Date   
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

Re: Transmitter Linearity

Wolfgang Hoeth OE4WOG
 

fully agree to this statement, as the number of active Microwavers steadily increase, we must pay more attention to the signal purity of LO`s and PA`s on our microwave gear.
 
73, Wolfgang, OE4WOG
 
------ Originalnachricht ------
Von: "'dominique.dehays' Dominique.DEHAYS@... [ukmicrowaves]" <ukmicrowaves@...>
Gesendet: 07.09.2016 09:36:20
Betreff: Re: [ukmicrowaves] Transmitter Linearity
 
Hi agn ,

yes , I think it's never a good idea to say : let's go dirty , it would'nt hurt anyone. The exemple I took with RS can be extended to tropo as well. The activity level on 3cm requires we stay clean

73
Dom

    Le 07/09/2016 09:19, 'Chris Bartram' cbartram@... [ukmicrowaves] a écrit :
               

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 ,

yes , I think it's never a good idea to say : let's go dirty , it would'nt hurt anyone. The exemple I took with RS can be extended to tropo as well. The activity level on 3cm requires we stay clean

73
Dom

Le 07/09/2016 09:19, 'Chris Bartram' cbartram@... [ukmicrowaves] a écrit :
 

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




Transmitter Linearity

Chris Bartram <cbartram@...>
 

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: The full email - TGA2760

SAM JEWELL
 

Of course when RS signals are that strong who can tell what the SSB sounds like anyway? Time to go CW.......narrower. Or go FM?
😊
73 de Sam, G4DDK



On 6 Sep 2016, at 12:45, 'dominique.dehays' Dominique.DEHAYS@... [ukmicrowaves] <ukmicrowaves@...> wrote:

 

Hi ,

looks like we don't live in the same galaxy, I can tell U we care ,
during a RS opening there are something like 10 stations on the band and
some with absolutely outstanding levels
During a good event signals from Paris and Beauvais , close to 700km
away are 9++++++++ , this is then we decide to try 24Ghz RS

73
Dom

Re: The full email - TGA2760

F6DRO
 

Hi ,

looks like we don't live in the same galaxy, I can tell U we care , during a RS opening there are something like 10 stations on the band and some with absolutely outstanding levels
During a good event signals from Paris and Beauvais , close to 700km away are 9++++++++ , this is then we decide to try 24Ghz RS

73
Dom

Re: The full email - TGA2760

Andy G4JNT
 

And do we really care about the sidebands on an SSB signal on 10GHz?   Even in the biggest events from a hilltop site , you're unlikely to hear more than two stations simultaneously.

Back in the 1990's when many of us ran TWTs, running them well into compression was common, and no one complained.

'jnt


On 6 September 2016 at 11:49, 'dominique.dehays' Dominique.DEHAYS@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

Hi all ,

what about constant amplitude ssb? It was promoted a long time ago , and
was sadt to be very interesting too for high bands microwaves at it was
possible to use a varactor multiplier with a SSB tx.
I recall in the 70's the late F1ANH using this modulation mode to avoid
detection of the surroundings neighbours TVs

73
Dom


Re: The full email - TGA2760

F6DRO
 

Hi all ,

what about constant amplitude ssb? It was promoted a long time ago , and was sadt to be very interesting too for high bands microwaves at it was possible to use a varactor multiplier with a SSB tx.
I recall in the 70's the late F1ANH using this modulation mode to avoid detection of the surroundings neighbours TVs

73
Dom

Re: The full email - TGA2760

Chris Bartram <cbartram@...>
 

 Hello Neil

There is a third alternative to linearising PAs. It's quite possible to use an analogue lineariser to compensate for PA non-linearities. It doesn't work as well as adaptive linearisation, as the transfer characteristics of the PA, both in amplitude and phase,  won't be static with time and temperature, but for typical amateur SSB operation it would probably be good enough! One thought is that for SSB, this could be done at audio. Incidentally, predistortion does not involve a conventional negative feedback mechanism, (The term 'adaptive feedback' which I seen in amateur literature is very misleading. Feedback linearisation of amplifiers is a very different process.) as there is far too much latency in the necessary processing. Rather the predistortion operates to adjust the signal path outside the modulation bandwidth.

I can't imagine that manufacturers like ELAD aren't working on predistortion schemes. It's not a trivial task, but the improvement in performance which can be obtained is spectacular. Despite some opposition, I encouraged the maker of some PAs I designed a few years ago for the amateur VHF bands to incorporate a sampling port for adaptive feedback, and the results have been very good. Don't forget though, that you need to incorporate an extremely linear downconverter sharing a common transverter LO to make good use of adaptive linearisation.

Vy 73

Chris
GW4DGU/A

GB3USK off again

Graham G3TCT
 

Sorry to report the beacon is off air at the moment while the batteries get recharged. We need some serious sunshine and/or wind! Will advise further.

Graham

Re: The full email - TGA2760

Neil Smith G4DBN
 

I am thinking in terms of milling a 5mm deep bathtub in a slab of copper, then using one of the small CNC mills to machine a simple PCB shape (have to embed it on a wax base or something), with a hole in the middle and exponential curves either side of the input and output where you would normally use vast numbers of PTHs, then milling the inverse of the board into the copper.  Fit the SMD passives using normal high-temp solder, then drop the pieces of board into the depressions with a bit of low melting point solder beneath, clamp it  together with some spring fingers to hold the bits of board in place, and pop the chip in place with low-temp solder paste underneath and on the contact points on the board.  Slap the whole thing on a hotplate and cross fingers tightly.

Pop a machined copper cap over the thing, perhaps with some sorbo foam.  Watercool it, or use a decent Peltier cooler or perhaps a heatpipe and fans and it might just work.  Definitely not mass-production, but certainly ham radio.

I've asked the manufacturer of my SDR (Elad) if it is possible to do adaptive predistortion, or if not, a static predistortion map on the TX that is the inverse of the compression curve.

My 3D-printing-nerd chum says he would just print the wanted copper shape in PLA, make an investment cast, burn off the PLA in a kiln, melt some free-flowing bronze and pour it into the investment cast and avoid all that nasty machining.  3D print is his answer to *everything* though.

Might be a whole lot easier just to shell out for one of the more linear GaN MMICs like the one Charlie published in DUBUS, but the pricing is somewhat breathtaking.

Neil G4DBN


On 05/09/2016 18:19, 'Chris Bartram' cbartram@... [ukmicrowaves] wrote:
 

(This email became truncated when sent via my webmail server. Better luck this time, I hope!)

A couple of points regarding GaN devices and SM mounting of small power parts.

Firstly, the saturation characteristic of the generation of devices including the TGA2760 is such that they do not suddenly go into heavy compression beyond P(1dB). Rather, they have useful gain to beyond 3dB compression. This is not a problem for constant amplitude modulation schemes, but of course, isn't really suitable for SSB or COFDM without further processing.

As radio amateurs are the only people who use SSB to any extent above 30MHz, we don't count in the device manufacturer's great scheme of things! Professional, and other users of COFDM eg.DATV, will nowadays be designing and using transmitters which employ adaptive linearisation, so they don't need to worry too much about the additional non-linearity of the PA device on signal peaks: they are generally chasing the better efficiency, and the broadband characteristics (stemming from the intrinsically higher impedances) of the GaN device. Of course, there are amateur exciters which feature adaptive linearisation available, such as the  Hermes derived SDRs, including the
Heatsinking SMD packages has to done very well if reliability isn't to be compromised. A problem is that the number of holes required will probably put manufacture beyond low-cost PCB suppliers. Additionally, the material required to make a good board for high-power RF at is unlikely to be an off-the-shelf item, and that will reduce the number of cheapy suppliers to a number approaching zero! If it's possible to eliminate the multiple-via pad - and Neil's suggestion is entirely sound - and also to remove any need for plated-through holes, this would much simplify the manufacture of a board - reducing it to something which could (could just about!) be done at home.

PCB materials have improved a lot in the last few years, and there is now a generation of low-loss, generally thermoset, substrates such as Rogers 4720 (I think that's the right number) which have both good low-loss performance and excellent thermal conductivity. The days of Duroid and its ilk are long past!

Vy 73

Chris
GW4DGU/A



Virus-free. www.avast.com

The full email - TGA2760

Chris Bartram <cbartram@...>
 

(This email became truncated when sent via my webmail server. Better luck this time, I hope!)

A couple of points regarding GaN devices and SM mounting of small power parts.

Firstly, the saturation characteristic of the generation of devices including the TGA2760 is such that they do not suddenly go into heavy compression beyond P(1dB). Rather, they have useful gain to beyond 3dB compression. This is not a problem for constant amplitude modulation schemes, but of course, isn't really suitable for SSB or COFDM without further processing.

As radio amateurs are the only people who use SSB to any extent above 30MHz, we don't count in the device manufacturer's great scheme of things! Professional, and other users of COFDM eg.DATV, will nowadays be designing and using transmitters which employ adaptive linearisation, so they don't need to worry too much about the additional non-linearity of the PA device on signal peaks: they are generally chasing the better efficiency, and the broadband characteristics (stemming from the intrinsically higher impedances) of the GaN device. Of course, there are amateur exciters which feature adaptive linearisation available, such as the  Hermes derived SDRs, including the
Heatsinking SMD packages has to done very well if reliability isn't to be compromised. A problem is that the number of holes required will probably put manufacture beyond low-cost PCB suppliers. Additionally, the material required to make a good board for high-power RF at is unlikely to be an off-the-shelf item, and that will reduce the number of cheapy suppliers to a number approaching zero! If it's possible to eliminate the multiple-via pad - and Neil's suggestion is entirely sound - and also to remove any need for plated-through holes, this would much simplify the manufacture of a board - reducing it to something which could (could just about!) be done at home.

PCB materials have improved a lot in the last few years, and there is now a generation of low-loss, generally thermoset, substrates such as Rogers 4720 (I think that's the right number) which have both good low-loss performance and excellent thermal conductivity. The days of Duroid and its ilk are long past!

Vy 73

Chris
GW4DGU/A

QRV 9cm again

g4bao
 

Hi all,
I'm QRV on 9cm again from JO02cg if anyone would like to try a QSO?

Copying GB3MHZ, GB3OHM, GB3SCX and occasionally G3LPC beacons

Running about 15Watts at a dual dipole feed, offset slightly from the 10/24GHz feed in my 60cm offset dish at 8m agl.
 
Homebrew,  Ionica-based transverter plus a G4DDK VLNA9 masthead preamp

RX system Noise figure approx 1.2dB

Email me or Tweet @g4bao if you want a sked.

Tropo, Aircraft scatter, SSB, CW, JT modes? 

73
John

   

Re: TGA2760-SM

Chris Bartram <cbartram@...>
 

 
A couple of points regarding GaN devices and SM mounting of small power parts.

Firstly, the saturation characteristic of the generation of devices including the TGA2760 is such that they do not suddenly go into heavy compression beyond P(1dB). Rather, they have useful gain to beyond 3dB compression. This is not a problem for constant amplitude modulation schemes, but of course, isn't really suitable for SSB or COFDM without further processing.

As radio amateurs are the only people who use SSB to any extent above 30MHz, we don't count in the device manufacturer's great scheme of things! Professional, and other users of COFDM eg.DATV, will nowadays be using transmitters which employ adaptive linearisation, so they don't need to worry too much about the additional non-linearity of the PA device on signal peaks: they are generally chasing the better efficiency, and broadband characteristics (stemming from the intrinsically higher impedances) of the GaN device. Of course, there are amateur exciters which feature adaptive linearisation available, such as the  Hermes derived SDRs, including the
Heatsinking SMD packages has to done very well if reliability isn't to be compromised. A problem is that the number of holes required will probably put manufacture beyond low-cost PCB suppliers. Additionally, the material required to make a good board for high-power RF at is unlikely to be an off-the-shelf item, and that will reduce the number of cheapy suppliers to a number approaching zero! If it's possible to eliminate the multiple-via pad - and Neil's suggestion is entirely sound - and also to remove any need for plated-through holes, this would much simplify the manufacture of a board - reducing it to something which could (could just about!) be done at home.

PCB materials have improved a lot in the last few years, and there is now a generation of low-loss, generally thermoset, substrates such as Rogers 4720 (I think that's the right number) which have both good low-loss performance and excellent thermal conductivity. The days of Duroid and its ilk are long past!

Vy 73

Chris
GW4DGU/A

Re: TGA2760-SM

Andy G4JNT
 

If you think these PAs have potential for the masses, it may be worth getting a PCB made to order and passing on teh rest to other people at cost.  There are a number of low cost suppliers out there now, and getting perhaps 10 or 15 made can be quite cost effective these days.

That way you can have all the plated though holes you want and do the PCB the way the manufacturer recommends.  Its really not worth faffing about trying to do it on the cheap with a chip costing £80 or so.

I haven't used any of those Chinese / Bulgarian / whatever cheap suppliers though. Only ever Number One Systems in Newbury.  But even they become quite cost-effective for 25 off or more.

'jnt


On 4 September 2016 at 21:47, Neil neil@... [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

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@yahoogroups.com
> [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@yahoogroups.com?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]
>
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Re: TGA2760-SM

Neil Smith G4DBN
 

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

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Re: TGA2760-SM

Andy G4JNT
 

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 you're 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@... [ukmicrowaves] <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 $600-$900 GaN PA MMICs.

Perhaps the answer is to get a couple and play with them and see what
happens.

Neil G4DBN