Date   

24GHz Horn Optimisation

Chris Bartram G4DGU
 

Hello Neil

I'm just embarking on machining some coax-input feedhorns and waveguide transitions to use with these Wavelab units on 24 GHz, but I don't have anything I can use to check the return loss of the transitions or horns. I can make up a 20 dB cross-coupler in waveguide, but while I can sort-of use that with my spectrum analyser as detector, assuming my best 50 ohm load looks vaguely resistive at that frequency, I can't think how to check a coax-fed feedhorn.

Without access to a 24GHz-capable VNA and the right connectors, obviously.

It is just a question of modelling it to get close and then trimming for maximum smoke on TX and use cold sky versus moon/sun noise to verify that it is working right?      Is there some magic bit of testgear I can make or obtain to get the thing tuned spot on and remove any uncertainty?
I went through exactly that problem in the late 2000s when I was developing a feed for my then 2.4m dish. The basic design was conceived on paper and optimised with the aid of a simulation tool to which I used have access.

My solution FWIW was to find a couple of measurement quality directional couplers going cheap at a Roundtable. Not cross couplers, but broadside coupled designs: cross couplers are OK, but it's more difficult to get good directivity the 20dB level. From memory the coupling losses of mine are 20 and 30dB. ISTR they were made by Flann. There is design info. available I was also able to locate a couple of 3.5mm - coax adaptors, a couple of WG loads and courtesy of the late G3GNR, a tunable WG20 Gunn source. The difficult thing was to find a good 3.5mm coax termination. I did, but my lips are sealed as to the source. All I will say is that it was a rep. who like me has since retired!

Incidentally, there is  range of affordable 25GHz SMA connectors made by Emerson.

It's always worth having the ability to look at things out-of-band. It can show a lot of potential problems.

My own 24 GHz system uses WG20 and a Rellcom TR relay. I did use a coax system initially, but it didn't work as well as the current WG system.

Hope that's useful.

Chris G4DGU


Re: Original NanoVNA a waste of money

geoffrey pike
 

Indeed it's a useful tool, but so far they are all a bit too slow to tune anything with but i agree Alberto has done
a fantastic job with the Pluto
Geoff
GI0GDP


On Saturday, 20 March 2021, 16:23:01 GMT, Paul G4KZY <paul.g4kzy@...> wrote:


For higher frequencies, and to use with your directional couplers you could dig out your ADALM Pluto.

Alberto's SATSAGEN software is really very useful.

73,

Paul


Re: New MGM Modes on Beacons

Andy G4JNT
 

Yes, my thought behind doing this was FST4/FST4W  as a replacement for a WSPR beacon.



Virus-free. www.avg.com


On Sat, 20 Mar 2021 at 09:26, Bo, OZ2M <groups.io@...> wrote:
Good article! I think it was Bill, G4WJS, who wrote somewhere that the driver for the Gaussian keying was the crowed segments on the HF bands and use of spectrum. On VUSHF this is probably not an issue. The use of Gaussian keying requires a slightly wider FFT BW causing a S/N loss of a few 1/10 dB.

Back in spring 2018 Rolf, DK7FU, contacted me about the key click from DB0HRF, 2 m, that disturbed the DR9A contest group 172 km away. I made and installed a new S/W on the AD9912 driver that is able to perform linear intermediate steps when shifting from one tone to the next. We eventually settled for four intermediate steps. The steps reduced the key clicks by ~12 dB. More steps did not provide any significant difference. With 100 steps the signal sounded like a slide guitar straight out of Nashville. 100 steps also fooled PI-RX so this was not feasible at all.
BTW: if you ever get near Frankfurt a visit to the site of DB0HRF is worthwhile: https://taunus.info/angebote/natur-und-erlebnis/berge-und-felsen/grosser-feldberg/905/ The beacon on 2 m uses the "small" red-white omni-directional antenna.

I doubt that K = 1 modes will be successful on high VHF and USHF.

Bo
www.rudius.net/oz2m :: www.rfzero.net






Re: Original NanoVNA a waste of money

Paul G4KZY
 

For higher frequencies, and to use with your directional couplers you could dig out your ADALM Pluto.

Alberto's SATSAGEN software is really very useful.

73,

Paul


Re: Testing return loss of 24 GHz antennas and transitions

Neil Smith G4DBN
 

Ta, I had a look in my box of tuning bits and found some silver plated tuning screws with collars and locknuts. Can't recall where from but they are in sealed plastic pockets and look rather nice.  Extremely fine thread on them, looks like they are intended for tuning cavity resonators.  Bit of a waste to use them for this application. I also found a packet of screws with sapphire rod ends, ditto. Also found a few very small silver plated screws of unknown thread though. They could be 10BA, a bit over 1.6 mm diameter and look to be about 72tpi. I need to get some thread wires and a micrometer on them to be sure. They might be perfect for the 24 GHz bits I need immediately, but I'll bear in mind the offer.

Neil G4DBN

On 20/03/2021 12:00, Paul G8AQA via groups.io wrote:
Hi Neil,

I have a quantity of 2mm tuning screws salvaged from 23GHz equipment. They have a locking nut and square section lockwasher. Let me know if you want any.

73
Paul G8AQA

On 20/03/2021 11:03, Neil Smith G4DBN wrote:
I can certainly measure return loss up to 10 GHz in coax with a reasonable degree of precision, using some good SMA directioinal couplers or waveguide cross-couplers, and on 3.4, my NanoVNAv2plus4 and PocketVNA work very well and seem to agree with each other and with measurements using some HP directional couplers. I've made waveguide couplers up to 47 GHz, it's just that coax at 24 G is stretching me a bit.

It's simple enough to run a simulation in OpenEMS to find out the best balance of position, length, diameter and profile of the probe to get the desired return loss and bandwidth. The bandwidth does seem to come out right in the real thing, although defining the exact end of the PTFE insulation where it is trimmed does lead to a bit of uncertainty about the centre frequency.

I try to avoid tuning screws for aesthetic reasons, but that does lead to a lot of filing of the probes. I might relent, perhaps using sapphire rods mounted on screws, or threaded screws made from Rexolite, so there is no issue with contact corrosion. On some of the aluminium 3.4 GHz Super-VE4MA horns I made with welded backplates, I added a threaded tuning rod also made from aluminium.  That seemed a reasonable solution to prevent corrosion.

Using a fairly fat probe certainly helps to increase the bandwidth of the transition, at the cost of a lower peak return loss, but I guess anything over 17 dB or so is good enough?

Neil G4DBN


On 20/03/2021 04:49, Alan Beard via groups.io wrote:
Hi Neil,

This is why I was looking at broadband waveguide to coax transitions
last year as I wanted a "no tune" design, a 23cm feed horn for my 2m dish.
Preferably with enough bandwidth to be useful at 13cm.
Also, I don't care which face the coax connector is on.

I ended up with this DUBUS design, which I built.

Also, for 3.4GHz I have a Cross-bar transition (circ 1950). But nowhere can
I find any design details ie. how broadband is it?

Alan VK2ZIW


On Fri, 19 Mar 2021 20:09:18 +0000, Neil Smith G4DBN wrote
I'm just embarking on machining some coax-input feedhorns and
waveguide transitions to use with these Wavelab units on 24 GHz, but
I don't have anything I can use to check the return loss of the
transitions or horns. I can make up a 20 dB cross-coupler in
waveguide, but while I can sort-of use that with my spectrum
analyser as detector, assuming my best 50 ohm load looks vaguely
resistive at that frequency, I can't think how to check a coax-fed feedhorn.

Without access to a 24GHz-capable VNA and the right connectors, obviously.

It is just a question of modelling it to get close and then trimming
for maximum smoke on TX and use cold sky versus moon/sun noise to
verify that it is working right?      Is there some magic bit of
testgear I can make or obtain to get the thing tuned spot on and
remove any uncertainty?

I'm thinking of using a 2.92 mm connector with a hermetic seal
feedthru and a solid silver probe, because why not. They seem to be
cheaper than
3.5mm or high-end SMAs. That much Sterling silver is about 10p.

It would be SO much easier with a waveguide launch PA/LNA and w/g
relay, wouldn't it...

Neil G4DBN






Re: Testing return loss of 24 GHz antennas and transitions

Paul G8AQA
 

Neil,

I have 2 couplers from Macom. -17.5dB. One port terminated. 3.5mm connectors. No idea of the spec as it was probably military radar.  It could well be useful.  You are welcome to borrow one to play with. Maybe there is someone who could characterise it for us.

73
Paul G8AQA

On 20/03/2021 11:03, Neil Smith G4DBN wrote:
I can certainly measure return loss up to 10 GHz in coax with a reasonable degree of precision, using some good SMA directioinal couplers or waveguide cross-couplers, and on 3.4, my NanoVNAv2plus4 and PocketVNA work very well and seem to agree with each other and with measurements using some HP directional couplers. I've made waveguide couplers up to 47 GHz, it's just that coax at 24 G is stretching me a bit.

It's simple enough to run a simulation in OpenEMS to find out the best balance of position, length, diameter and profile of the probe to get the desired return loss and bandwidth. The bandwidth does seem to come out right in the real thing, although defining the exact end of the PTFE insulation where it is trimmed does lead to a bit of uncertainty about the centre frequency.

I try to avoid tuning screws for aesthetic reasons, but that does lead to a lot of filing of the probes. I might relent, perhaps using sapphire rods mounted on screws, or threaded screws made from Rexolite, so there is no issue with contact corrosion. On some of the aluminium 3.4 GHz Super-VE4MA horns I made with welded backplates, I added a threaded tuning rod also made from aluminium.  That seemed a reasonable solution to prevent corrosion.

Using a fairly fat probe certainly helps to increase the bandwidth of the transition, at the cost of a lower peak return loss, but I guess anything over 17 dB or so is good enough?

Neil G4DBN


On 20/03/2021 04:49, Alan Beard via groups.io wrote:
Hi Neil,

This is why I was looking at broadband waveguide to coax transitions
last year as I wanted a "no tune" design, a 23cm feed horn for my 2m dish.
Preferably with enough bandwidth to be useful at 13cm.
Also, I don't care which face the coax connector is on.

I ended up with this DUBUS design, which I built.

Also, for 3.4GHz I have a Cross-bar transition (circ 1950). But nowhere can
I find any design details ie. how broadband is it?

Alan VK2ZIW


On Fri, 19 Mar 2021 20:09:18 +0000, Neil Smith G4DBN wrote
I'm just embarking on machining some coax-input feedhorns and
waveguide transitions to use with these Wavelab units on 24 GHz, but
I don't have anything I can use to check the return loss of the
transitions or horns. I can make up a 20 dB cross-coupler in
waveguide, but while I can sort-of use that with my spectrum
analyser as detector, assuming my best 50 ohm load looks vaguely
resistive at that frequency, I can't think how to check a coax-fed feedhorn.

Without access to a 24GHz-capable VNA and the right connectors, obviously.

It is just a question of modelling it to get close and then trimming
for maximum smoke on TX and use cold sky versus moon/sun noise to
verify that it is working right?      Is there some magic bit of
testgear I can make or obtain to get the thing tuned spot on and
remove any uncertainty?

I'm thinking of using a 2.92 mm connector with a hermetic seal
feedthru and a solid silver probe, because why not. They seem to be
cheaper than
3.5mm or high-end SMAs. That much Sterling silver is about 10p.

It would be SO much easier with a waveguide launch PA/LNA and w/g
relay, wouldn't it...

Neil G4DBN










Virus-free. www.avg.com


Re: Testing return loss of 24 GHz antennas and transitions

Paul G8AQA
 

Hi Neil,

I have a quantity of 2mm tuning screws salvaged from 23GHz equipment. They have a locking nut and square section lockwasher. Let me know if you want any.

73
Paul G8AQA

On 20/03/2021 11:03, Neil Smith G4DBN wrote:
I can certainly measure return loss up to 10 GHz in coax with a reasonable degree of precision, using some good SMA directioinal couplers or waveguide cross-couplers, and on 3.4, my NanoVNAv2plus4 and PocketVNA work very well and seem to agree with each other and with measurements using some HP directional couplers. I've made waveguide couplers up to 47 GHz, it's just that coax at 24 G is stretching me a bit.

It's simple enough to run a simulation in OpenEMS to find out the best balance of position, length, diameter and profile of the probe to get the desired return loss and bandwidth. The bandwidth does seem to come out right in the real thing, although defining the exact end of the PTFE insulation where it is trimmed does lead to a bit of uncertainty about the centre frequency.

I try to avoid tuning screws for aesthetic reasons, but that does lead to a lot of filing of the probes. I might relent, perhaps using sapphire rods mounted on screws, or threaded screws made from Rexolite, so there is no issue with contact corrosion. On some of the aluminium 3.4 GHz Super-VE4MA horns I made with welded backplates, I added a threaded tuning rod also made from aluminium.  That seemed a reasonable solution to prevent corrosion.

Using a fairly fat probe certainly helps to increase the bandwidth of the transition, at the cost of a lower peak return loss, but I guess anything over 17 dB or so is good enough?

Neil G4DBN


On 20/03/2021 04:49, Alan Beard via groups.io wrote:
Hi Neil,

This is why I was looking at broadband waveguide to coax transitions
last year as I wanted a "no tune" design, a 23cm feed horn for my 2m dish.
Preferably with enough bandwidth to be useful at 13cm.
Also, I don't care which face the coax connector is on.

I ended up with this DUBUS design, which I built.

Also, for 3.4GHz I have a Cross-bar transition (circ 1950). But nowhere can
I find any design details ie. how broadband is it?

Alan VK2ZIW


On Fri, 19 Mar 2021 20:09:18 +0000, Neil Smith G4DBN wrote
I'm just embarking on machining some coax-input feedhorns and
waveguide transitions to use with these Wavelab units on 24 GHz, but
I don't have anything I can use to check the return loss of the
transitions or horns. I can make up a 20 dB cross-coupler in
waveguide, but while I can sort-of use that with my spectrum
analyser as detector, assuming my best 50 ohm load looks vaguely
resistive at that frequency, I can't think how to check a coax-fed feedhorn.

Without access to a 24GHz-capable VNA and the right connectors, obviously.

It is just a question of modelling it to get close and then trimming
for maximum smoke on TX and use cold sky versus moon/sun noise to
verify that it is working right?      Is there some magic bit of
testgear I can make or obtain to get the thing tuned spot on and
remove any uncertainty?

I'm thinking of using a 2.92 mm connector with a hermetic seal
feedthru and a solid silver probe, because why not. They seem to be
cheaper than
3.5mm or high-end SMAs. That much Sterling silver is about 10p.

It would be SO much easier with a waveguide launch PA/LNA and w/g
relay, wouldn't it...

Neil G4DBN










Virus-free. www.avg.com


Re: Testing return loss of 24 GHz antennas and transitions

Neil Smith G4DBN
 

I can certainly measure return loss up to 10 GHz in coax with a reasonable degree of precision, using some good SMA directioinal couplers or waveguide cross-couplers, and on 3.4, my NanoVNAv2plus4 and PocketVNA work very well and seem to agree with each other and with measurements using some HP directional couplers. I've made waveguide couplers up to 47 GHz, it's just that coax at 24 G is stretching me a bit.

It's simple enough to run a simulation in OpenEMS to find out the best balance of position, length, diameter and profile of the probe to get the desired return loss and bandwidth. The bandwidth does seem to come out right in the real thing, although defining the exact end of the PTFE insulation where it is trimmed does lead to a bit of uncertainty about the centre frequency.

I try to avoid tuning screws for aesthetic reasons, but that does lead to a lot of filing of the probes. I might relent, perhaps using sapphire rods mounted on screws, or threaded screws made from Rexolite, so there is no issue with contact corrosion. On some of the aluminium 3.4 GHz Super-VE4MA horns I made with welded backplates, I added a threaded tuning rod also made from aluminium.  That seemed a reasonable solution to prevent corrosion.

Using a fairly fat probe certainly helps to increase the bandwidth of the transition, at the cost of a lower peak return loss, but I guess anything over 17 dB or so is good enough?

Neil G4DBN

On 20/03/2021 04:49, Alan Beard via groups.io wrote:
Hi Neil,

This is why I was looking at broadband waveguide to coax transitions
last year as I wanted a "no tune" design, a 23cm feed horn for my 2m dish.
Preferably with enough bandwidth to be useful at 13cm.
Also, I don't care which face the coax connector is on.

I ended up with this DUBUS design, which I built.

Also, for 3.4GHz I have a Cross-bar transition (circ 1950). But nowhere can
I find any design details ie. how broadband is it?

Alan VK2ZIW


On Fri, 19 Mar 2021 20:09:18 +0000, Neil Smith G4DBN wrote
I'm just embarking on machining some coax-input feedhorns and
waveguide transitions to use with these Wavelab units on 24 GHz, but
I don't have anything I can use to check the return loss of the
transitions or horns. I can make up a 20 dB cross-coupler in
waveguide, but while I can sort-of use that with my spectrum
analyser as detector, assuming my best 50 ohm load looks vaguely
resistive at that frequency, I can't think how to check a coax-fed feedhorn.

Without access to a 24GHz-capable VNA and the right connectors, obviously.

It is just a question of modelling it to get close and then trimming
for maximum smoke on TX and use cold sky versus moon/sun noise to
verify that it is working right?      Is there some magic bit of
testgear I can make or obtain to get the thing tuned spot on and
remove any uncertainty?

I'm thinking of using a 2.92 mm connector with a hermetic seal
feedthru and a solid silver probe, because why not. They seem to be
cheaper than
3.5mm or high-end SMAs. That much Sterling silver is about 10p.

It would be SO much easier with a waveguide launch PA/LNA and w/g
relay, wouldn't it...

Neil G4DBN


Re: MGM Beacon History

Bo, OZ2M
 

OZ7IGY did not start with MGM, JT65B2, until 30 Oct. 2012. There must be other beacons in-between 2005 and 2012.

Bo
www.rudius.net/oz2m :: www.rfzero.net


Re: New MGM Modes on Beacons

Bo, OZ2M
 

Good article! I think it was Bill, G4WJS, who wrote somewhere that the driver for the Gaussian keying was the crowed segments on the HF bands and use of spectrum. On VUSHF this is probably not an issue. The use of Gaussian keying requires a slightly wider FFT BW causing a S/N loss of a few 1/10 dB.

Back in spring 2018 Rolf, DK7FU, contacted me about the key click from DB0HRF, 2 m, that disturbed the DR9A contest group 172 km away. I made and installed a new S/W on the AD9912 driver that is able to perform linear intermediate steps when shifting from one tone to the next. We eventually settled for four intermediate steps. The steps reduced the key clicks by ~12 dB. More steps did not provide any significant difference. With 100 steps the signal sounded like a slide guitar straight out of Nashville. 100 steps also fooled PI-RX so this was not feasible at all.
BTW: if you ever get near Frankfurt a visit to the site of DB0HRF is worthwhile: https://taunus.info/angebote/natur-und-erlebnis/berge-und-felsen/grosser-feldberg/905/ The beacon on 2 m uses the "small" red-white omni-directional antenna.

I doubt that K = 1 modes will be successful on high VHF and USHF.

Bo
www.rudius.net/oz2m :: www.rfzero.net


Re: Testing return loss of 24 GHz antennas and transitions

Alan Beard
 

Hi Neil,

This is why I was looking at broadband waveguide to coax transitions
last year as I wanted a "no tune" design, a 23cm feed horn for my 2m dish.
Preferably with enough bandwidth to be useful at 13cm.
Also, I don't care which face the coax connector is on.

I ended up with this DUBUS design, which I built.

Also, for 3.4GHz I have a Cross-bar transition (circ 1950). But nowhere can
I find any design details ie. how broadband is it?

Alan VK2ZIW


On Fri, 19 Mar 2021 20:09:18 +0000, Neil Smith G4DBN wrote
I'm just embarking on machining some coax-input feedhorns and
waveguide transitions to use with these Wavelab units on 24 GHz, but
I don't have anything I can use to check the return loss of the
transitions or horns. I can make up a 20 dB cross-coupler in
waveguide, but while I can sort-of use that with my spectrum
analyser as detector, assuming my best 50 ohm load looks vaguely
resistive at that frequency, I can't think how to check a coax-fed feedhorn.

Without access to a 24GHz-capable VNA and the right connectors, obviously.

It is just a question of modelling it to get close and then trimming
for maximum smoke on TX and use cold sky versus moon/sun noise to
verify that it is working right?      Is there some magic bit of
testgear I can make or obtain to get the thing tuned spot on and
remove any uncertainty?

I'm thinking of using a 2.92 mm connector with a hermetic seal
feedthru and a solid silver probe, because why not. They seem to be
cheaper than
3.5mm or high-end SMAs. That much Sterling silver is about 10p.

It would be SO much easier with a waveguide launch PA/LNA and w/g
relay, wouldn't it...

Neil G4DBN


---------------------------------------------------
Alan VK2ZIW
Before the Big Bang, God, Sela.
OpenWebMail 2.53, nothing in the cloud.


Re: Testing return loss of 24 GHz antennas and transitions

Neil Smith G4DBN
 

I have a 20 to 26 GHz YIG oscillator that makes a stonking great big signal and can sweep across a wide range. I made a sampler with two sections of copper semirigid with the sides of the sheath machined away, rejoined and soldered. That had enough coupling to get a decent signal level into my specan.  Just wondering if I could make a better version of that with a suitable terminating load, or perhaps machine up a coupler body and use some of those spiffy threaded SMAs I got from Paul G8AQA to make up an teensy air dielectric  directional coupler. With a few screws, I could probably get reasonable directivity. I have a couple of SMA loads that are rated to 26.5 GHz, although I think one of them is a 3.5.  I keep it for Sunday Best.

I found a nice SMA 26.5 GHz directional coupler on ebay but it is $$$$$$$$$.  I'm not looking at instrument-quality here, so maybe I'll dig out the twinned coax coupler and see if it has any directivity with the decent load on it.

Easy enough to machine up a decent waveguide coupler, but I see there are a few for sale as well if I'm feeling lazy.

The thought on using silver for the probe is that it's a lot nicer to machine than copper, although I don't know if I'd get away with a thermal shrink-fit or if I'd have to use soft solder. It would be fun to machine up some 134 or 241 GHz feedhorns from a cast silver master, although once I get my explosives precursors and poisons licence, the first job after a bit of anodising will be electroforming some corrugated SHF horns on an aluminium machined mandrels, then dissolving the aluminium away.

The other thought I had was whether a slotted line sampler is feasible in WR42. Slitting a 0.5mm slot into the broad face of a bit of waveguide after thinning the top, then making a carriage and slider arrangement would be a bit of fun to make.  Just need a suitable detector. My HP33330B runs out of puff at around 20 GHz. Directional coupler seems a lot simpler.

I'm trying to work out the downside of just tuning the transition or horn probe for maximum transmitted signal, then verifying sun/moon noise matches expectations

Neil G4DBN

On 19/03/2021 21:34, Mark GM4ISM via groups.io wrote:
Neil,

Amongst the things in my junkbox  are some nice Flann broadwall WG20 directional couplers and once in the WG domain I can measure return loss to a reasonable accuracy (Directivity  is 35dBmin)

Even with my best commercial coax transitions, the measurement uncertainly becomes  interesting.

 I have a 26GHz 50 ohm calibrated load  which helps  but without a proper coaxial S Parameter test set and Scalar  analyser,  I struggle.

The only mechanism I have left but not yet explored at 24GHz, is wobbulation.

A non-directional coupler  (signal sampler) and detector with a resolution of 0.1dB is all that needed. Absolute accuracy is unimportant

 You either change the sample point along the transmission line ( difficult in coax) or sweep over a suitable frequency range

 The resultant  amplitude vs frequency ( or distance) response will  vary,   FFT analysis will give you DTF / TDR*  information / antenna return loss information. You can do 'qualitative'  FFT anaylsis in your head :)  You wont be able to  determine accurate DTF  info this way but you can optimise antennas.  The technique does not lend itself well to very short transmission lines

 To calibrate this, ideally  you need a good know 50 Ohm load. With that I can probably help by 'matching' my good reference to a secondary load with a similar response.

 I believe I could achieve a secondary and traceable measurement system with a directivity of at least 25dB.  Not great but adequate.

On the subject of silver components, if you need silver, i have plenty and can cast into large ish  rough shapes suitable for your machining  skills, (Delft Clay casting method)

 I have about 300g of silver 'in stock' for casting, so there is scope for experimentation.

 There are few component that would benefit greatly from being made of silver  but if you find a need, give me a call.

 I can cast gold too of course but that is really not very cost effective. I don't have much surplus 18k + gold either :)

Good luck..  This is a field that few amateurs master with reasonable accuracy but it is possible  at reasonable cost, with effort, even at 24GHz.

Mark GM4ISM

* Note that the terms DTF (Distance to fault) and TDR (Time domain Reflectometry) are often interchangeable but there are are differences ,  associated with the way the data is measured. Measurement  parameters are  important  for these techniques and it is easy to  get things wrong and 'contaminate' results with errors  that are not obvious.





On 19/03/2021 20:09, Neil Smith G4DBN wrote:
I'm just embarking on machining some coax-input feedhorns and waveguide transitions to use with these Wavelab units on 24 GHz, but I don't have anything I can use to check the return loss of the transitions or horns. I can make up a 20 dB cross-coupler in waveguide, but while I can sort-of use that with my spectrum analyser as detector, assuming my best 50 ohm load looks vaguely resistive at that frequency, I can't think how to check a coax-fed feedhorn.

Without access to a 24GHz-capable VNA and the right connectors, obviously.

It is just a question of modelling it to get close and then trimming for maximum smoke on TX and use cold sky versus moon/sun noise to verify that it is working right?      Is there some magic bit of testgear I can make or obtain to get the thing tuned spot on and remove any uncertainty?

I'm thinking of using a 2.92 mm connector with a hermetic seal feedthru and a solid silver probe, because why not. They seem to be cheaper than 3.5mm or high-end SMAs. That much Sterling silver is about 10p.

It would be SO much easier with a waveguide launch PA/LNA and w/g relay, wouldn't it...

Neil G4DBN






Re: Testing return loss of 24 GHz antennas and transitions

Mark GM4ISM
 

Neil,

Amongst the things in my junkbox  are some nice Flann broadwall WG20 directional couplers and once in the WG domain I can measure return loss to a reasonable accuracy (Directivity  is 35dBmin)

Even with my best commercial coax transitions, the measurement uncertainly becomes  interesting.

 I have a 26GHz 50 ohm calibrated load  which helps  but without a proper coaxial S Parameter test set and Scalar  analyser,  I struggle.

The only mechanism I have left but not yet explored at 24GHz, is wobbulation.

A non-directional coupler  (signal sampler) and detector with a resolution of 0.1dB is all that needed. Absolute accuracy is unimportant

 You either change the sample point along the transmission line ( difficult in coax) or sweep over a suitable frequency range

 The resultant  amplitude vs frequency ( or distance) response will  vary,   FFT analysis will give you DTF / TDR*  information / antenna return loss information. You can do 'qualitative'  FFT anaylsis in your head :)  You wont be able to  determine accurate DTF  info this way but you can optimise antennas.  The technique does not lend itself well to very short transmission lines

 To calibrate this, ideally  you need a good know 50 Ohm load. With that I can probably help by 'matching' my good reference to a secondary load with a similar response.

 I believe I could achieve a secondary and traceable measurement system with a directivity of at least 25dB.  Not great but adequate.

On the subject of silver components, if you need silver, i have plenty and can cast into large ish  rough shapes suitable for your machining  skills, (Delft Clay casting method)

 I have about 300g of silver 'in stock' for casting, so there is scope for experimentation.

 There are few component that would benefit greatly from being made of silver  but if you find a need, give me a call.

 I can cast gold too of course but that is really not very cost effective. I don't have much surplus 18k + gold either :)

Good luck..  This is a field that few amateurs master with reasonable accuracy but it is possible  at reasonable cost, with effort, even at 24GHz.

Mark GM4ISM

* Note that the terms DTF (Distance to fault) and TDR (Time domain Reflectometry) are often interchangeable but there are are differences ,  associated with the way the data is measured. Measurement  parameters are  important  for these techniques and it is easy to  get things wrong and 'contaminate' results with errors  that are not obvious.

On 19/03/2021 20:09, Neil Smith G4DBN wrote:
I'm just embarking on machining some coax-input feedhorns and waveguide transitions to use with these Wavelab units on 24 GHz, but I don't have anything I can use to check the return loss of the transitions or horns. I can make up a 20 dB cross-coupler in waveguide, but while I can sort-of use that with my spectrum analyser as detector, assuming my best 50 ohm load looks vaguely resistive at that frequency, I can't think how to check a coax-fed feedhorn.

Without access to a 24GHz-capable VNA and the right connectors, obviously.

It is just a question of modelling it to get close and then trimming for maximum smoke on TX and use cold sky versus moon/sun noise to verify that it is working right?      Is there some magic bit of testgear I can make or obtain to get the thing tuned spot on and remove any uncertainty?

I'm thinking of using a 2.92 mm connector with a hermetic seal feedthru and a solid silver probe, because why not. They seem to be cheaper than 3.5mm or high-end SMAs. That much Sterling silver is about 10p.

It would be SO much easier with a waveguide launch PA/LNA and w/g relay, wouldn't it...

Neil G4DBN




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Testing return loss of 24 GHz antennas and transitions

Neil Smith G4DBN
 

I'm just embarking on machining some coax-input feedhorns and waveguide transitions to use with these Wavelab units on 24 GHz, but I don't have anything I can use to check the return loss of the transitions or horns. I can make up a 20 dB cross-coupler in waveguide, but while I can sort-of use that with my spectrum analyser as detector, assuming my best 50 ohm load looks vaguely resistive at that frequency, I can't think how to check a coax-fed feedhorn.

Without access to a 24GHz-capable VNA and the right connectors, obviously.

It is just a question of modelling it to get close and then trimming for maximum smoke on TX and use cold sky versus moon/sun noise to verify that it is working right?      Is there some magic bit of testgear I can make or obtain to get the thing tuned spot on and remove any uncertainty?

I'm thinking of using a 2.92 mm connector with a hermetic seal feedthru and a solid silver probe, because why not. They seem to be cheaper than 3.5mm or high-end SMAs. That much Sterling silver is about 10p.

It would be SO much easier with a waveguide launch PA/LNA and w/g relay, wouldn't it...

Neil G4DBN


Re: Original NanoVNA a waste of money

Andy G4JNT
 

Yes, agreed.   For higher frequencies I have several directional couplers for DC to 12GHz and use a synth + spec analyser as a makeshift scalar return loss measurement.   A PRN based  noise source and mixer gives a wideband signal for some applications



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On Fri, 19 Mar 2021 at 17:46, geoffrey pike via groups.io <gi0gdp=yahoo.co.uk@groups.io> wrote:
Well there you go, i do the opposite and haven't switched my SAQ in over a year (i suppose when i do there will be aggro getting it going again)
But the SAA-2 really is way ahead in frequency perhaps not the best of software support however
I think the SAQ needs to extend a bit in frequency to make it attractive to new users
Just my 3ds worth
cheers
Geoff
GI0GDP



On Friday, 19 March 2021, 17:29:50 GMT, Andy G4JNT <andy.g4jnt@...> wrote:


I bought one of the original NanoVNAs not long afte rthay came out, and initially it worked OK.  Put it away and hadn't used in for perhaps nearly a year.
When I came to use it today, obvs. the battery needed charging, but the touchscreen ignores most of my presses, and those it does interpret it gets wrong then goes into a huff
The manual slider doesn't respond
 
Don't think I'll ever get one again, no matter how much better the new ones are.   

Not sure whether to put a hammer through it or dismantle to see what's inside.
A hammer would be more satisfying.

Meanwhile, the job I wanted it for, the DG8SAQ did the job perfectly, with a much nicer display.  Just meant taking the laptop and the 'SAQ outside - so wasn't so convenient.


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Re: Original NanoVNA a waste of money

geoffrey pike
 

Well there you go, i do the opposite and haven't switched my SAQ in over a year (i suppose when i do there will be aggro getting it going again)
But the SAA-2 really is way ahead in frequency perhaps not the best of software support however
I think the SAQ needs to extend a bit in frequency to make it attractive to new users
Just my 3ds worth
cheers
Geoff
GI0GDP



On Friday, 19 March 2021, 17:29:50 GMT, Andy G4JNT <andy.g4jnt@...> wrote:


I bought one of the original NanoVNAs not long afte rthay came out, and initially it worked OK.  Put it away and hadn't used in for perhaps nearly a year.
When I came to use it today, obvs. the battery needed charging, but the touchscreen ignores most of my presses, and those it does interpret it gets wrong then goes into a huff
The manual slider doesn't respond
 
Don't think I'll ever get one again, no matter how much better the new ones are.   

Not sure whether to put a hammer through it or dismantle to see what's inside.
A hammer would be more satisfying.

Meanwhile, the job I wanted it for, the DG8SAQ did the job perfectly, with a much nicer display.  Just meant taking the laptop and the 'SAQ outside - so wasn't so convenient.


Virus-free. www.avg.com


Original NanoVNA a waste of money

Andy G4JNT
 

I bought one of the original NanoVNAs not long afte rthay came out, and initially it worked OK.  Put it away and hadn't used in for perhaps nearly a year.
When I came to use it today, obvs. the battery needed charging, but the touchscreen ignores most of my presses, and those it does interpret it gets wrong then goes into a huff
The manual slider doesn't respond
 
Don't think I'll ever get one again, no matter how much better the new ones are.   

Not sure whether to put a hammer through it or dismantle to see what's inside.
A hammer would be more satisfying.

Meanwhile, the job I wanted it for, the DG8SAQ did the job perfectly, with a much nicer display.  Just meant taking the laptop and the 'SAQ outside - so wasn't so convenient.


Virus-free. www.avg.com


Re: HP vector network Analyser charity giveaway

Alan Melia
 

I'm surprised anyone noticed the difference !!
Alan
G3NYK

----- Original Message -----
Sent: Friday, March 19, 2021 2:01 PM
Subject: Re: [UKMicrowaves] HP vector network Analyser charity giveaway

BBC Traffic Report

East Anglia paralysed by mystery traffic jam.

73,

Alwyn G8DOH
_____________________________________________________

Alwyn Seeds, Director
SynOptika Ltd.,
114 Beaufort Street,
London,
SW3 6BU,
England.


SynOptika Ltd., Registered in England and Wales: No. 04606737
Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom.
_____________________________________________________


Re: HP vector network Analyser charity giveaway

alwyn.seeds1
 

BBC Traffic Report

East Anglia paralysed by mystery traffic jam.

73,

Alwyn G8DOH
_____________________________________________________

Alwyn Seeds, Director
SynOptika Ltd.,
114 Beaufort Street,
London,
SW3 6BU,
England.


SynOptika Ltd., Registered in England and Wales: No. 04606737
Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom.
_____________________________________________________


HP vector network Analyser charity giveaway

John Worsnop
 

Strictly buyer collects QTHR

First person to offer to make a £75 or larger donation to Medecins sans Frontieres (MSF) and then proves to me they've done it


Gets a boat anchor 1.3GHz Network Analyser kit - in working order + pdf manuals

Help someone in need and spare the VNA from rusting on my garage floor as I'm unlikely to ever use it again.

Consisting of:
HP8754A VNA
HP8750 Storage Normaliser
HP8502 Transmission/Reflection test set plus cables

email me direct, off reflector. john(at)g4bao.com
Reflector replies will be ignored 

73
John

2521 - 2540 of 64105