Date   

Re: 1.9 to 2m Mesh Dish

John Fell
 

I think G3GRO used a 12ft segment dish - like a radar cheese but rotated through 90 degrees and only 12" wide , with stand offs from vertical mast to maintain parabolic form.Long time ago .....

John
G0API

On Mon, 29 Jul 2019 at 16:42, Ken G3YKI <kenneth@...> wrote:
John credits me with a more ambitious construction than it actually was. It was 8ft square. The 4 ft. square panels could be stacked on the top of a small car and that was the usual mode of transport, though we did use the lorry once. The feed was a dual dipole feed, which I still have.
I recall that G3GRO did something similar and described it in a meeting at some event (was that 12 ft High by 8ft?).


Re: 1.9 to 2m Mesh Dish PS.

John E. Beech
 

Hi Again Ken,
I'm giving a general talk on antennas at Stratford Club. Can I have your permission to use your photo as part of the talk?

de John G8SEQ

-------Original Message-------
From: Ken G3YKI <kenneth@hince.plus.com>
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 1.9 to 2m Mesh Dish
Sent: Jul 29 '19 16:42

John credits me with a more ambitious construction than it actually
was. It was 8ft square. The 4 ft. square panels could be stacked on
the top of a small car and that was the usual mode of transport,
though we did use the lorry once. The feed was a dual dipole feed,
which I still have.
I recall that G3GRO did something similar and described it in a
meeting at some event (was that 12 ft High by 8ft?).


Re: 1.9 to 2m Mesh Dish

John E. Beech
 

Hi Ken,
Come on - it was about thirty odd years ago! And my memory ain't that good. I do remember you totally misaligned your receiver for 13 cms & I knocked up a Schottky diode harmonic mixer driven by 100 mW handheld to provide you with a signal to get you back in the right ball park. You said it wouldn't work but it did and enabled you to find the beacon again & tune up on that.
Is the photo at Dunstable Downs? Looks very familiar.

-------Original Message-------
From: Ken G3YKI <kenneth@hince.plus.com>
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 1.9 to 2m Mesh Dish
Sent: Jul 29 '19 16:42

John credits me with a more ambitious construction than it actually
was. It was 8ft square. The 4 ft. square panels could be stacked on
the top of a small car and that was the usual mode of transport,
though we did use the lorry once. The feed was a dual dipole feed,
which I still have.
I recall that G3GRO did something similar and described it in a
meeting at some event (was that 12 ft High by 8ft?).


Re: Just a suggestion

Neil Smith G4DBN
 

And might I make a plea for a quick QRZ? even if there is another sked in the queue?  There are some stations in various microwave contests who are not on KST or anything else I can find, so having a QSO is just random chance of dish alignment or scatter, but I might just be listening to the tail end of another QSO and hearing them OK.  If it isn't their frequency, if they just announced "QSY 130" after their contact, then sent a quick CQ on that frequency, it would give me a chance of catching them.

I often try to slip in a "G9XXX 140 please", but if the station who is running on the frequency doesn't leave a millisecond gap, that usually fails.

Maybe I just need Moar Power, Igor.

Actually, I just need to get my bloody finger out and finish the move of the antennas and kit between masts, so I can get back on the air, but Life keeps intervening.

Neil G4DBN

On 29/07/2019 16:32, Ken G3YKI wrote:
Out of 10 contacts 4 were direct on 10GHz. Don't forget to call CQ when there is rain about, (and QRZ at the end of a contact!)


Re: 1.9 to 2m Mesh Dish

 

John credits me with a more ambitious construction than it actually was. It was 8ft square. The 4 ft. square panels could be stacked on the top of a small car and that was the usual mode of transport, though we did use the lorry once. The feed was a dual dipole feed, which I still have.
I recall that G3GRO did something similar and described it in a meeting at some event (was that 12 ft High by 8ft?).


Re: Just a suggestion

 

Out of 10 contacts 4 were direct on 10GHz. Don't forget to call CQ when there is rain about, (and QRZ at the end of a contact!)


Re: Just a suggestion

G3UVR Denis IO83KH
 

To Adrian.

We were all on KST.. 144.390 does not have the range needed to set up skeds for microwave unless you have a multi aerial array and +300w

I did forget to log into Zello but otherwise happy with the eight contacts I did setup via KST.

KST wins again.

73 de Denis G3UVR


Re: Just a suggestion

John Worsnop
 

P s I'd be happy to feature initials for reports to Scatterpoint /RadCom if you tell me the initial # in your report to me

73 John


Re: Just a suggestion

John Worsnop
 

I agree with Neil. Let's not make contests harder than they need to be. 
Getting out/P or in the shack should be the main objective. 
The concept of "initials" as used in EME where you keep a list of every new station you work is a good way to add some interest to the GHz bands. 
One, it encourages people to look for new stations rather than just DX and two, it encourages new stations to build for the band and people will search them out even if they are not DX or in rare squares.

What do the rest of you think about getting this idea going?

73 John



On Mon, 29 Jul 2019, 16:15 Neil Smith G4DBN, <neil@...> wrote:
A unique string of five groups of five characters/numbers for each
contact, generated in advance by the contest website, would make sure we
were actually communicating and keep us on our toes. I would suggest
QTCs, as in the WAEDX contests
https://www.darc.de/der-club/referate/referat-conteste/worked-all-europe-dx-contest/en/
but with small numbers of contacts, that isn't ideal.  Depends what the
point of the contest is though.  I love the challenge of copying QTCs
send at mega-fast speed in CW, but if we want to encourage activity,
making the contest harder might not be the best move.

Neil G4DBN


On 29/07/2019 14:27, Tony G4NBS via Groups.Io wrote:
> You mean you need to know both the call sign and locator in advance John? Whatever happened to exchanging all info on the band concerned!
> Toungue in cheek of course but wonder if it’s worth considering a reintroduction of some form of info required that guarantees a unique exchange?
> Not thinking of the old exchanges of miles from nowhere but some form of code that changes each band/contest??
> Having just listened to IOTA test with it’s optional RS(T) it was amusing to hear all the repeats of serials required when everything else was known......
> Back in my hole!
> 73
> Tony G4nbs
>> On 29 Jul 2019, at 13:07, John Lemay <john@...> wrote:
>>
>> Yesterday in the 10GHz contest I spent a while trying (and failing) to work
>> a particular station. Just as I was giving up, it came to light that that G
>> station had crossed the boundary into GW and was portable about 15 degrees
>> off the heading I was using. It only takes a minute to edit ones user
>> details on 'KST ...........
>>
>> John G4ZTR
>>
>> Aka Grumpy of Colchester
>>
>>
>>
>>
>>
>
>
>
>




Re: 1.9 to 2m Mesh Dish

John E. Beech
 

Hi Bob,
That reminds me of a large dish one of the AERIEL contest group used to use. It was a "square paraboloid" made of four square wooden sections* which bolted together to form a larger square of about 12 ft on a side. He used to transport it in knocked down form ie 6 ft squares in his girlfriends horse box, along with all the other gear. The refecting surface was 1/2 inch chicken wire. Very effective & light weight for its size. You could make something similar ( smaller) in an afternoon with a jig-saw, hammer & staples, some screws and a drill. I can't remember much about the feed; I think that was a wooden arm and a "coffee can" connected to TRx by LDF450 or similar.

* wood was 1/2 inch thick plywood sheet about six inches wide cut to required parabola along one edge.

de John G8SEQ

-------Original Message-------
From: Bob_G1ZJP <R_Offer@hotmail.co.uk>
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: [UKMicrowaves] 1.9 to 2m Mesh Dish
Sent: Jul 29 '19 14:25

Hi All

I'm musing the idea of trying a mesh dish for 23cms & 13cms and would
like to get as close to but not exceeding 2m.

Before I explore sources on the internet, does anyone reasonably close
to Lincolnshire [try me to see if you're close enough], have one to
sell please?

If no one wants to sell, then do others have any recommendations /
sources of supply, please?

Thanks
Bob, G1ZJP / M1MHZ


Re: Just a suggestion

Neil Smith G4DBN
 

A unique string of five groups of five characters/numbers for each contact, generated in advance by the contest website, would make sure we were actually communicating and keep us on our toes. I would suggest QTCs, as in the WAEDX contests https://www.darc.de/der-club/referate/referat-conteste/worked-all-europe-dx-contest/en/ but with small numbers of contacts, that isn't ideal.  Depends what the point of the contest is though.  I love the challenge of copying QTCs send at mega-fast speed in CW, but if we want to encourage activity, making the contest harder might not be the best move.

Neil G4DBN

On 29/07/2019 14:27, Tony G4NBS via Groups.Io wrote:
You mean you need to know both the call sign and locator in advance John? Whatever happened to exchanging all info on the band concerned!
Toungue in cheek of course but wonder if it’s worth considering a reintroduction of some form of info required that guarantees a unique exchange?
Not thinking of the old exchanges of miles from nowhere but some form of code that changes each band/contest??
Having just listened to IOTA test with it’s optional RS(T) it was amusing to hear all the repeats of serials required when everything else was known......
Back in my hole!
73
Tony G4nbs
On 29 Jul 2019, at 13:07, John Lemay <john@carltonhouse.eclipse.co.uk> wrote:

Yesterday in the 10GHz contest I spent a while trying (and failing) to work
a particular station. Just as I was giving up, it came to light that that G
station had crossed the boundary into GW and was portable about 15 degrees
off the heading I was using. It only takes a minute to edit ones user
details on 'KST ...........

John G4ZTR

Aka Grumpy of Colchester






Re: Just a suggestion

Adrian G4UVZ
 

At least you worked someone...I called on and off during the day on 144.390  and worked no one!


Re: Just a suggestion

John Worsnop
 

Or you could just both have swung your dishes a bit. 10GHz paths especially by scatter are rarely boresight direction. 


On Mon, 29 Jul 2019, 14:07 John Lemay, <john@...> wrote:
Yesterday in the 10GHz contest I spent a while trying (and failing) to work
a particular station. Just as I was giving up, it came to light that that G
station had crossed the boundary into GW and was portable about 15 degrees
off the heading I was using. It only takes a minute to edit ones user
details on 'KST ...........

John G4ZTR

Aka Grumpy of Colchester






Re: Just a suggestion

Tony G4NBS
 

You mean you need to know both the call sign and locator in advance John? Whatever happened to exchanging all info on the band concerned!
Toungue in cheek of course but wonder if it’s worth considering a reintroduction of some form of info required that guarantees a unique exchange?
Not thinking of the old exchanges of miles from nowhere but some form of code that changes each band/contest??
Having just listened to IOTA test with it’s optional RS(T) it was amusing to hear all the repeats of serials required when everything else was known......
Back in my hole!
73
Tony G4nbs

On 29 Jul 2019, at 13:07, John Lemay <john@carltonhouse.eclipse.co.uk> wrote:

Yesterday in the 10GHz contest I spent a while trying (and failing) to work
a particular station. Just as I was giving up, it came to light that that G
station had crossed the boundary into GW and was portable about 15 degrees
off the heading I was using. It only takes a minute to edit ones user
details on 'KST ...........

John G4ZTR

Aka Grumpy of Colchester





1.9 to 2m Mesh Dish

Bob_G1ZJP
 

Hi All

I'm musing the idea of trying a mesh dish for 23cms & 13cms and would like to get as close to but not exceeding 2m.

Before I explore sources on the internet, does anyone reasonably close to Lincolnshire [try me to see if you're close enough], have one to sell please?

If no one wants to sell, then do others have any recommendations / sources of supply, please?

Thanks
Bob, G1ZJP / M1MHZ


dielectric plate polariser

Neil Smith G4DBN
 

I'm looking at making a dielectric plate circular polariser in a circular guide excited with a coaxial probe.  Assuming the probe is vertical when into the end of the waveguide, and the dielectric plate is at 45 degrees clockwise and produces a 90 degree lag, does that make RHCP or LHCP in space?

Am I right to assume that if I have another probe at 90 degrees to the first, it will work in the opposite sense CP?

If I have that right, how could I maximise the inter-port isolation?

Just idly wondering if I could use a rotating polariser plate to swap TX/RX polarisation when using a waveguide feed.

Most of the polarisers I've seen are just thin rectangular slabs with square edges, but I've also seen some with tapered transitions, either in thickness or with vee notches in the faces.  Is there any need to have a tapered transition for what is effectively a dielectric discontinuity anyway?

As usual, if there is an online resource or a book I should be reading, please point me at it.

Neil G4DBN


Just a suggestion

John Lemay
 

Yesterday in the 10GHz contest I spent a while trying (and failing) to work
a particular station. Just as I was giving up, it came to light that that G
station had crossed the boundary into GW and was portable about 15 degrees
off the heading I was using. It only takes a minute to edit ones user
details on 'KST ...........

John G4ZTR

Aka Grumpy of Colchester


Re: OSCAR 100 Dual feed dielectric lens

Neil Smith G4DBN
 

The illumination with an open tube will not be optimal, but depending how deep your dish is (F/D) it should only be a few dB down.  I can't find the pattern plots of open circular guide, might be on W1GHZ or somewhere?

Neil G4DBN

On 29/07/2019 12:00, Adrian G4AZS wrote:
"Hello Adrian, look here some info from PE1CKK":

Thanks Jerry, very useful.

"Whether a 0.02 loss tangent matters for a short-ish lens is an interesting question.  It is a bit better than dry wood, but not much"!

Yes, this is a whole new field for me, and I have no feel for what such figures mean in the context of what I am trying to achieve. I can see that Nylon isn't going to be the best choice, but it's a start.

Worst case would be having an open waveguide with no attempt at matching it to free space / efficiently illuminating the dish. Will any signal be detected with that at the focal point of the dish? If so, then any improvement from the addition of a lens will be observable. Will the quality of the lens (accuracy of dimensions / loss tangent)  be the defining factor, or more general considerations of permittivity and shape?

As an analogy, if I wanted to make an optical lens to focus the sun for heating purposes, I could probably achieve that by trial and error using simple tools and materials. On the other hand, if I wanted to make a telescope to read a distant notice, that would be a whole different challenge. I'm not sure where the dielectric lens project would be placed on a line between those two extremes - I'm hoping it might be closer to the first example.

"Useful table of complex permittivity (εr, tan(δ)) versus absolute temperature for microwave dielectrics can be found here": https://www.researchgate.net/publication/3130152_Complex_permittivity_measurements_of_common_plastics_over_variable_temperatures

Very interesting - not just for the table, but also the comments on measurement techniques and variables.
Fascinating that whilst for all of the materials the tangent loss generally increases with temperature, the changes in permittivity with temperature vary considerably from material to material. (if I am reading it correctly)

Adrian
G4AZS


Re: OSCAR 100 Dual feed dielectric lens

Neil Smith G4DBN
 

Hi Adrian, probably the "right" approach is to do a model using one of the EM solvers like CST, HFSS (if you have $$$$$$ or a friend with a copy and spare compute time!) or OpenEMS if you have the time to work it out.  Permittivity is important when you are calculating the pattern that will be produced.  Ultimately, the lens is there to give a decent match to the required illumination taper on the dish surface.  Most of the lenses used so far to match round waveguide to dishes have been flat, conical or stepped, but with CNC machines, complex compound tapers and asymmetric lens designs are perfectly possible.  The student version of CST has some limitations in terms of model size, but it works very well. OpenEMS is free/open and the only limitation is the painful learning curve and the amount of compute resource you have available to chuck at it.  Some of my models have taken 18 hours to calculate. I need to retire so I can do more of this interesting stuff.

I tried UHMWPE (which I bought to use as a bearing material for the elevation pivot for a 2.4m mesh dish!) as a lens material.  It machines well, but like all the softer engineering plastics, getting really sharp features and good surface finish is challenging when compared with things like acetal (useless for RF) and cross-linked polystyrene. I couldn't see any difference between the UHMWPE, Rexolite and PTFE in terms of performance, but I had to modify the shapes to suite the slightly different dielectric constants to keep the same illumination taper.

This pic is a one inch Rexolite rod turned at 1000rpm in a collet using a new 0.8mm corner-radius polished carbide positive-rake insert designed for aluminium.  The parallel section is 20mm diameter.  Surface finish is reasonable just using the insert, as you can see in the pic.  For perfectionists, a bit of fine Scotchbrite and a drop of paraffin as lube gives a glass-like polish. I like my things shiny, although the RF doesn't care.

Neil G4DBN

On 29/07/2019 12:00, Adrian G4AZS wrote:
"Hello Adrian, look here some info from PE1CKK":

Thanks Jerry, very useful.

"Whether a 0.02 loss tangent matters for a short-ish lens is an interesting question.  It is a bit better than dry wood, but not much"!

Yes, this is a whole new field for me, and I have no feel for what such figures mean in the context of what I am trying to achieve. I can see that Nylon isn't going to be the best choice, but it's a start.

Worst case would be having an open waveguide with no attempt at matching it to free space / efficiently illuminating the dish. Will any signal be detected with that at the focal point of the dish? If so, then any improvement from the addition of a lens will be observable. Will the quality of the lens (accuracy of dimensions / loss tangent)  be the defining factor, or more general considerations of permittivity and shape?

As an analogy, if I wanted to make an optical lens to focus the sun for heating purposes, I could probably achieve that by trial and error using simple tools and materials. On the other hand, if I wanted to make a telescope to read a distant notice, that would be a whole different challenge. I'm not sure where the dielectric lens project would be placed on a line between those two extremes - I'm hoping it might be closer to the first example.

"Useful table of complex permittivity (εr, tan(δ)) versus absolute temperature for microwave dielectrics can be found here": https://www.researchgate.net/publication/3130152_Complex_permittivity_measurements_of_common_plastics_over_variable_temperatures

Very interesting - not just for the table, but also the comments on measurement techniques and variables.
Fascinating that whilst for all of the materials the tangent loss generally increases with temperature, the changes in permittivity with temperature vary considerably from material to material. (if I am reading it correctly)

Adrian
G4AZS


Re: OSCAR 100 Dual feed dielectric lens

Adrian G4AZS
 

"Hello Adrian, look here some info from PE1CKK":
http://www.hybridpretender.nl/

Thanks Jerry, very useful.

"Whether a 0.02 loss tangent matters for a short-ish lens is an interesting question.  It is a bit better than dry wood, but not much"!

Yes, this is a whole new field for me, and I have no feel for what such figures mean in the context of what I am trying to achieve. I can see that Nylon isn't going to be the best choice, but it's a start.

Worst case would be having an open waveguide with no attempt at matching it to free space / efficiently illuminating the dish. Will any signal be detected with that at the focal point of the dish? If so, then any improvement from the addition of a lens will be observable. Will the quality of the lens (accuracy of dimensions / loss tangent)  be the defining factor, or more general considerations of permittivity and shape?

As an analogy, if I wanted to make an optical lens to focus the sun for heating purposes, I could probably achieve that by trial and error using simple tools and materials. On the other hand, if I wanted to make a telescope to read a distant notice, that would be a whole different challenge. I'm not sure where the dielectric lens project would be placed on a line between those two extremes - I'm hoping it might be closer to the first example.

"Useful table of complex permittivity (εr, tan(δ)) versus absolute temperature for microwave dielectrics can be found here": https://www.researchgate.net/publication/3130152_Complex_permittivity_measurements_of_common_plastics_over_variable_temperatures

Very interesting - not just for the table, but also the comments on measurement techniques and variables.
Fascinating that whilst for all of the materials the tangent loss generally increases with temperature, the changes in permittivity with temperature vary considerably from material to material. (if I am reading it correctly)

Adrian
G4AZS

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