Date   

Calculating the impedance of a dielectric rod in free space to get a match to 377 ohms?

Neil Smith G4DBN
 

I'm doing some simulations of dielrod/dielspike horns using a simple taper from a round waveguide down to a round rod.  The plan is to set the diameter of the round rod extension such that it has the same impedance as free space, so there is no discontinuity at the end of the taper, and hopefully to minimise reflections.

Can anyone point me at a way to calculate the diameter of a dielectric rod guide to get the impedance of the terminal extension close to 377 ohms?  At the moment, I'm just fiddling with the diameter to see if I can reduce the sidelobes a little, but I'd prefer to set the rod to a known size, then adjust the length of the rod and the taper angle.

The dielectric plastic is Rexolite 1422, with a dielectric "constant"  of 2.53. 

Neil G4DBN


Re: Feedthrough capacitor wanted

G4WIM KT6UK
 

Andy,

I had the same problem when building my 13cm PA - I had the feed thru's but they were an American thread, landed up buying a tap from China to match the thread pitch / size.

Worked out a lot cheaper than buying new metric feed thru's.

73 Tim


Re: New 241 GHz record (via F1VL)

militaryoperator
 


I can usually work into netherlands/france/Jersey with 50W on 70cm from my location, and I have to beam through the hill that you sit on ... I was otherwise occupied on Tuesday, will be on 6m on Thursday though.



Fantastic. 

Best last night here in 432FMAC was just 62Km, with 50W to X5000 colinear at 50ft. 

Mind you, someone got 112Km with 25W and a dipole......... apparently!.
I wonder how high the dipole was?

Seems I'm wasting my time and efforts in some respects. 

Ben G4BXD

--
Robin Szemeti - G1YFG
_._,_._,_


Re: New 241 GHz record (via F1VL)

Neil Smith G4DBN
 

On 10/03/2021 11:22, militaryoperator via groups.io wrote:

Seems I'm wasting my time and efforts in some respects.
Hi Ben, time spent playing on the radio is never wasted though. It is far better than time spent NOT playing on the radio...

I often struggled to make 50 km in the 432 FMAC using an 18-ele beam and my handheld, even with it vertical, so you are doing better than I was.

There is a lot of chat around how the 20 mW at 241 GHz was generated. With 57 dBi gain, that is a mighty EIRP, and then the little matter of climbing a mountain and having an optical path does tend to add a shedload of dBs to the signal!

Nel G4DBN


Re: New 241 GHz record (via F1VL)

Robin Szemeti - G1YFG
 

I can usually work into netherlands/france/Jersey with 50W on 70cm from my location, and I have to beam through the hill that you sit on ... I was otherwise occupied on Tuesday, will be on 6m on Thursday though.

On Wed, 10 Mar 2021 at 11:22, militaryoperator via groups.io <Military1944=aol.com@groups.io> wrote:
New IARU R1 record on 241 GHz. QSO 6 March 2020, 17.10 UTC between:
DK5NJ at JO50TI29JN 690m ASL Schwedenwache (DK0NA) and DB6NT at JO60GJ03MN 896m ASL Aschberg (Saxe).
Distance 63.987 km.
--------------------------------

Fantastic. 

Best last night here in 432FMAC was just 62Km, with 50W to X5000 colinear at 50ft. 

Mind you, someone got 112Km with 25W and a dipole......... apparently!.
I wonder how high the dipole was?

Seems I'm wasting my time and efforts in some respects. 

Ben G4BXD


--
Robin Szemeti - G1YFG


Re: New 241 GHz record (via F1VL)

militaryoperator
 

New IARU R1 record on 241 GHz. QSO 6 March 2020, 17.10 UTC between:
DK5NJ at JO50TI29JN 690m ASL Schwedenwache (DK0NA) and DB6NT at JO60GJ03MN 896m ASL Aschberg (Saxe).
Distance 63.987 km.
--------------------------------

Fantastic. 

Best last night here in 432FMAC was just 62Km, with 50W to X5000 colinear at 50ft. 

Mind you, someone got 112Km with 25W and a dipole......... apparently!.
I wonder how high the dipole was?

Seems I'm wasting my time and efforts in some respects. 

Ben G4BXD


New 241 GHz record (via F1VL)

Neil Smith G4DBN
 

Tks F1VL on hyperfr-ref for this news snippet from DB6NT and DK5NJ. Marvellous stuff

Neil G4DBN

https://www.youtube.com/watch?v=eVJC4lfpyuo

New IARU R1 record on 241 GHz. QSO 6 March 2020, 17.10 UTC between:

DK5NJ at JO50TI29JN 690m ASL Schwedenwache (DK0NA) and DB6NT at JO60GJ03MN 896m ASL Aschberg (Saxe).
Distance 63.987 km.
Reports 559/599.
Temp -1C, RH 45%.
Both receivers used a sub-harmonic mixer drive by a 120 GHz LO
Transmit power 20 mW
Both ends used 40 cm dishes with a gain of 57 dB and a beasmwidth of less than 0.25°
This was a line of sight path, and alignment was done using riflescopes
Signal strength was around 30dB over noise, suggesting the possibility that 100 km could have been achieved under those conditions.


Re: Feedthrough capacitor wanted

Andy G4JNT
 

I have dozens, nay hundreds possibly,  of second-hand feedthroughs of all sizes.   They are one of the items worth recovering above all else from scrap rally-purchases, being so expensive bought new.
However, having said that, there aren't many in there with a thread diameter of 4mm.  Some measure at 4.5mm and many 5.5 or 6mm

I was going to say  PM me your address, but Roger's message just-now popped up to say he had loads of that size, so better off there.    
But if anyone else needs larger feed throughs, I do have a wide selection...   See photo attached ...

Actually it's damned annoying.   Most of them have coarse American threads and I have no or very few nuts suitable, so quite often end up soldering in threaded types - which sometimes damages them and always looks untidy.    The only metric threaded feedthroughs have generally come from Eu built ex mob phone etc kit - which is usually too good in itself to just rip apart from the components.


FeedThros.jpg


On Wed, 10 Mar 2021 at 07:59, John Lemay <john@...> wrote:
I'm looking for just one feedthrough capacitor, to replace a failed item:

The most important feature is the screw-in thread, which needs to be 8-32,
to fit the tapped hole in my case. Overall length about 20mm. Capacitance
value is unimportant and the working voltage only needs to be 24v.

Anyone got one tucked away in the spare component drawer ?

Tip: 8-32 thread looks like M4 at first glance.

Thanks

John G4ZTR



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Re: Feedthrough capacitor wanted

John Lemay
 

Roger

That would be brilliant thanks !

I'll drop you my address on a PM.

John

-----Original Message-----
From: UKMicrowaves@groups.io [mailto:UKMicrowaves@groups.io] On Behalf Of Roger Ray via groups.io
Sent: 10 March 2021 08:17
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] Feedthrough capacitor wanted

Hi John,

I have got a few hundred 1000pF. I believe are 8/32. ie same size but will not fit a 4mm nut. I can send you a few.

Roger
On 10 Mar 2021, at 07:59, John Lemay <john@carltonhouse.eclipse.co.uk> wrote:

I'm looking for just one feedthrough capacitor, to replace a failed item:

The most important feature is the screw-in thread, which needs to be 8-32,
to fit the tapped hole in my case. Overall length about 20mm. Capacitance
value is unimportant and the working voltage only needs to be 24v.

Anyone got one tucked away in the spare component drawer ?

Tip: 8-32 thread looks like M4 at first glance.

Thanks

John G4ZTR



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https://www.avg.com






Re: Feedthrough capacitor wanted

Roger Ray
 

Hi John,

I have got a few hundred 1000pF. I believe are 8/32. ie same size but will not fit a 4mm nut. I can send you a few.

Roger

On 10 Mar 2021, at 07:59, John Lemay <john@carltonhouse.eclipse.co.uk> wrote:

I'm looking for just one feedthrough capacitor, to replace a failed item:

The most important feature is the screw-in thread, which needs to be 8-32,
to fit the tapped hole in my case. Overall length about 20mm. Capacitance
value is unimportant and the working voltage only needs to be 24v.

Anyone got one tucked away in the spare component drawer ?

Tip: 8-32 thread looks like M4 at first glance.

Thanks

John G4ZTR



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Re: DB6NT sequencer

John Lemay
 

Hi Pete

 

Very long time no speak ! Hope you’re well.

 

Yes, checked the diode and it was OK, but replaced it anyway, being cheap and easy to do.

 

Regards

 

John G4ZTR

 

From: UKMicrowaves@groups.io [mailto:UKMicrowaves@groups.io] On Behalf Of Peter Burgess via groups.io
Sent: 09 March 2021 21:45
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] DB6NT sequencer

 

Hi John

Check that the protection diode across the relay has not gone open circuit.

Peter
G4BCH


Virus-free. www.avg.com


Feedthrough capacitor wanted

John Lemay
 

I'm looking for just one feedthrough capacitor, to replace a failed item:

The most important feature is the screw-in thread, which needs to be 8-32,
to fit the tapped hole in my case. Overall length about 20mm. Capacitance
value is unimportant and the working voltage only needs to be 24v.

Anyone got one tucked away in the spare component drawer ?

Tip: 8-32 thread looks like M4 at first glance.

Thanks

John G4ZTR



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Re: 10GHz Feedhorn 60cm offset dish, looking for

Tim, VK2XAX
 

And... if you want 24GHz as well, you might ask W1GHZ about the availability of his horns.

http://w1ghz.org/

http://w1ghz.org/new/LPF10.pdf

regards

Tim


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


Re: DB6NT sequencer

Alan Melia
 


.......or more likely short circuit. Very high very short spikes can cause the PIV to reduce, then eventually the first ''relay off'' condition melts the diode. Fast good diodes are not the best snubbers, you require a dode with a fair bit of themal inertia. Particularly when techs used to ''routine'' Strowger :-))
 
Alan
G3NYK
 

----- Original Message -----
Sent: Tuesday, March 09, 2021 9:45 PM
Subject: Re: [UKMicrowaves] DB6NT sequencer

Hi John

Check that the protection diode across the relay has not gone open circuit.

Peter
G4BCH


Re: DB6NT sequencer

Peter Burgess
 

Hi John

Check that the protection diode across the relay has not gone open circuit.

Peter
G4BCH


Re: DB6NT sequencer

John Lemay
 

Geoff

 

Thanks for the suggestion, and yes, I think the series of sequencers work on similar principles, with devices of small or large capability.

 

You asked if I am sure the devices have failed – actually I’m not sure – and that idea set me on the path of simple multimeter checks. I find that the unused device and the two supposedly failed devices give similar resistance measurements. But ……… the one in use at present does not.

 

I have the sequencer in a machined aluminium case, with feedthrough capacitors for all connections. Now I’ve disconnected everything from the feedthroughs, and one of them measures about 1k ohm to chassis. It’s the one on relay –ve. How weird is that ?

 

I’m calling it a day now, but at last I feel I may have located the problem. I really don’t have much hair left ………..

 

Regards

 

John

 

 

From: UKMicrowaves@groups.io [mailto:UKMicrowaves@groups.io] On Behalf Of geoffrey pike via groups.io
Sent: 09 March 2021 21:10
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] DB6NT sequencer

 

Hi John,

I have only SEQ2 details but they may be similar. So the gate is controlled via 3v zener. Have you monitored the gate

voltage when you let the ptt go?

Are you sure the other two IRF520s have actually failed.

Good news is that IRF520s are cheap until you find the fault.

Geoff

GI0GDP

 

On Tuesday, 9 March 2021, 20:32:06 GMT, John Lemay <john@...> wrote:

 

 

Hello all

 

I'm not having much luck lately .......

 

My 13cms masthead system uses a DB6NT sequencer SEQ 4 to switch a 28v

changeover relay. At the weekend I had no receive on 13cms, transmit was

fine.

 

Delving into the box today it seems that the switching FET, an IRF520 has

gone "leaky" between drain and source. It pulls the relay into transmit

nicely, with almost 0v on the drain, but on receive there is enough voltage

remaining to hold the relay energised.

 

I've replaced the FET, twice, today and failure of the device is instant but

without drama.

 

Disconnecting the relay from the sequencer and running the relay to an

external power supply, it switches just as it should.

 

Any suggestions as to the likely cause of my sequencer problem? I have just

one FET remaining ........

 

Thanks

 

John G4ZTR

 

 

 

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Re: DB6NT sequencer

geoffrey pike
 

Hi John,
I have only SEQ2 details but they may be similar. So the gate is controlled via 3v zener. Have you monitored the gate
voltage when you let the ptt go?
Are you sure the other two IRF520s have actually failed.
Good news is that IRF520s are cheap until you find the fault.
Geoff
GI0GDP

On Tuesday, 9 March 2021, 20:32:06 GMT, John Lemay <john@...> wrote:


Hello all

I'm not having much luck lately .......

My 13cms masthead system uses a DB6NT sequencer SEQ 4 to switch a 28v
changeover relay. At the weekend I had no receive on 13cms, transmit was
fine.

Delving into the box today it seems that the switching FET, an IRF520 has
gone "leaky" between drain and source. It pulls the relay into transmit
nicely, with almost 0v on the drain, but on receive there is enough voltage
remaining to hold the relay energised.

I've replaced the FET, twice, today and failure of the device is instant but
without drama.

Disconnecting the relay from the sequencer and running the relay to an
external power supply, it switches just as it should.

Any suggestions as to the likely cause of my sequencer problem? I have just
one FET remaining ........

Thanks

John G4ZTR



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Re: 10GHz Feedhorn 60cm offset dish, looking for

Neil Smith G4DBN
 

Motivations were:

1) I have a load of Rexolite 1422 that I need to use up

2) Inherently waterproof and spider-resistant.

3) Small enough to fit alongside a similar model on 5.7 GHz with 2 degrees of dish nod to swap bands

It isn't going to be any better than a well-designed W2IMU or Pickett-Potter or corrugated-choke horn in terms of sidelobe suppression, but it is reasonably easy to control sidelobes and set a decent edge taper.

I'll make half a dozen and see how they look on a rotary mount, and then see what sort of sun noise I get when compared with a known horn.

Neil

On 09/03/2021 20:53, Colin Ranson wrote:

Looks nice Neil – yo a star !  as my brummy missus would say.  I don’t think I can get away with anything bigger than a Zone 2 elliptical – my house is stating to look like the Mothership in Battlestar Galactica !

 

73’s    Colin.

 

Sent from Mail for Windows 10

 

From: Neil Smith G4DBN
Sent: 09 March 2021 19:18
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] 10GHz Feedhorn 60cm offset dish, looking for

 

I'm making some lensed dielspike horns with a collar to fit a 40mm feedhorn clamp on an offset dish, they have an aluminium body with an SMA connector and a truncated conical Rexolite 1422 lens similar to the ones designed by HB9PZK for QO-100.  The cone angle is calculated to give a 12dB edge taper on a typical 80cm offset dish

They are sealed units and designed to be left out in the rain. I haven't tried doing them with an N connector mainly on cost grounds, but it should be feasible to use an N connector with a reduced SMA base in exactly the same unit, so long as it has a 4.06 mm PTFE sleeve.  You could probably modify any SMA-equipped transition to use one of these N types (perhaps from someone cheaper than H&S!)



Re: 10GHz Feedhorn 60cm offset dish, looking for

Colin Ranson
 

Looks nice Neil – yo a star !  as my brummy missus would say.  I don’t think I can get away with anything bigger than a Zone 2 elliptical – my house is stating to look like the Mothership in Battlestar Galactica !

 

73’s    Colin.

 

Sent from Mail for Windows 10

 

From: Neil Smith G4DBN
Sent: 09 March 2021 19:18
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] 10GHz Feedhorn 60cm offset dish, looking for

 

I'm making some lensed dielspike horns with a collar to fit a 40mm feedhorn clamp on an offset dish, they have an aluminium body with an SMA connector and a truncated conical Rexolite 1422 lens similar to the ones designed by HB9PZK for QO-100.  The cone angle is calculated to give a 12dB edge taper on a typical 80cm offset dish

They are sealed units and designed to be left out in the rain. I haven't tried doing them with an N connector mainly on cost grounds, but it should be feasible to use an N connector with a reduced SMA base in exactly the same unit, so long as it has a 4.06 mm PTFE sleeve.  You could probably modify any SMA-equipped transition to use one of these N types (perhaps from someone cheaper than H&S!)

This horn is aimed at folks who are building the F6BVA transverter and don't want to use waveguide.  I haven't announced it yet as I'm still optimising the tapers and pin position. Target price is under £30.

Neil G4DBN

Something like this:

with the lenses being similar to those HB9PZKs I made last year

or perhaps just with a long rear taper like these I made:

On 09/03/2021 15:28, Mike Willis wrote:

You can make one fairly easily out of plumbing fittings, but if you are one of those who has to buy and nobody has a spare the usual suspects can provide. RFHAM, Procom. Passion Radio...

 

 


Re: DB6NT sequencer

ian hope (2E0IJH)
 

You having about as much luck as me, I've had no changeover on my 2m system, 13.4v there on or off load, but relay wouldn't switch, works fine on bench, in the end meggered the cable less than 100 ohms between cores, No damage, ends clean, cut it half and several pints of water poured out a 12 core YY cable, figure that
 
Ian
M5IJH

 
 
Sent: Tuesday, March 09, 2021 at 8:31 PM
From: "John Lemay" <john@...>
To: UKMicrowaves@groups.io
Subject: [UKMicrowaves] DB6NT sequencer
Hello all

I'm not having much luck lately .......

My 13cms masthead system uses a DB6NT sequencer SEQ 4 to switch a 28v
changeover relay. At the weekend I had no receive on 13cms, transmit was
fine.

Delving into the box today it seems that the switching FET, an IRF520 has
gone "leaky" between drain and source. It pulls the relay into transmit
nicely, with almost 0v on the drain, but on receive there is enough voltage
remaining to hold the relay energised.

I've replaced the FET, twice, today and failure of the device is instant but
without drama.

Disconnecting the relay from the sequencer and running the relay to an
external power supply, it switches just as it should.

Any suggestions as to the likely cause of my sequencer problem? I have just
one FET remaining ........

Thanks

John G4ZTR



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