I cant run 6m WSPR again for a while, as I need to put the station back to HF use. But it started me thinking about the possibility of a permanent 50MHz QRP WSPR beacon.
If I follow a DSB architecture, then the circuits are fairly simple. If I aim initially for Tx only then even easier. One of my SBL-1 DBMs will serve as modulator, a simple audio buffer amp ahead, and followed by a small chain of linear amplifiers up to, say, a few watts, and an efficient low pass filter.
The big issue of course at 50MHz will be frequency stability. How to generate 50.293MHz, in a way that will remain accurate? Well, I thought, I could start at 10MHz, pulled a little, and use a multiplier to extract the 5th harmonic. But how to ensure stability? Ah, perhaps a good use for one of these -
This is the 10MHz TCXO from an old Marconi RC-690 public safety radio. I have at least two of these, although one is still attached to the rest of the RC-690! This, followed by a tuned buffer amp at the 5th harmonic (50MHz) should give me the accurate and stable LO signal needed. The only problem is I dont know the pin-out of this beastie! Luckily the other one is still on the RC-690s control board, so I should be able to trace the connections out.
Whether I will be able to pull one of these far enough I dont know yet. IF not, then a more complex oscillator chain might be called for.