[Mich VHF UHF Society] Filtering for beacon PA

[Steve Cox]

I am running my IC 7300 with a switching psu - an Alinco DM-30T which has a
noise offset control which works very well and allows me to dial out any
switch mode noise that comes from the power supply. This unit seems to be
very clean in that regard and I seldom need to adjust the noise filter, and
it cost me about $135.00 so I think for your needs (probably way over the
amp requirements) I would get one of these Alincos with the noise offset
circuit.
73,
Steve~W8SFC


On Tue, 7 Apr 2020 at 15:13, Patrick Thomas <p-thomas at mindspring.com> wrote:

> Hi all,
>
> Some of you might recall that I had a 222 beacon on the air for a while...
> which I took down due to a couple of problems... mostly the ~1khz drift,
> and also some HF QRM, presumably from mixing with the switching power
> supply.
>
> I had been meaning to move to a newer (digitally synthesized, different
> mode) type of beacon anyway, and finally have gotten to a point where I am
> on the right track... hopefully will be putting the GPSDO and OCXO boards
> together this week while on "vacation" from work so I'm hoping it will be
> back on the air very soon.
>
> The downside is that the power out from the RF stages is very low.  I have
> found a surplus Motorola 220 radio which has a PA section I believe I can
> borrow which will boost it to the ~15W range, which is "about right" I
> would say.
>
> Buuut... I also am really concerned about the noise issues from before,
> especially if using an amplifier, as I would like to get away with a
> switched power supply but I know there will also be a lot of noise due to
> the microelectronics.  Can someone suggest an appropriate type of filter
> that might be appropriate here?  I know a cheap-and-dirty high pass is
> customary, but I am wondering if this might dictate something a little more
> exotic, particularly as it will run "unattended" for some time.  I would
> also think some filtering after the PA may be appropriate, though this
> doesn't seem to be especially common.
>
> What do y'all think, in this case?
>
> Thanks,
>
> Pat
> KB8DGC
>
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