Hans,
Wow, that is pretty low output!? I think the VHF fet in the 5W PA
needs 50mw for
adequate drive.
Well, thanks for the reply, but what about the +V for the U3S
supply, should I use +12V ???
I already figured the components on the U3S for 2M were not
adequate.? I changed the inductor
feeding the BS170 drain to around 450nH, then changed the caps
involved to 0.001uf instead of
0.1uf.? A friend told me he made up a U3S for another guy on 2M.?
He never mentioned any mods to
be done.
Regarding the scope, well it is a 100Mhz Rigol, but shows a
pretty decent signal on 2M.? I was able to
see some clipping when adjusting the bias, so backed off until it
looked clean.? Sounds good on the 2M
rx...
73
Glen K4KV
On 8/9/2018 01:41, Hans Summers wrote:
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Hi Glen
It's been some years since I tried a U3S on
2m. It was before the change to the bifilar output
transformer. It could be worth trying it also with a single
winding inductor.
My power output was 14mW (zero idle current
adjustment) and could be pushed to 17mW with higher gate
bias.
As Alan said - do you believe your scope and
probes? If a 'scope is what you used? You'd need a pretty
good setup to get any decent accuracy on 2m. In my case I
used a spectrum analyzer for the measurement and I was
reasonably confident in it.
73 Hans G0UPL?
?
> I
am having trouble getting power out on 2M (using it as a
beacon).
>
Glen,
I'm not aware much has been said about 2m operation.
> I see 200mv on the collector of the BS170 fet with 5V
on the drain.
>
200mv on the gate? I'd expect it should be higher but
capacitance must
be high for 2m. Are your scope and probes good for 2m?
> I peaked the output adjusting the bias, for a clean
looking signal on
> the scope.
>
I thought the bias was adjusted to the point that the FET
just begins to
take current. You do not say where you look on your scope
but it is
squarish waves around the FET. Not until after the LPF
will it look clean.
Sorry, that's about all I can say.
73 Alan? G4ZFQ
> Am I supposed to use +12V on the U3S PA+ line?
>
> The 5W PA does amplify the signal, but I fear the
drive power is too low.
>
> I do have the VHF fet in the 5W PA board.
