[NLRS] Thoughts on VHF-UHF beacon hardware.

[Dr. Gerald N. Johnson]

Many of the more recent FM two way radios are programmable for 
frequency. Might need some modification to make them send CW but nearly 
always they have a power adjust circuit and that should key the output 
decently. If not keying the power to a couple more stages should 
minimize the backwave.

Most FM receivers are linear until just after the filter that sets the 
receiver bandwidth, if they weren't linear that filter would be 
ineffective at rejecting strong adjacent channel signals. So the 
SoftRock or other SDR could be connected just before or after the filter 
to allow wide or confined frequency coverage.

73, Jerry, K0CQ

On 7/16/2015 12:14 PM, Doug Reed wrote:
>
>
> I've been debating with myself what might be the cheapest way to get a
> VHF-UHF beacon on the air without having to dedicate an expensive SSB
> rig to the task and without buying crystals. I keep coming back to
> using modes like CW or PI4/JT65/WSPR that work with a Class C RF
> amplifier, then use an old FM mobile as the TX and power amp. You can
> use crystal control, but crystals are getting difficult and expensive
> to buy. But it is fairly easy to do if the beacon controller also
> provides the frequency control and stability. The HansSummer.com
> Ultimate 3S controller can handle all of that, especially with the
> optional OCXO SI5351A oscillator and using GPS for frequency control
> and timing.
>
> I've been a bit more worried about how to do propagation RX monitoring
> from the same site, if I wanted to.... The FM receiver is useless for
> that, but with the SI5351A oscillator acting as a LO for the receiver
> front-end and mixer, I could feed the IF out to a "cheap" HF receiver
> such as a SoftRock, Minima, Pixie, or even a CB SSB radio. Anything
> that receives CW or SSB would work to feed audio to the sound card RX
> software for decoding. Another option would be to just use the FM
> receiver front-end as a filter with a RTL-SDR dongle as the
> receiver....
>
> If anyone wants to try this or other direct keying mods to build a
> beacon site, VHF and UHF crystal-controlled mobiles are available
> pretty much for the hauling. Nobody wants to buy crystals. 6M is a
> little harder to find because you have to be sure you get a "high
> split" radio.... In fact the problem may turn out to be that many or
> most of these mobiles are 110W radios and they seem like a bit of
> overkill for a beacon....
>
> One thing to remember, the FM mobiles were designed for intermittent
> duty, around 20% TX. Unless you reduce power, add fans and heat
> sinking, or built an intermittent TX beacon, you will have problems
> with overheating the TX. OTOH, I have successfully modified a 110W GE
> mobile to run FM repeater continuous duty with just extra heat
> sinking. I then added fans to be 100% certain and it ran for about 15
> years before being replaced with newer equipment.
>
> 73, Doug Reed, N0NAS.
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