[Mich VHF UHF Society] Filtering for beacon PA

[David DeVos]

Hi Patrick,
I currently have a 220 beacon running in EN63wu, on the West side of the state.  If you are worried about spectral purity, I've seen some cavity filters for 220MHz from China.  I'm running an old crystal FM rig on 220 that was modified to send pretty good CW, and a small amplifier running 20 watts.
I certainly wouldn't worry about 1khz of drift.  I'm curious what frequency you are going to be on.  The KF8QL/B is on 222.058.
I attached some photos.  

 
Dave DeVos KF8QL
616-278-8068 - mobile


 

    On Tuesday, April 7, 2020, 03:13:26 PM EDT, 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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