GATs


Chris Bartram G4DGU
 

Hello Paul,

I did use a GAT3 and GAT5 at one time
I can't resist a comment on that ... So did I! I seem to remember using a GAT2 and GAT3 and maybe a GAT5. They taught me a lot about the need to get good T/R switching isolation, and to use proper sequencing for the c/o process :-)

My source was a certain Dr.(now Prof.) Cripps (ex-G3TPF) via Charlie, G3WDG. In about 1979 mine were used in a preamplifier for 432MHz EME, and very much from memory I achieved a noise figure of around 0.7dB measured by a thermal hot/cold source. that was more than 0.5dB better than I'd achieved with a then state of the art bipolar transistor. With my then 8 yagi antenna and about 700W from a K2RIW amplifier I could hear my own echoes most of the time. I also worked most of the stations then active on the band on CW, although Faraday wouldn't cooperate for a few. I think I was the first UK station to use a GaAsFET preamplifier for EME, beating the G3OUR group at Oxford by a couple of weeks.

Another preamp made from a GAT device was also used in the preamp of the system I used to demonstrate, at about the same time, the possibility of using space debris as a passive reflector by scattering my SSB off a Russian COSMOS launcher in a decaying orbit. That was received by SM6CKU, near Gothenburg, at about 1600km. That wouldn't have been possible without the computing assistance of John Morris G4ANB. We seem to have achieved a World first, and felt we were creeping towards a completed QSO. However, those tests came to an abrupt end when our source of ephemeris data was pulled by a research establishment at Slough ...

73

Chris G4DGU

PS. Apologies to anyone reading this who has seen me comment on these tests before. I remain very proud of what we did at that time, and it is in the nature of the hobby for tests like those to become forgotten.


Clive Elliott GW4MBS
 

I still have this which I think is a GAT3, given to me 40+ years ago by either G3YGF or G3JVL. At the time I was living in Hampshire directly under their tropo path & gave me good experience in looking for weak signals. In fact I have to thank Julian for the nudge to take up CW to make full use of weak signals, hence my change in callsign.
--
Clive GW4MBS (ex-G8ADP)
Pottering on 6m - 3cm in a valley in IO71XW where any QSO is a triumph of optimism over geography!


Andy G4JNT
 

The red spot and black spot FETs used in the G3WDG 10Ghz transverter from the 1990s were Plessey discards.
Presumably what the GATs morphed into after several years of R+D




On Wed, 9 Jun 2021 at 21:53, Clive Elliott GW4MBS via groups.io <humber1ton=btinternet.com@groups.io> wrote:
I still have this which I think is a GAT3, given to me 40+ years ago by either G3YGF or G3JVL. At the time I was living in Hampshire directly under their tropo path & gave me good experience in looking for weak signals. In fact I have to thank Julian for the nudge to take up CW to make full use of weak signals, hence my change in callsign.
--
Clive GW4MBS (ex-G8ADP)
Pottering on 6m - 3cm in a valley in IO71XW where any QSO is a triumph of optimism over geography!


Julian, G3YGF
 

Chris,
Yes, I think it was 1979. We used a GAT5 to get a 0.5dB preamp for G3OUR's 432 EME system, measured with the aid of liquid N2. If I remember correctly, the input circuit was about 3" of 1" wide copper foil stripline... It was written up in the Dec 80 Radcom.
About that time, we also obtained a ceramic substrate and chip with about 12dB gain on 10GHz to help us listen for G3JVL from GM land - all supplied courtesy of the same Dr Cripps/G3WDG/Plessey - again, many thanks!...
We rapidly learned a lot about LNAs, GaAsFETs, and the importance of making up reliable cables and T/R sequencing systems...
I think G3WDG wrote up a 1.3GHz version of the GaAsFET in Radcom shortly after.

I also recall a visit to G3LTF around that time, and his comment on our 432 GaAsFET was something like - "Ok, but you had it easy - I was getting similar results from a paramp, with a varactor pump at 10GHz, some time ago!".

<end of reminiscences>!

Julian, G3YGF

On 09/06/2021 20:40, Chris Bartram G4DGU wrote:
Hello Paul,

I did use a GAT3 and GAT5 at one time
I can't resist a comment on that ... So did I! I seem to remember using a GAT2 and GAT3 and maybe a GAT5. They taught me a lot about the need to get good T/R switching isolation, and to use proper sequencing for the c/o process :-)
.
My source was a certain Dr.(now Prof.) Cripps (ex-G3TPF) via Charlie, G3WDG. In about 1979 mine were used in a preamplifier for 432MHz EME, and very much from memory I achieved a noise figure of around 0.7dB measured by a thermal hot/cold source. that was more than 0.5dB better than I'd achieved with a then state of the art bipolar transistor. With my then 8 yagi antenna and about 700W from a K2RIW amplifier I could hear my own echoes most of the time. I also worked most of the stations then active on the band on CW, although Faraday wouldn't cooperate for a few. I think I was the first UK station to use a GaAsFET preamplifier for EME, beating the G3OUR group at Oxford by a couple of weeks.

Another preamp made from a GAT device was also used in the preamp of the system I used to demonstrate, at about the same time, the possibility of using space debris as a passive reflector by scattering my SSB off a Russian COSMOS launcher in a decaying orbit. That was received by SM6CKU, near Gothenburg, at about 1600km. That wouldn't have been possible without the computing assistance of John Morris G4ANB. We seem to have achieved a World first, and felt we were creeping towards a completed QSO. However, those tests came to an abrupt end when our source of ephemeris data was pulled by a research establishment at Slough ...

73

Chris G4DGU

PS. Apologies to anyone reading this who has seen me comment on these tests before. I remain very proud of what we did at that time, and it is in the nature of the hobby for tests like those to become forgotten.







John Fell
 

Julian,
You and Charlie published a paper including a low noise GaAsfet 1296MHz preamp design , using a cavity and res line arrangement .(Low noise UHF Amplifiers using GaAs FETs )  .The References (6) "A GaAs FET preamplifier for 432MHz with 0.5dB noise figure , Radcom December 1980 "  (G3WDG and G3YGF ) is included .

I built the Radcom published 432MHz preamp , using an unpackaged GAT6 obtained from a visit to Caswell cica 1982 .You found it hooted and did a few decoupling mods at Roke and it survives (with a more modern device ) to this day .
I also have some Gunns and Varactors donated from the Caswell Labs .

73
John
G0API

On Wed, 9 Jun 2021 at 23:35, Julian, G3YGF <julian@...> wrote:
Chris,
Yes, I think it was 1979. We used a GAT5 to get a 0.5dB preamp for
G3OUR's 432 EME system, measured with the aid of liquid N2. If I
remember correctly, the input circuit was about 3" of 1" wide copper
foil stripline... It was written up in the Dec 80 Radcom.
About that time, we also obtained a ceramic substrate and chip with
about 12dB gain on 10GHz to help us listen for G3JVL from GM land - all
supplied courtesy of the same Dr Cripps/G3WDG/Plessey - again, many
thanks!...
We rapidly learned a lot about LNAs, GaAsFETs, and the importance of
making up reliable cables and T/R sequencing systems...
I think G3WDG wrote up a 1.3GHz version of the GaAsFET in Radcom shortly
after.

I also recall a visit to G3LTF around that time, and his comment on our
432 GaAsFET was something like - "Ok, but you had it easy - I was
getting similar results from a paramp, with a varactor pump at 10GHz,
some time ago!".

<end of reminiscences>!

Julian, G3YGF


On 09/06/2021 20:40, Chris Bartram G4DGU wrote:
> Hello Paul,
>
>> I did use a GAT3 and GAT5 at one time
>
> I can't resist a comment on that ... So did I! I seem to remember
> using a GAT2 and GAT3 and maybe a GAT5. They taught me a lot about the
> need to get good T/R switching isolation, and to use proper sequencing
> for the c/o process :-)
> .
> My source was a certain Dr.(now Prof.) Cripps (ex-G3TPF) via Charlie,
> G3WDG. In about 1979 mine were used in a preamplifier for 432MHz EME,
> and very much from memory I achieved a noise figure of around 0.7dB
> measured by a thermal hot/cold source. that was more than 0.5dB better
> than I'd achieved with a then state of the art bipolar transistor.
> With my then 8 yagi antenna and about 700W from a K2RIW amplifier I
> could hear my own echoes most of the time. I also worked most of the
> stations then active on the band on CW, although Faraday wouldn't
> cooperate for a few. I think I was the first UK station to use a
> GaAsFET preamplifier for EME, beating the G3OUR group at Oxford by a
> couple of weeks.
>
> Another preamp made from a GAT device was also used in the preamp of
> the system I used to demonstrate, at about the same time, the
> possibility of using space debris as a passive reflector by scattering
> my SSB off a Russian COSMOS launcher in a decaying orbit. That was
> received by SM6CKU, near Gothenburg, at about 1600km. That wouldn't
> have been possible without the computing assistance of John Morris
> G4ANB. We seem to have achieved a World first, and felt we were
> creeping towards a completed QSO. However, those tests came to an
> abrupt end when our source of ephemeris data was pulled by a research
> establishment at Slough ...
>
> 73
>
> Chris G4DGU
>
> PS. Apologies to anyone reading this who has seen me comment on these
> tests before. I remain very proud of what we did at that time, and it
> is in the nature of the hobby for tests like those to become forgotten.
>
>
>
>
>
>
>
>