Re: GATs


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.






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