:47
>
> Hi John
>
> With an LP feed you adjust the feed for best performance on the
> highest
> frequency of interest.
>
> On Lower frequencies the phase center does move a bit, but since
the
> waves are longer, phase error is quite minor.
>
> I'm afraid your Log Spiral disk does indeed effectively change
phase
> center as
> you go down in frequency. In contrast to the Log Periodic, the
spiral
> appears to move closer to the dish as your wavelength increases.
> I have produced hundreds for various clients, but due to the
absorber
> in the cavity, typical gain is in the -6 to -8 dBi range.
>
> These use 'Infinity Baluns" to take 50 Ohms to 200 Ohms balanced.
> They run from the back of the cavity to the center of the spirals.
>
> These are used as my Left/Right CP references on the antenna range.
> One of these (They made their own cavity!) is currently in orbit.
>
> Kent WA5VJB/G8EMY (Yea, an 8, but a full license)
>
> On Wednesday, May 20, 2020, 4:30:21 PM CDT, John E. Beech
> <john@g8seq.com> wrote:
>
> Isn't variable illumination a feature of all multiband feeds? If
you
> use a log periodic the phase centre shifts, so the illumination
> alters. If you use a horn, the gain of the horn increases with
> frequency. The brief look I've had at dual band feeds have more
gain &
> therefore different illumination at the higher frequency.
> I do have a log periodic antenna designed to work at UHF/SHF in
which
> the phase centre does NOT change with frequency. It consists of two
> intertwined spirals, fed at the centre. But there is a snag or two.
I
> used to use them professionally at 888 MHz. It was a design I
> inherited from a previous designer (unknown). They give a
circularly
> polarised signal & their feed impedance is 188.4 ohms. This means
> throwing away 3 dB of gain unless you can persuade the receiving
> station to operate circularly polarization & practically you need
to
> be able to switch from RHC to LHC 'cos if you get it wrong then
> received signal is practically zilch! Normally used in a cavity
their
> impedance drops to 100 - 150 ohms. Not sure what happens if you fit
> them at the focal plane of a dish, but I can give it a go - it will
> give me something to measure with my new toy - a NanoVNA. My
> particular antennas are about 6 in (25 cm) diameter printed on FR4
Cu,
> tinned. They SHOULD work from about 500 MHz to 30 GHz, but I'm not
> sure what the tin-lead coating does at the higher frequencies. The
> half power beam width appears to stay constant irrespective of
> frequency at between 70 & 90 deg.
> It might be possible to control the impedance to some extent by
using
> a splash plate reflector in a dish application. If I can get it
down
> to 100 ohms then matching is relatively straightforward using a
> quarter wave transformer.
>
> See here:
> http://www.antenna-theory.com/antennas/travelling/spiral.php
>
> de John G8SEQ
>
> > -------Original Message-------
> > From: Andy G4JNT <andy.g4jnt@gmail.com>
> > To: UK Microwaves groups.io <UKMicrowaves@groups.io>
> > Subject: Re: [UKMicrowaves] Multiband dish feed
> > Sent: May 20 '20 20:58
> >
> > Just a thought.
> > Does a wideband antenna like a Vivaldi illuminating a dish lead
to
> a
> > roughly constant gain? As freq increases, beamwidth of the feed
> goes
> > down, illuminating less of the dish leading to reduced gain.
> >
> > Intuition says constant gain could be the result.
> >
> > Andy
> > www.g4jnt.com
> >
> > On Wed, 20 May 2020 at 20:54, KENT BRITAIN <WA5VJB@flash.net>
> wrote:
> >
> > > The 1.5-15 GHz Vivaldi will take that easily.
> > >
> > > On Wednesday, May 20, 2020, 2:46:57 PM CDT, Noel G8GTZ
> > > <noel@noelandsally.net> wrote:
> > >
> > > Oh not QRO! Typically 25 watts on 2.3 and 10 watts on 3.4, 5.6
> and
> > > 10GHz - all DATV so long duty cycle compared to SSB.
> > >
> > > Noel
> >
> >
>
>


Re: Silver plated N plugs?

ian hope (2E0IJH)
 

Give Henry a Call, http://www.whwestlake.co.uk/
 
Ian
2E0IJH

 
 
Sent: Thursday, May 21, 2020 at 3:30 PM
From: "Stephen Tompsett" <stephen@...>
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] Silver plated N plugs?

Try Barenco e.g. https://www.barenco.co.uk/rf-connectors/n-connectors/n-plug-male I have found them to be a useful supplier of connectors for 'odd sized coax.

On 21/05/2020 12:30, Robin Szemeti wrote:
Years ago, you used to be able to get good quality silver plated N type plugs military surplus, for roughly RG213 size cable.  They typically came in a little heat sealed plastic packet with a military part number on a slip of paper, at one time they were very common at rallies.
 
I don't suppose anyone can recall which of the traders sells them?  I'd dearly like to get some more!  They were excellent as the basis for oddball connectors with custom internals as they have a long body and are silver plated brass, not that chrome plated crap everyone else seems to sell, and I need to make some up for .250 sized PTFE coax ...
 
image.png
 

--
Best regards,

Robin Szemeti

Redpoint Consulting Limited

E: robin@...
T: +44 (0) 1299 405028
M: +44 (0) 7971 883371

CONFIDENTIALITY NOTICE
The information contained in this e-mail is intended only for the
confidential use of the above named recipient. If you are not the
intended recipient or person responsible for delivering it to the
intended recipient, you have received this communication in error
and must not distribute or copy it.
Please accept the sender's apologies, notify the sender immediately
by return e-mail and delete this communication.

Thank you. 
--
Stephen Tompsett (G8LYB)
Tel: 01788 578940
Mob: 07956 855816


Re: Multiband dish feed

DD1US
 

Hi Kent,

Yes, it is a special designed quad logper design. It is difficult to manufacture, especially the broadband balun/matching.

I would like to use it for the frequency range 1.2 GHZ to 10.7 GHz.

Kind regards

Matthias

www.dd1us.de

Von: KENT BRITAIN
Gesendet: Donnerstag, 21. Mai 2020 16:00
An: UKMicrowaves@groups.io; UKMicrowaves@groups.io
Antwort an: UKMicrowaves@groups.io
Betreff: Re: [UKMicrowaves] Multiband dish feed

The highly compressed quad log periodics?

That has to be a  @$%@%! to build! hihi

What frequency range are you looking at?

Kent

On Thursday, May 21, 2020, 8:28:18 AM CDT, DD1US <matthias.bopp@...> wrote:


Hi Kent,

 

Thank you very much.

 

I just wanted to make sure that my thought process is right and I am not wasting time in trying to build a system around such a feed.

 

The concept with the stepped ground plane is interesting however your experiment with the thermal sensitive plastic suggests, that
it might now be very successful
😉

 

I am kind of searching of the holy grail of a broadband feed for a dish … not for professional use just for my hobby and presently the

“eleven feed” seems to come quite close … have you looked into that ?

 

Kind regards

 

Matthias

 

www.dd1us.de

 

 

Von: UKMicrowaves@groups.io <UKMicrowaves@groups.io> Im Auftrag von KENT BRITAIN
Gesendet: Donnerstag, 21. Mai 2020 15:14
An: UKMicrowaves@groups.io; UKMicrowaves@groups.io
Betreff: Re: [UKMicrowaves] Multiband dish feed

 

Hi Matt

 

You are quite correct, your LNA will never see cold sky with a log spiral feed.

Virtually all the Log Spirals are used in Electronic Warfare, most commonly

on aircraft to detect radar signals.   Those are very high power pulses

so the low gain and high noise temperature are not an issue.

 

There are techniques where a stepped ground plane is put behind the

spiral instead of absorber.  But you have to know a lot about the radiation

off your spiral to properly design that stepped ground plane.

 

Yeas ago I watched an interesting demonstration with a log spiral.

They used a thin sheet of thermal sensitive plastic.  The stuff that just

the heat of your hand would make it change colour.  We put that plastic

over the spiral and feed just over a watt of RF into it.  You saw colour

changes at the active area of the antenna.  Then we slowly swept frequency. 

The active areas jumped all over the place.     It was NOT a

smooth transition from the center to the

outer parts of the spiral.   The RF always from a spot to resonate, but

there was no logic to the pattern changes.

 

On the BIG dishes  ( 30+ meters) they like to use a Ridged Horn when they need a

broad band feed.   I like to think of a Vivaldi antenna as a ridged horn

without the horn.    The vivaldi is also used as a dish feed on several military

ELINT systems.     I hope this helps    Kent

 

On Thursday, May 21, 2020, 1:41:16 AM CDT, DD1US <matthias.bopp@...> wrote:

 

 

Hi Kent and John,

 

Thank you very much for this interesting discussion.

 

I have a question related to such a cavity backed spiral log periodic antenna:

 

I would like to use such an antenna as a feed in a parabolic dish, especially for satellite communication.

 

For TX half the power is lost in the absorber material of the cavity, which might be acceptable in my applications.
However, I have to see what the maximum power will be, which I can use, as the absorber material will get apparently hot
at higher power.

 

For RX my understanding is, that the absorber material is warm, let assume at ambient temperature, and thus radiates
a lot of thermal noise which is received by the spiral antenna. This noise will completely ruin the G/T and I will not be
able to receive weak satellite signals which is possible with other antennas as the background noise in the cold sky is low.

 

Maybe the same cavity backed spiral feed mounted in a dish “on the satellite” which is pointed to Earth might work,
as the feed is quite cold (when not exposed to the sun) and the background noise received by the dish is the warm Earth anyway.

 

Is my understanding correct which means there is no point in using such a cavity backed spiral log periodic feed for a satellite

groundstation ?

 

Many thanks in advance for your feedback.

 

Kind regards

 

Matthias

 

www.dd1us.de

 

 

 

 

Von: UKMicrowaves@groups.io <UKMicrowaves@groups.io> Im Auftrag von KENT BRITAIN
Gesendet: Donnerstag, 21. Mai 2020 02:47
An: UKMicrowaves@groups.io; ukmicrowaves@groups.io
Betreff: Re: [UKMicrowaves] Multiband dish feed

 

Hi John

 

With an LP feed you adjust the feed for best performance on the highest

frequency of interest.

 

On Lower frequencies the phase center does move a bit, but since the

waves are longer, phase error is quite minor.

 

I'm afraid your Log Spiral disk does indeed effectively change phase center as

you go down in frequency.   In contrast to the Log Periodic, the spiral

appears to move closer to the dish as your wavelength increases.

I have produced hundreds for various clients, but due to the absorber

in the cavity, typical gain is in the -6 to -8 dBi range.

 

These use 'Infinity Baluns" to take 50 Ohms to 200 Ohms balanced.

They run from the back of the cavity to the center of the spirals.

 

These are used as my Left/Right CP references on the antenna range.

One of these (They made their own cavity!) is currently in orbit.

 

Kent WA5VJB/G8EMY  (Yea, an 8, but a full license)

 

 

 

On Wednesday, May 20, 2020, 4:30:21 PM CDT, John E. Beech <john@...> wrote:

 

 

Isn't variable illumination a feature of all multiband feeds? If you use a log periodic the phase centre shifts, so the illumination alters. If you use a horn, the gain of the horn increases with frequency. The brief look I've had at dual band feeds have more gain & therefore different illumination at the higher frequency.
          I do have a log periodic antenna designed to work at UHF/SHF in which the phase centre does NOT change with frequency. It consists of two intertwined spirals, fed at the centre. But there is a snag or two. I used to use them professionally at 888 MHz. It was a design I inherited from a previous designer (unknown). They give a circularly polarised signal & their feed impedance is 188.4 ohms. This means throwing away 3 dB of gain unless you can persuade the receiving station to operate circularly polarization & practically you need to be able to switch from RHC to LHC 'cos if you get it wrong then received signal is practically zilch! Normally used in a cavity their impedance drops to 100 - 150 ohms. Not sure what happens if you fit them at the focal plane of a dish, but I can give it a go - it will give me something to measure with my new toy - a NanoVNA. My particular antennas are about  6 in (25 cm) diameter printed on FR4 Cu, tinned. They SHOULD work from about 500 MHz to 30 GHz, but I'm not sure what the tin-lead coating does at the higher frequencies. The half power beam width appears to stay constant irrespective of frequency at between 70 & 90 deg.
          It might be possible to control the impedance to some extent by using a splash plate reflector in a dish application. If I can get it down to 100 ohms then matching is relatively straightforward using a quarter wave transformer.

See here:  http://www.antenna-theory.com/antennas/travelling/spiral.php

de John G8SEQ

>  -------Original Message-------
>  From: Andy G4JNT <andy.g4jnt@...>
>  To: UK Microwaves groups.io <UKMicrowaves@groups.io>
>  Subject: Re: [UKMicrowaves] Multiband dish feed
>  Sent: May 20 '20 20:58

>  Just a thought.
>  Does a wideband antenna like a Vivaldi illuminating a dish lead to a
>  roughly constant gain? As freq increases, beamwidth of the feed goes
>  down, illuminating less of the dish leading to reduced gain.

>  Intuition says constant gain could be the result.

>  Andy
www.g4jnt.com

>  On Wed, 20 May 2020 at 20:54, KENT BRITAIN <WA5VJB@...> wrote:

>  > The 1.5-15 GHz Vivaldi will take that easily.
>  >
>  > On Wednesday, May 20, 2020, 2:46:57 PM CDT, Noel G8GTZ
>  > <noel@...> wrote:
>  >
>  > Oh not QRO! Typically 25 watts on 2.3 and 10 watts on 3.4, 5.6 and
>  > 10GHz - all DATV so long duty cycle compared to SSB.
>  >
>  > Noel




Re: Silver plated N plugs?

Stephen Tompsett
 

Try Barenco e.g. https://www.barenco.co.uk/rf-connectors/n-connectors/n-plug-male I have found them to be a useful supplier of connectors for 'odd sized coax.

On 21/05/2020 12:30, Robin Szemeti wrote:
Years ago, you used to be able to get good quality silver plated N type plugs military surplus, for roughly RG213 size cable.  They typically came in a little heat sealed plastic packet with a military part number on a slip of paper, at one time they were very common at rallies.

I don't suppose anyone can recall which of the traders sells them?  I'd dearly like to get some more!  They were excellent as the basis for oddball connectors with custom internals as they have a long body and are silver plated brass, not that chrome plated crap everyone else seems to sell, and I need to make some up for .250 sized PTFE coax ...

image.png


--
Best regards,

Robin Szemeti

Redpoint Consulting Limited 

E: robin@... 
T: +44 (0) 1299 405028 
M: +44 (0) 7971 883371 

CONFIDENTIALITY NOTICE 
The information contained in this e-mail is intended only for the
confidential use of the above named recipient. If you are not the
intended recipient or person responsible for delivering it to the
intended recipient, you have received this communication in error 
and must not distribute or copy it. 
Please accept the sender's apologies, notify the sender immediately 
by return e-mail and delete this communication. 

Thank you. 
-- 
Stephen Tompsett (G8LYB)
Tel: 01788 578940
Mob: 07956 855816

8481 - 8500 of 64110