[NLRS] 222 Beacon

[Doug Reed]

Hi Bill.

I've been looking at the U3 kits for quite a while. I have one of the
original kits for 30M and bought a U3S most recently with his homebrew
SI5351A OCXO board and GPS receiver. I bought it mainly because of the
higher frequency range. But you do need the OCXO board if you want to
output on 6M or above for WSPR. It needs the extra stability. I think
that what I like best is the way he adjusts the TX frequency based on
GPS timing and even calculates the grid square for WSPR.

Are you using a DEMI transverter to get to 222MHz? I would guess you
might need some more filtering to keep the out-of-band crap low? The
SI5351A doesn't go to 222MHz and stability isn't that good above 12M
without the OCXO board. You might be able to use the second or third
oscillator output to replace the LO crystal in the transverter and
then you should have maybe 10e-8 accuracy for the beacon
frequency.....

I've been thinking in terms of using a U3S to drive the TX crystal
input of a surplus FM transmitter to get a fairly high-power beacon.
The FM transmitter gives filtering and higher frequencies and power.
The U3S gives stable reference frequency and all the modulation
options, within the limitation of class C amplification with the FM transmitter.

A couple years ago I asked Hans about adding PSK31 capability to the
U3 kit, but he replied that PSK31 requires some analog component to
the RF to achieve minimum bandwidth. He could generate something that
would decode like PSK31, but it would be wider than 31Hz. All the
other modes he supports with the U3S don't require that analog
component and work fine with class C.

<http://rudius.net/oz2m/ngnb/pi4.htm>
You might want to consider some variation of the PI4 beacon mode. It
can be done with the U3S and uses the IARU 1 minute format favored in
Europe. It used JT4 mode for beacon telemetry, CW or FSK-CW for ID,
and about 20 seconds of carrier. About the only thing it doesn't do is
multiple power levels. I considered using multiple 1 minute beacon
formats but that would probably just be more hassle to decode.

If you are using a transverter to get to 222MHz, you can use the band
outputs of the U3S to control an attenuator between the U3S and the
transverter. It is harder to get adjustable power output with an FM
transmitter. The best option I can think of would be to use an
external attenuator after the transmitter, but then you have relay
problems or need to build a high-power multi-section RF PIN
switch..... I've always wanted to have maybe two short 10dB power
steps near the end of the carrier period. It might be better to do
0dB, -20dB, -10dB, 0dB, off? Yes, I like that option.....

73, Doug Reed, N0NAS.