Date   

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


THz communication | Live webinar

i2NDT
 

I guess it might be interesting to attend this free webinar:
>>>> quote
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  • Channel measurements in the sub-THz region?

Our upcoming webinar explores Sub-terahertz and terahertz (THz) waves and offers you an overview on potential application areas.

When?

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registration link:
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best 73
de
i2NDT Claudio


Re: MGM Beacon History

DAVID G4ASR
 
Edited

Andy,   

I think you are correct regarding GB3VHF.  The Danish beacon-cluster OZ7IGY come a good second .       www.oz7igy.dk/

David G4ASR


Re: New MGM Modes on Beacons

Mike Lavelle K6ML
 

Andy,

Sorry, that was my mistake.   I mixed up ISCAT (which is unfortunately being deleted... it’s still being used for microwave aircraft scatter) with JT4 (which is alive and well).    In the last part quoted, I was not writing that JT64 was retired, just QRA64 (the parens only applied to QRA64).  

While I’m at it, my comment about which modes use hard vs Gaussian keying (and my quote from Joe that modes over 4 bits were hard keyed) was focused on microwave modes, so ignored FT8, which, as your writeup mentions does use Gaussian. 

I also agree with your statements about frequency multiplication amplifying spurs by 20 dB per decade (same as phase noise and FM noise) being a serious issue by at microwaves and even worse at millimeter waves.  Working at 122 GHz, with a 12,200x multiplication factor, I have managed to produce some awful spectra with serious spurs, FM and PN.   John Miles (KE5FX) suggested on his excellent website that a great way to find out how truely awful a VHF source can be is to use it as the reference input to a microwave ‘brick’ and then look at the multiplied spectrum at microwaves.   ‘Clean’ oscillatros can shown to be quite ‘dirty’ using this technique.        

It looks like translation loops (PLLs with mixers) may be a good solution to spurs, etc, at SHF/EHF.    

I don’t see a problem with using frac-N with MFSK ... the requirement is CPFSK, which PLLs do meet... the VCO waveform is not discontinuous, just not elegantly shaped FM.... and if the PLL loop bandwidth is low (but still at at least 10-20x the baud rate), the low pass filtering produces smooth keying.


Mike K6ML

Mike K6ML


Re: New MGM Modes on Beacons

Andy G4JNT
 

JT4 is still in the latest (a couple of days ago) 2.4.0 RC3 version.   It had better remain, as it's in quite widespread use on microwave beacons, being one of teh few modes capable of coping with really widespread scattering such as that from rainscatter on 10 and 24GHz

When I asked Joe about it a while back, he assured me that JT4 and JT65 would be kept for this purpose.   Beacon modulations can't be changed on the whim.



On Wed, 17 Mar 2021 at 02:00, Mike Lavelle K6ML <miclevel@...> wrote:
A few comments:

...; the earlier JT4 (which has unfortunately been declared 'obsolete' and removed from the latest release candidate), JT65 and QRA64 (also removed) do/did not use gaussian shaping).

- .


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Re: New MGM Modes on Beacons

Mike Lavelle K6ML
 

A few comments:

- not all of the new WSJT modes use gaussian shaped keying...  when I asked, K1JT replied that the modes with tone counts greater than 4 did not benefit from gaussian shaped keying (so, FST4, yes, Q65, no; the earlier JT4 (which has unfortunately been declared 'obsolete' and removed from the latest release candidate), JT65 and QRA64 (also removed) do/did not use gaussian shaping).

- gaussian shaping mainly helps cut down the transmitter sidebands (a good thing on crowded HF bands, and probably for a beacon, too).  it actually makes the decoder's task more difficult (more intersymbol interference from the 'smoothing' is the price for less 'splatter').   I suspect that the decoders for a gaussian keyed mode would be happier (if they had emotions :) with hard keyed modulation and probably are not (can't be) doing anything special to listen to gaussian keyers.

So, other than VLF and WSPR beacons, I suspect the gaussian keying is not providing benefit, nor being used in many modes.  I also believe that at microwave and above, there is no need to worry about it.


Re: New MGM Modes on Beacons

G8DQX list
 

If you think of the spurii as FM sidebands, then on multiplication by 2, for example, the modulation index (assuming it's very small) has doubled, thus a 6dB increase in level, and so forth.

HTH, 73, Stay Safe,

Robin, G8DQX

On 16/03/2021 17:53, Andy G4JNT wrote:
No, it doesn't work like that.   Visualise the multiplier as a hard limiter or zero crossing detector:

That -30dB 90MHz component adds to the 100MHz signal and periodically shifts the point at which the main 100MHz component crosses the zero threshold, resulting in a jitter on the limited output.  The resulting jitter then reappears as sidebands on the multiplied output.   You have to consider the total input, with spurii, in the time domain.

I can't supply the mathematical proof of the reason for squaring, or why it isn't any other order, but it's certainly there in practice and quite observable.

Andy


On Tue, 16 Mar 2021 at 17:46, Robin Szemeti - G1YFG <robin@...> wrote:
" When the RF is passed through a frequency multiplier these spurii increase in relative amplitude as the square of the multiplication factor"

I found this "interesting" as I would have thought that if you had say 100MHz at 0dBm and 90MHz spur at -30dBm ... and then whacked the signal through a x3 multiplier, by driving some MMIC or similar hard into clipping ... I would have expected the output to be swamped by the 100MHz signal, and the "weak" 90MHz signal to be effectively blocked, and thus removed from the output,  and by the time it had been through the output filter to pick up the 3rd harmonic, I would expect it to look very clean indeed.  I had always assumed that multiplier chains cleaned up the spurs, not made them worse. I shall ponder this further ...


On Tue, 16 Mar 2021 at 16:57, John Quarmby via groups.io <g3xdy=btinternet.com@groups.io> wrote:

Alwyn

I have not got hard numbers to hand, but I can compare it with the 23cm beacon, where the beacon is approximately 95dB above noise in 2.5kHz bandwidth and results in a rise in the apparent band noise of 5db when I beam at it on 1296.200. My LO and the beacon oscillator are almost identical, so probably each contributes the same amount of phase noise. I have a crystal notch filter in the 28MHz transverter IF to reduce the beacon signal level by about 50dB going into the K3.

The 13cm beacon is about 10dB weaker, there is no change in band noise at 2320.200 when I beam at it. There are no major spurs in the SSB/CW part of the band, but they are apparent in the beacon band. When we have got it on air again I will make some proper measurements.

73

John G3XDY

On 16/03/2021 13:19, alwyn.seeds1 wrote:
Dear John and Andy,

Getting DDS spurs low enough for beacon use must be quite a challenge. At work, all of our DDS based signal generators, including the pricey ones, have quite a few spurs at the -80 dBc level- the nuisance is that they do not have easily predictable frequencies. We moan to the manufacturers but I have not seen much improvement over the last decade.

John, what sort of phase noise numbers do you get from the GB3MHZ beacon?

Regards,

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.
_____________________________________________________


Virus-free. www.avast.com

--
Robin Szemeti - G1YFG


Re: New MGM Modes on Beacons

Dominique Dehays
 

Hi all ,


Yes my experiments show a 20 log N increase of spurs.
73
Dom


Re: New MGM Modes on Beacons

Andy G4JNT
 

No, it doesn't work like that.   Visualise the multiplier as a hard limiter or zero crossing detector:

That -30dB 90MHz component adds to the 100MHz signal and periodically shifts the point at which the main 100MHz component crosses the zero threshold, resulting in a jitter on the limited output.  The resulting jitter then reappears as sidebands on the multiplied output.   You have to consider the total input, with spurii, in the time domain.

I can't supply the mathematical proof of the reason for squaring, or why it isn't any other order, but it's certainly there in practice and quite observable.

Andy


On Tue, 16 Mar 2021 at 17:46, Robin Szemeti - G1YFG <robin@...> wrote:
" When the RF is passed through a frequency multiplier these spurii increase in relative amplitude as the square of the multiplication factor"

I found this "interesting" as I would have thought that if you had say 100MHz at 0dBm and 90MHz spur at -30dBm ... and then whacked the signal through a x3 multiplier, by driving some MMIC or similar hard into clipping ... I would have expected the output to be swamped by the 100MHz signal, and the "weak" 90MHz signal to be effectively blocked, and thus removed from the output,  and by the time it had been through the output filter to pick up the 3rd harmonic, I would expect it to look very clean indeed.  I had always assumed that multiplier chains cleaned up the spurs, not made them worse. I shall ponder this further ...


On Tue, 16 Mar 2021 at 16:57, John Quarmby via groups.io <g3xdy=btinternet.com@groups.io> wrote:

Alwyn

I have not got hard numbers to hand, but I can compare it with the 23cm beacon, where the beacon is approximately 95dB above noise in 2.5kHz bandwidth and results in a rise in the apparent band noise of 5db when I beam at it on 1296.200. My LO and the beacon oscillator are almost identical, so probably each contributes the same amount of phase noise. I have a crystal notch filter in the 28MHz transverter IF to reduce the beacon signal level by about 50dB going into the K3.

The 13cm beacon is about 10dB weaker, there is no change in band noise at 2320.200 when I beam at it. There are no major spurs in the SSB/CW part of the band, but they are apparent in the beacon band. When we have got it on air again I will make some proper measurements.

73

John G3XDY

On 16/03/2021 13:19, alwyn.seeds1 wrote:
Dear John and Andy,

Getting DDS spurs low enough for beacon use must be quite a challenge. At work, all of our DDS based signal generators, including the pricey ones, have quite a few spurs at the -80 dBc level- the nuisance is that they do not have easily predictable frequencies. We moan to the manufacturers but I have not seen much improvement over the last decade.

John, what sort of phase noise numbers do you get from the GB3MHZ beacon?

Regards,

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.
_____________________________________________________


Virus-free. www.avast.com


--
Robin Szemeti - G1YFG


Re: New MGM Modes on Beacons

Robin Szemeti - G1YFG
 

" When the RF is passed through a frequency multiplier these spurii increase in relative amplitude as the square of the multiplication factor"

I found this "interesting" as I would have thought that if you had say 100MHz at 0dBm and 90MHz spur at -30dBm ... and then whacked the signal through a x3 multiplier, by driving some MMIC or similar hard into clipping ... I would have expected the output to be swamped by the 100MHz signal, and the "weak" 90MHz signal to be effectively blocked, and thus removed from the output,  and by the time it had been through the output filter to pick up the 3rd harmonic, I would expect it to look very clean indeed.  I had always assumed that multiplier chains cleaned up the spurs, not made them worse. I shall ponder this further ...


On Tue, 16 Mar 2021 at 16:57, John Quarmby via groups.io <g3xdy=btinternet.com@groups.io> wrote:

Alwyn

I have not got hard numbers to hand, but I can compare it with the 23cm beacon, where the beacon is approximately 95dB above noise in 2.5kHz bandwidth and results in a rise in the apparent band noise of 5db when I beam at it on 1296.200. My LO and the beacon oscillator are almost identical, so probably each contributes the same amount of phase noise. I have a crystal notch filter in the 28MHz transverter IF to reduce the beacon signal level by about 50dB going into the K3.

The 13cm beacon is about 10dB weaker, there is no change in band noise at 2320.200 when I beam at it. There are no major spurs in the SSB/CW part of the band, but they are apparent in the beacon band. When we have got it on air again I will make some proper measurements.

73

John G3XDY

On 16/03/2021 13:19, alwyn.seeds1 wrote:
Dear John and Andy,

Getting DDS spurs low enough for beacon use must be quite a challenge. At work, all of our DDS based signal generators, including the pricey ones, have quite a few spurs at the -80 dBc level- the nuisance is that they do not have easily predictable frequencies. We moan to the manufacturers but I have not seen much improvement over the last decade.

John, what sort of phase noise numbers do you get from the GB3MHZ beacon?

Regards,

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.
_____________________________________________________


Virus-free. www.avast.com


--
Robin Szemeti - G1YFG


Re: New MGM Modes on Beacons

John Quarmby
 

Alwyn

I have not got hard numbers to hand, but I can compare it with the 23cm beacon, where the beacon is approximately 95dB above noise in 2.5kHz bandwidth and results in a rise in the apparent band noise of 5db when I beam at it on 1296.200. My LO and the beacon oscillator are almost identical, so probably each contributes the same amount of phase noise. I have a crystal notch filter in the 28MHz transverter IF to reduce the beacon signal level by about 50dB going into the K3.

The 13cm beacon is about 10dB weaker, there is no change in band noise at 2320.200 when I beam at it. There are no major spurs in the SSB/CW part of the band, but they are apparent in the beacon band. When we have got it on air again I will make some proper measurements.

73

John G3XDY

On 16/03/2021 13:19, alwyn.seeds1 wrote:
Dear John and Andy,

Getting DDS spurs low enough for beacon use must be quite a challenge. At work, all of our DDS based signal generators, including the pricey ones, have quite a few spurs at the -80 dBc level- the nuisance is that they do not have easily predictable frequencies. We moan to the manufacturers but I have not seen much improvement over the last decade.

John, what sort of phase noise numbers do you get from the GB3MHZ beacon?

Regards,

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.
_____________________________________________________


Virus-free. www.avast.com


Re: New MGM Modes on Beacons

alwyn.seeds1
 

Dear John and Andy,

Getting DDS spurs low enough for beacon use must be quite a challenge. At work, all of our DDS based signal generators, including the pricey ones, have quite a few spurs at the -80 dBc level- the nuisance is that they do not have easily predictable frequencies. We moan to the manufacturers but I have not seen much improvement over the last decade.

John, what sort of phase noise numbers do you get from the GB3MHZ beacon?

Regards,

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: New MGM Modes on Beacons

John Quarmby
 

Plenty of food for thought Andy, thank you very much. I'm thinking that upgrading existing beacons to retain low phase noise and spurs might be easiest by using a fixed RDDS for frequency control, with a baseband I/Q modulator driven from a PIC via DACs modulating the output of the RDDS to provide all the modes required.

The 13cm version of GB3MHZ (when it is working!) uses a Next Gen Beacon source running on 320.830MHz with FSK CW and PI4, mixed with 2GHz multiplied from the 1GHz Next Gen clock. Phase noise performance is quite respectable, and in band spurs are just about acceptable here 4km LoS from the beacon.

73

John G3XDY

On 16/03/2021 10:21, Andy G4JNT wrote:

[Edited Message Follows]
[Reason: A pile of silly typos corrected]

With the introduction of new modes within the WSJT-X suite that use Gaussian shift MFSK, the old technique of switching between several switched tones using either a DDS or Fract-N PLL is no longer valid
 
Although not yet really applicable to microwaves, where JT4, JT65/Qxxx and PI4 will continue to reign, it is worth thinking about ways to implement FST4 and FT8/4 ready for if and when new GFSK modes appear that are suited to uWave usage.
 
This paper summarises the situation to date, and suggests a few ways forward.
 
 
 
Andy
 

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