Date   

ukmicrowaves contest

Peter G3SMT
 

Will anyone be operating this weekend from the Shropshire / Powys area?

I have a friend staying with me from the San Diego Microwave Group and it would be good to show him some of our stations / equipment. He will enjoy the rain and wind as they don't get much in SD !!

73

Peter

G3SMT


calling / working frequency

Paul G8KFW
 

Hi all could someone please help with the calling / working frequency that are currently being used and if there is any intention to change them

The bands of interest are    24 , 47 , 76 , 135  Ghz 

Regards Paul B



Re: TGA2760-SM

Neil Smith G4DBN
 

In a private email an amateur who is also makes jewellery suggests using silver alloy as the heat spreader, using the Delft Clay technique and casting using scrap silver. Alternatively it might be a even simpler to machine the heat spreader and PCB mount using silver instead of copper. A new 3mm thick Sterling silver plate 30 x 40 mm costs around £30. Probably save that in broken milling cutters,compared with using copper….
Neil G4DBN


Re: TGA2760-SM

Neil Smith G4DBN
 

Thanks Eric, I did consider using a round slug for a prototype, drilling a round hole under the chip right through the copper base and pcb, so I could press it into place and get more contact area. I think I need to talk to my friend who has a tiny CNC mill to see how easy it will be to machine the pcb and copper base. I may need to use a Peltier cooler to avoid large temperature excursions to prevent differential expansion issues.
Certainly considering multiple parallel devices, perhaps with waveguide combiners rather than hybrids.
Neil G4DBN

On 8 Sep 2016, at 23:48, Eric Haskell eric_haskell@... [ukmicrowaves] <ukmicrowaves@...> wrote:


>{I'm trying to work out if I can machine out a hollow in solid copper 
but leave a rectangular post in the centre the thickness of the PCB, 
then cut a rectangular hole in the centre of the PCB, fit the PCB over 
the post, and solder the PCB to the copper and the device to the PCB and 
copper post using 138C bismuth-tin like I did for the 23cm PAs. Might 
be a lot simpler than getting a PCB made with hundreds of teensy pths.  
Wouldn't work for mass production, but maybe feasible for a one-off.  
This hobby gets more like jewellery-making by the minute...
Neil G4DBN}

Neil,  I wounder it it might be easier to cut a rectangular copper slug the size of the ground on the bottom of the part and same thickness as PCB.  Have a PCB made with a rectangular hole. Solder all the other parts to the PCB.  Insert the slug into the rectangular hole in the PCB.   Lay PCB and slug on a pre-tined copper heatsink siting on a hotplate and reflow together.  Then apply solder or solder paste to device area of PCB and reflow device onto PCB. Add edge mount SMA connectors and solder on a sheild.  We may need to take some the the thermal CTE is matched fairly close between copper slug and PCB substrate material so that thermal expansion does not pull everything apart.  Also thinking about paralleling 2 parts with Wilkinsons for more power. Seems like a good fit for constant envelope modulation modes or CW with the high saturated power output.

Eric Haskell,
KC4YOE





To: ukmicrowaves@...
From: ukmicrowaves@...
Date: Sun, 4 Sep 2016 21:47:11 +0100
Subject: Re: [ukmicrowaves] TGA2760-SM

 
I'm trying to work out if I can machine out a hollow in solid copper 
but leave a rectangular post in the centre the thickness of the PCB, 
then cut a rectangular hole in the centre of the PCB, fit the PCB over 
the post, and solder the PCB to the copper and the device to the PCB and 
copper post using 138C bismuth-tin like I did for the 23cm PAs. Might 
be a lot simpler than getting a PCB made with hundreds of teensy pths.  
Wouldn't work for mass production, but maybe feasible for a one-off.  
This hobby gets more like jewellery-making by the minute...
Neil G4DBN

On Sun, 4 Sep 2016 20:52:12 +0100, Andy Talbot andy.g4jnt@... 
[ukmicrowaves] wrote:
> Make sure you use the proper PCB layout then - I was looking at the
> data sheet for it and see the cooling needs ot be  via hundreds of
> plated though holes to the lower ground plane face of the PCB and
> thence to the heatsink.   So getting rid of tens of watts of heat
> needs proper attention to PCB detail.  
>
> But youre right - it does seem very cheap for that sort of Psat.   
> ... and only needing a few milliwatts of drive too...
>
> jnt
>
> On 4 September 2016 at 20:45, Neil neil@... [1] [ukmicrowaves]
> wrote:
>
>>  
>>
>> The device looks like a three-stage MMIC, running with the finals
>> at
>> 28V, but it still seems weird that the P1dB is only 2 watts or so
>> when
>> Psat is about 15 watts. For the price, it looks like a brilliant
>> deal
>> to get serious power on CW/JT modes on 3cm, but would it be
>> feasible to
>> use predistortion on an SDR IF rig in SSB mode to get a fairly
>> linear
>> response at high power, despite what looks like unspeakable
>> nonlinearity? After all, a pair of these 60 quid devices gives as
>> much
>> power as some of the 0-0 GaN PA MMICs.
>>
>> Perhaps the answer is to get a couple and play with them and see
>> what
>> happens.
>>
>> Neil G4DBN
>
> 
>
> Links:
> ------
> [1] mailto:neil@...
> [2] mailto:ukmicrowaves@...
> [3]
> 
> https://groups.yahoo.com/neo/groups/ukmicrowaves/conversations/messages/40258;_ylc=X3oDMTJxamY2aGk0BF9TAzk3MzU5NzE0BGdycElkAzgwOTAxMjEEZ3Jwc3BJZAMxNzA1MDYzMTA4BG1zZ0lkAzQwMjU4BHNlYwNmdHIEc2xrA3JwbHkEc3RpbWUDMTQ3MzAxODczNQ--?act=reply&messageNum=40258
> [4]
> 
> mailto:andy.g4jnt@...?subject=Re%3A%20%5Bukmicrowaves%5D%20TGA2760-SM
> [5]
> 
> mailto:ukmicrowaves@...?subject=Re%3A%20%5Bukmicrowaves%5D%20TGA2760-SM
> [6]
> 
> https://groups.yahoo.com/neo/groups/ukmicrowaves/conversations/newtopic;_ylc=X3oDMTJlbXRjcWU0BF9TAzk3MzU5NzE0BGdycElkAzgwOTAxMjEEZ3Jwc3BJZAMxNzA1MDYzMTA4BHNlYwNmdHIEc2xrA250cGMEc3RpbWUDMTQ3MzAxODczNQ--
> [7]
> 
> https://groups.yahoo.com/neo/groups/ukmicrowaves/conversations/topics/40248;_ylc=X3oDMTM2bnJyZGo2BF9TAzk3MzU5NzE0BGdycElkAzgwOTAxMjEEZ3Jwc3BJZAMxNzA1MDYzMTA4BG1zZ0lkAzQwMjU4BHNlYwNmdHIEc2xrA3Z0cGMEc3RpbWUDMTQ3MzAxODczNQR0cGNJZAM0MDI0OA--
> [8] https://yho.com/1wwmgg
> [9]
> 
> https://groups.yahoo.com/neo/groups/ukmicrowaves/info;_ylc=X3oDMTJldm5hdjNkBF9TAzk3MzU5NzE0BGdycElkAzgwOTAxMjEEZ3Jwc3BJZAMxNzA1MDYzMTA4BHNlYwN2dGwEc2xrA3ZnaHAEc3RpbWUDMTQ3MzAxODczNQ--
> [10]
> 
> https://groups.yahoo.com/neo;_ylc=X3oDMTJkNjQyZXU2BF9TAzk3NDc2NTkwBGdycElkAzgwOTAxMjEEZ3Jwc3BJZAMxNzA1MDYzMTA4BHNlYwNmdHIEc2xrA2dmcARzdGltZQMxNDczMDE4NzM1
> [11] https://info.yahoo.com/privacy/us/yahoo/groups/details.html
> [12] 
> mailto:ukmicrowaves-unsubscribe@...?subject=Unsubscribe
> [13] https://info.yahoo.com/legal/us/yahoo/utos/terms/





Re: TGA2760-SM

Eric Haskell <eric_haskell@...>
 

>{I'm trying to work out if I can machine out a hollow in solid copper
but leave a rectangular post in the centre the thickness of the PCB,
then cut a rectangular hole in the centre of the PCB, fit the PCB over
the post, and solder the PCB to the copper and the device to the PCB and
copper post using 138C bismuth-tin like I did for the 23cm PAs. Might
be a lot simpler than getting a PCB made with hundreds of teensy pths.
Wouldn't work for mass production, but maybe feasible for a one-off.
This hobby gets more like jewellery-making by the minute...
Neil G4DBN}

Neil,  I wounder it it might be easier to cut a rectangular copper slug the size of the ground on the bottom of the part and same thickness as PCB.  Have a PCB made with a rectangular hole. Solder all the other parts to the PCB.  Insert the slug into the rectangular hole in the PCB.   Lay PCB and slug on a pre-tined copper heatsink siting on a hotplate and reflow together.  Then apply solder or solder paste to device area of PCB and reflow device onto PCB. Add edge mount SMA connectors and solder on a sheild.  We may need to take some the the thermal CTE is matched fairly close between copper slug and PCB substrate material so that thermal expansion does not pull everything apart.  Also thinking about paralleling 2 parts with Wilkinsons for more power. Seems like a good fit for constant envelope modulation modes or CW with the high saturated power output.

Eric Haskell,
KC4YOE





To: ukmicrowaves@...
From: ukmicrowaves@...
Date: Sun, 4 Sep 2016 21:47:11 +0100
Subject: Re: [ukmicrowaves] TGA2760-SM

 
I'm trying to work out if I can machine out a hollow in solid copper
but leave a rectangular post in the centre the thickness of the PCB,
then cut a rectangular hole in the centre of the PCB, fit the PCB over
the post, and solder the PCB to the copper and the device to the PCB and
copper post using 138C bismuth-tin like I did for the 23cm PAs. Might
be a lot simpler than getting a PCB made with hundreds of teensy pths.
Wouldn't work for mass production, but maybe feasible for a one-off.
This hobby gets more like jewellery-making by the minute...
Neil G4DBN

On Sun, 4 Sep 2016 20:52:12 +0100, Andy Talbot andy.g4jnt@...
[ukmicrowaves] wrote:
> Make sure you use the proper PCB layout then - I was looking at the
> data sheet for it and see the cooling needs ot be  via hundreds of
> plated though holes to the lower ground plane face of the PCB and
> thence to the heatsink.   So getting rid of tens of watts of heat
> needs proper attention to PCB detail.  
>
> But youre right - it does seem very cheap for that sort of Psat.   
> ... and only needing a few milliwatts of drive too...
>
> jnt
>
> On 4 September 2016 at 20:45, Neil neil@... [1] [ukmicrowaves]
> wrote:
>
>>  
>>
>> The device looks like a three-stage MMIC, running with the finals
>> at
>> 28V, but it still seems weird that the P1dB is only 2 watts or so
>> when
>> Psat is about 15 watts. For the price, it looks like a brilliant
>> deal
>> to get serious power on CW/JT modes on 3cm, but would it be
>> feasible to
>> use predistortion on an SDR IF rig in SSB mode to get a fairly
>> linear
>> response at high power, despite what looks like unspeakable
>> nonlinearity? After all, a pair of these 60 quid devices gives as
>> much
>> power as some of the 0-0 GaN PA MMICs.
>>
>> Perhaps the answer is to get a couple and play with them and see
>> what
>> happens.
>>
>> Neil G4DBN
>
>
>
> Links:
> ------
> [1] mailto:neil@...
> [2] mailto:ukmicrowaves@...
> [3]
>
> https://groups.yahoo.com/neo/groups/ukmicrowaves/conversations/messages/40258;_ylc=X3oDMTJxamY2aGk0BF9TAzk3MzU5NzE0BGdycElkAzgwOTAxMjEEZ3Jwc3BJZAMxNzA1MDYzMTA4BG1zZ0lkAzQwMjU4BHNlYwNmdHIEc2xrA3JwbHkEc3RpbWUDMTQ3MzAxODczNQ--?act=reply&messageNum=40258
> [4]
>
> mailto:andy.g4jnt@...?subject=Re%3A%20%5Bukmicrowaves%5D%20TGA2760-SM
> [5]
>
> mailto:ukmicrowaves@...?subject=Re%3A%20%5Bukmicrowaves%5D%20TGA2760-SM
> [6]
>
> https://groups.yahoo.com/neo/groups/ukmicrowaves/conversations/newtopic;_ylc=X3oDMTJlbXRjcWU0BF9TAzk3MzU5NzE0BGdycElkAzgwOTAxMjEEZ3Jwc3BJZAMxNzA1MDYzMTA4BHNlYwNmdHIEc2xrA250cGMEc3RpbWUDMTQ3MzAxODczNQ--
> [7]
>
> https://groups.yahoo.com/neo/groups/ukmicrowaves/conversations/topics/40248;_ylc=X3oDMTM2bnJyZGo2BF9TAzk3MzU5NzE0BGdycElkAzgwOTAxMjEEZ3Jwc3BJZAMxNzA1MDYzMTA4BG1zZ0lkAzQwMjU4BHNlYwNmdHIEc2xrA3Z0cGMEc3RpbWUDMTQ3MzAxODczNQR0cGNJZAM0MDI0OA--
> [8] https://yho.com/1wwmgg
> [9]
>
> https://groups.yahoo.com/neo/groups/ukmicrowaves/info;_ylc=X3oDMTJldm5hdjNkBF9TAzk3MzU5NzE0BGdycElkAzgwOTAxMjEEZ3Jwc3BJZAMxNzA1MDYzMTA4BHNlYwN2dGwEc2xrA3ZnaHAEc3RpbWUDMTQ3MzAxODczNQ--
> [10]
>
> https://groups.yahoo.com/neo;_ylc=X3oDMTJkNjQyZXU2BF9TAzk3NDc2NTkwBGdycElkAzgwOTAxMjEEZ3Jwc3BJZAMxNzA1MDYzMTA4BHNlYwNmdHIEc2xrA2dmcARzdGltZQMxNDczMDE4NzM1
> [11] https://info.yahoo.com/privacy/us/yahoo/groups/details.html
> [12]
> mailto:ukmicrowaves-unsubscribe@...?subject=Unsubscribe
> [13] https://info.yahoo.com/legal/us/yahoo/utos/terms/



GB3USK status

Graham G3TCT
 

We have made some changes to the power system which will hopefully make GB3USK a more reliable service. However, we need to let the batteries recover their charge as they got rather depleted recently. So the beacon is off air at the moment, and I hope to get it back on next week. Don't pull your rig apart if you can't hear it in the meantime!

73
Graham


Re: MSF

Andy G4JNT
 

Nowadays, as nearly all MSF clocks only update at midnight, 0100, 0200 and 0300, the keepers of Anthorn no-doubt take this into account when doing maintenance,  turning it back on during the night.   

Since most of the maintenance will involve cleaning insulators with the signal off for safety reasons, there's no reason why it shouldn't go back on at night resulting in  no inconvenience for perhaps 99% of the users.

'JNT



On 8 September 2016 at 15:35, 'Michael Scott' g3lyp@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

Thanks Andy, I have an Oregon Scientific clock which has a bargraph indicator of the signal strength and it has shown no change in signal strength nor has the watch which has  a dish shaped icon which falls to bits if the signal is weak. I wonder if these may be taking a signal from a European transmitter rather than Anthorn. I also have a Junghans clock, but it seems to be low on sensitivity, and frequently doesn’t see any signal for several hours!
 
Thanks also Martin, I didn’t realise SUWS covered that low in frequency.
 
Mike
 
Sent: Thursday, September 8, 2016 12:59 PM
Subject: Re: [ukmicrowaves] MSF
 
 

It's on at the moment:  my super antiquated Junghams Mega says so and it looks for a signal every hour.   All modern MSF clocks only lock up once or twice in the middle of the night they so wouldn't  "know" about, or show, any daytime outages.
 
'JNT

 
On 8 September 2016 at 12:49, 'Michael Scott' g3lyp@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 
Hi All
 
Does anyone know if the MSF 60kHz signal is actually off the air? It was scheduled to be off between 1000 – 1400 today, but both my RC clock and watch show the presence of a signal.
 
73, Mike, G3LYP
 



Re: MSF

Michael Scott
 

Thanks Andy, I have an Oregon Scientific clock which has a bargraph indicator of the signal strength and it has shown no change in signal strength nor has the watch which has  a dish shaped icon which falls to bits if the signal is weak. I wonder if these may be taking a signal from a European transmitter rather than Anthorn. I also have a Junghans clock, but it seems to be low on sensitivity, and frequently doesn’t see any signal for several hours!
 
Thanks also Martin, I didn’t realise SUWS covered that low in frequency.
 
Mike
 

Sent: Thursday, September 8, 2016 12:59 PM
Subject: Re: [ukmicrowaves] MSF
 
 

It's on at the moment:  my super antiquated Junghams Mega says so and it looks for a signal every hour.   All modern MSF clocks only lock up once or twice in the middle of the night they so wouldn't  "know" about, or show, any daytime outages.
 
'JNT

 
On 8 September 2016 at 12:49, 'Michael Scott' g3lyp@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 
Hi All
 
Does anyone know if the MSF 60kHz signal is actually off the air? It was scheduled to be off between 1000 – 1400 today, but both my RC clock and watch show the presence of a signal.
 
73, Mike, G3LYP
 


Re: MSF

Martin - G8JNJ
 

Hi,

It's on - you can check anytime via the SUWS WEB SDR.


Regards,

Martin - G8JNJ

www.g8jnj.net
www.tc2m.info

 




Re: MSF

Andy G4JNT
 

It's on at the moment:  my super antiquated Junghams Mega says so and it looks for a signal every hour.   All modern MSF clocks only lock up once or twice in the middle of the night they so wouldn't  "know" about, or show, any daytime outages.

'JNT


On 8 September 2016 at 12:49, 'Michael Scott' g3lyp@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

Hi All
 
Does anyone know if the MSF 60kHz signal is actually off the air? It was scheduled to be off between 1000 – 1400 today, but both my RC clock and watch show the presence of a signal.
 
73, Mike, G3LYP



MSF

Michael Scott
 

Hi All
 
Does anyone know if the MSF 60kHz signal is actually off the air? It was scheduled to be off between 1000 – 1400 today, but both my RC clock and watch show the presence of a signal.
 
73, Mike, G3LYP


Re: Activity List for UK Microwave Group 24/47/76GHz Contest - Sunday 11th September

g4bao
 

It looks like everyone's too far West again but I can be available for tests from home on 24GHz on request. I'm QTHR and in the phone book so call me on the landline, via twitter @g4bao, email or find me on KST if you want a test.

I might even be tempted to take my 24GHz /P system to Therfield IO92xa if anyone's in range and it's a nice day!  

Callsign: G4BAO
Locator: JO02cg33
Band: 24GHz 1W 60CM Dish @8m AGL



On 7 September 2016 at 23:23, Keith Winnard gw3tkh@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

Callsigns: GW3TKH/P & GW4HQX/P
Locator: IO81LS19 Cefn Y Galchen
Bands: ('TKH) 24GHz 0.5W 45cm dish, 47GHz 50mW 30cm dish,
76GHz ?uW 34dBi lens horn + G8CUB beacon tx.
Bands: ('HQX) 47GHz 100uW 30cm dish,
76GHz ?uW 34dBi lens horn + G8CUB beacon tx.
Talkback: 144.175,  mob: 07762 885015
Times: 10.00 BST onwards

Keith
GW3TKH



From: "g8cub@... [ukmicrowaves]" <ukmicrowaves@...>
To: ukmicrowaves@...
Sent: Wednesday, 7 September 2016, 14:04
Subject: [ukmicrowaves] Activity List for UK Microwave Group 24/47/76GHz Contest - Sunday 11th September

 
With the last of the millimetre cumulatives contests this weekend. It has fallen on me to compile a list htis time.

 Please send details of your planned
operation in the following format:

Callsign: G8CUB/P
Locator: IO81WU70 Birdlip, IO91CL12 Hackpen
Bands: 24GHz 1W 20dB horn, 47GHz 30mW 30cm dish,
76GHz 50mW 150mm horn / 60cm dish

Talkback: 144.175, KST maybe, mob: 07900 261121
Times: Birdlip ~ 10.00 -12.00, Hackpen ~13.00-15.00 BST

The weather prediction looks hopeful at the moment, so looking forward to working you.


Roger
G8CUB




Re: GB3SEE

Martin - G8JNJ
 

GB3SEE does seem to be off-air

Regards,

Martin - G8JNJ

www.g8jnj.net
www.tc2m.info
http://websdr.suws.org.uk



Re: GB3SEE

g3thq <g3thq@...>
 

Yes, went off yesterday and still off this morning (8 Sep 16).  Heat related?

73 Brian
NW London

--

On 07/09/2016 22:29, g4uvz@... [ukmicrowaves] wrote:
Is SEE off again ?



Re: Activity List for UK Microwave Group 24/47/76GHz Contest - Sunday 11th September

Keith GW3TKH
 

Callsigns: GW3TKH/P & GW4HQX/P
Locator: IO81LS19 Cefn Y Galchen
Bands: ('TKH) 24GHz 0.5W 45cm dish, 47GHz 50mW 30cm dish,
76GHz ?uW 34dBi lens horn + G8CUB beacon tx.
Bands: ('HQX) 47GHz 100uW 30cm dish,
76GHz ?uW 34dBi lens horn + G8CUB beacon tx.
Talkback: 144.175,  mob: 07762 885015
Times: 10.00 BST onwards

Keith
GW3TKH



From: "g8cub@... [ukmicrowaves]"
To: ukmicrowaves@...
Sent: Wednesday, 7 September 2016, 14:04
Subject: [ukmicrowaves] Activity List for UK Microwave Group 24/47/76GHz Contest - Sunday 11th September

 
With the last of the millimetre cumulatives contests this weekend. It has fallen on me to compile a list htis time.

 Please send details of your planned
operation in the following format:

Callsign: G8CUB/P
Locator: IO81WU70 Birdlip, IO91CL12 Hackpen
Bands: 24GHz 1W 20dB horn, 47GHz 30mW 30cm dish,
76GHz 50mW 150mm horn / 60cm dish

Talkback: 144.175, KST maybe, mob: 07900 261121
Times: Birdlip ~ 10.00 -12.00, Hackpen ~13.00-15.00 BST

The weather prediction looks hopeful at the moment, so looking forward to working you.


Roger
G8CUB



Re: GB3SEE

g4uvz@...
 

Is SEE off again ?


Second 5 GHz - 10 GHz satellite to launch

M5AKA
 

AMSAT-NA have already announced plans to launch a 5 GHz to 10 GHz amateur transponder payload into a Geosynchronous orbit https://amsat-uk.org/satellites/geosynchronous/na-gso-sat/

In addition they now plan to launch a 5 GHz to 10 GHz transponder satellite Heimdallr into Lunar orbit in September 2018.



Trevor M5AKA
----
AMSAT-UK http://amsat-uk.org/
Twitter https://twitter.com/AmsatUK
Facebook https://facebook.com/AmsatUK
YouTube https://youtube.com/AmsatUK
----



Activity List for UK Microwave Group 24/47/76GHz Contest - Sunday 11th September

Roger Ray
 

With the last of the millimetre cumulatives contests this weekend. It has fallen on me to compile a list htis time.


 Please send details of your planned
operation in the following format:

Callsign: G8CUB/P
Locator: IO81WU70 Birdlip, IO91CL12 Hackpen
Bands: 24GHz 1W 20dB horn, 47GHz 30mW 30cm dish,

76GHz 50mW 150mm horn / 60cm dish

Talkback: 144.175, KST maybe, mob: 07900 261121
Times: Birdlip ~ 10.00 -12.00, Hackpen ~13.00-15.00 BST


The weather prediction looks hopeful at the moment, so looking forward to working you.



Roger

G8CUB


Re: Transmitter Linearity

Andy G4JNT
 

I would argue that COFDM is not a way to improve weak signal performance.  COFDM and all the related modulations have as a prime aim to optimise bandwidth usage in defined channels and make the best use of allocated spectrum.    In data communications terms, they are generally referred to as "bandwidth-limited" modulation, making use of high order constellations like QAM and parallel stacked carriers themselves carrying QAM carrying .   They are NOT weak signal modes in their own right.  the need to conserve bandwidth automatically stops them having the best weak signal performance.

The reason for the overwhelming popularity of multicarrier OFDM modes is their resilience to multipath as the resulting symbol rate of teh multiple parallel tones is far lower than the combined data rate of the complete information stram.

In contrast, where bandwidth is not an issue but  power or S/N is, we enter the realm of "power limited" modulation. And this is where most of amateur radio sits.  But first of all you have to realise this does not just mean a wide signal bandwidth.   "Bandwidth expansion" means a lot more than this in signal processing terms.

Take as an example, repeating a messages (in SSB or Morse) five times to get it though.   It has taken 5 times as long to transmit the same amount of source information . In a way you could say it has been expanded 5 times. In data there are other ways of doing it.   You could expand the input data by adding error correction bits that increase it the same five-fold.  That would result in a far-stronger error correction (getting the message through) than the 5 times repeat can offer.

Back to modulation.   We rarely need more than a few tens of bits per second for normal QSO traffic.   Add very strong error correction which expands it say 5 times (and that is very strong indeed !) and you will get 100% copy at normalised S/N ratios (Eb/No) of  around 2 to 5dB depending on the actual modulation type - PSK, FSK.

But we are still only talking about a modulation that has to  carry say 1000 symbols per second.    And that will easily fit into  a 3kHz spectrum.   There's nothing to be gained in a pure additive noise environment by expanding further.   In fact there are  many purely practical advantages now of keeping modulation simple and using something  like basic FSK to overcome the practicalities of transmitters - like linearity.  

Even if the result is wider than it need be.   In spite of our reducing allocations, we still have a huge amount of spectrum to transmit a few hundred bits per second in.     3kHz arbitrary channelisation is still very wide in an AWGN environment.

Difficulties come when we consider extreme microwave paths including rain scatter and EME scintillation. And that requires a complete rethink  If we assume our signal is spread out to  a few hundred Hz, that automatically limits our symbol rate permitted to a fraction of that, say a few tens of symbols per second.  
We cannot POSSIBLY send anything with symbols moving faster or even approaching the random shifts of the spreading.  There's no hope of doing anything coherent

So we need to choose a modulation that can send that on a scattered path.   Its rather ironic, that the simplest modulation of its type, basic ON-OFF keying, is actually quite useful now.   We look for the power change over the entire tone-band of the spread signal and integrate down to the symbol speed   That way we look over a signal spreading bandwidth of say 200Hz but compress the result to say 10Hz.

Pure ON/OFF is wasteful of transmitter energy.  So we alternate between two tones, well separated in frequency to completely differentiate when the RS or scintillation or whatever, spreading occurs.  By comparing one tone's averaged power per symbol  against the other, 3dB advantage is gained over simple ON/OFF keying when transmitted peak power is compared [1]    [2]

By sending as one of, say,  64 tones instead of one of two, six information bits can be encoded at a time  so for paths that give only a few Hz of shift (VHF and down) multi FSK is used

To allow the symbol timing to be regenerated at the receiver, synchronisation signals have to be added to the symbols which reduces efficiency.   For really good weak signal performance and recovery this could be as much as another 100% overhead. 

But we're still only at 2k symbols per second for standard QSO speed .  For contest and routine Dx exchanges  with limited info content we can go a lot slower - which means less source information in the same bandwidth.  Or reduce the signal bandwidth further  by still heaver signal processing.    

The weak signal WSJT modes take all this into account and I think really do represent the best we are going to get on the amateur bands for weak signal Dx type working.    They don't support real time waffle type QSOs, where RTTY and PSK31 would be used, but for contest and EME exchanges and pre-formatted  messages can't be beaten

All the weak signal ones use  multi  FSK of 4,  9 or 65  tones with tone spacing options that can be chosen for the path. They all have a large overhead for synchronisation allowing for reliable lockup based only on a search in time and frequency over a limited range.

Up to recently that have all used similar error correction coding,   JT4, JT9 and WSPR all use convolutional coding with about three times expansion of the number of bits.   JT65 does it differently eiht Reed Solomon and its resulting six-symbol MFSK.      But they all have a similar performance in terms of normalised S/N (Eb/No)  needing about 4dB in their respective symbol bandwidths ranging from 1.5Hz for WSPR to 4.4Hz for JT4.  That puts it within about 4 dB (very roughly) of  Shannon's  theoretical limit for this modulation type.

The latest change is a completely new error correction coding in the latest version of WSJT, called QRA64.   The encoding is simpler than JT65, it is sent using the same modulation - one of 64 tones with a reduced synchronisation overhead  The clever bit comes in the decoding.   It is now believed to be within  0.6dB of the theoretical limit of Shannon limit for incoherent (FSK type ) modulation.



[1]  When you consider Tx MEAN power, two tone FSK and .OOK have identical performance.  The only difference being, you need a 200 Watt Tx, half on and half off, to equal a 100 Watt Tx sending FSK at 100% duty cycle.    Same mean, 3dB peak difference

[2] Coherent modes like PSK and QAM are inherently capable of better S/N performance than incoherent  FSK.  In fact, under ideal conditions  exactly 3dB better. Comparing two antipodal voltages for BPASK  instead of  power in two tone freqeuncies.   But coherency is complicated by the need for carrier recovery and phase locking, then symbol timing. The non linear processing needed for that, in a really weak signal situation with fading , multipath etc makes it a worse choice than keeping things simple and using non-coherent FSK.  Hence, why the all the WSJT modes for weak signal use use MFSK

Andy  G4JNT

On 7 September 2016 at 08:19, 'Chris Bartram' cbartram@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

FWIW, I accept that running an SSB transmitter well PA into compression isn't likely to cause the world to stop turning! However, I prefer to try to run my SSB transmitters linearly, rather than waste energy by spreading it across the band.

The real prize which comes from the use of more linear transmitters is the potential ability to use more effective modulation schemes than SSB, CW, or constant amplitude data. I have heard credible suggestions that the way to improve the weak signal performance of amateur radio (data) systems over real-world microwave paths is to use COFDM with wider bandwidths than the 2.3kHz occupied by SSB. This however requires a much more linear transmitter than most of us currently have. Practically that means the use of linearisation, and a software derived exciter.

Vy 73

Chris
GW4DGU/A





Re: Transmitter Linearity

F6DRO
 

Hi agn ,

the Constant amplitude ssb modulation system did not raised comments it looks:
http://www.ve6aqo.com/images/roel030406_beacon/PAoJTA%20PLL%20SSB.jpg

It can be done in software in a sdr transmitter , but I'm not sure , because I have not looked at it in detail ,that the statement this modulation can be with frequency multipliers is true.
If yes , it is a simple way to get some power on 47Ghz for exemple

732
Dom