Re: G3WDG 10 GHz TX converter

Chris G8BKE


I've had similar experiences to David, having built two of these
units over the years. Using the correct absorbing rubber as sold by
Charlie himself, in the lid of the box, trackside, plus careful
adjustment of the pots to keep the gain in check also helped. I found
that the setting of RV3 most critical, in this respect as this
controls the drain supply to F2.

Small pieces of the same rubber glued to the pcb close to the copper
tracks in areas which seemed sensitive to "finger effects" also
helped. Both mine DO operate with their lids on, as it does help to
avoid pick-up from adjacent units.

Its a fiddle but worth the effort!

73 de Chris G8BKE

--- In, "David Wrigley"
<davidwrigley@m...> wrote:

Hi Kevin

I had the same problem - just reduce the gain of some of the stages
with the
bias pots. In my case I know that I didn't use the originally
specified FETs
- they were later and higher gain types. It looks like the layout
won't cope
with high gain. I also found other issues.

1. Placing a lid on the Tx converter caused it to oscillate -
because the lid was creating a waveguide back to the earlier
stages. I tried
pieces of rubber and wood to try to absorb the energy but nothing
worked -
so leave the lid off was my solution.

2. Looking at the output with a spectrum analyzer there was a
amount of LO output. Apparently this doesn't get through the pipecap
filtering. It just hops across the board from the multiplier. By
fitting a
vertical screen along the board between the multiplier and the
output FET
chain, this can be significantly reduced. It can be also pretty
eliminated by fitting an external waveguide filter.

It seems like the idea of putting all that action on one board
introduced a
few difficulties and a better system would have used external cavity
filtering between separate screened boxes. However having said
that, with a
few modifications (better post filtering and a lower NF preamp) it
works well and I still use mine.

73 David G6GXK

-----Original Message-----
[] On
Behalf Of zl1ujg
Sent: 31 January 2006 05:42
Subject: [ukmicrowaves] G3WDG 10 GHz TX converter

A friend of mine has built a G3WDG 10 GHz TX converter.
he has found it is highly unstable with oscillations near final
frequency (+/- 1 GHz).
He has resoldered the devices and probes and checked voltages, but
anytime he tunes it up for optimum o/p on 10368 MHz, it takes off.
can remove the IF drive and its merrily oscillating to itself.
Devices are Plessey Black spot.

I know many of these units have been built in the UK.
Help please.


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