Thinking crystals and searching the DigiKey page at the same time, that's what I found:
- standard crystals for 7680 kHz
- SMD crystals for 5223.438 kHz
Doing the maths reveals:
2 x 7680 kHz = 15360 kHz
15360 kHz - 5223.438 kHz = 10136.562 kHz
BUT: 10138.7 kHz - 10136.562 kHz = 2.138 kHz
=> we are off by about 2 kHz.
Remember, this is subharmonic, thus the 2 kHz offset would need a 1 kHz correction at the LO.
The concept would be the following:
- The SSB-filter will be built from the SMD crystals, this allows for a small filter, that even could have it's one casing.
- Regular XO on 7680kHz, pulled up by 1.069 kHz (which should be manageable) as local oscillator.
- A standard J310, or similar front-end, no AGC but some switchable attenuation (RX train).
- Here comes the trick, a subharmonic mixer á la RA3AAE, i.e. two antiparallel diodes (RX train).
- The subharmonic mixer propably also works for TX... If not, a regular doubler is required, in combination with a regular mixer (TX train).
- Some sort of final (TX train).
So many idea, and so little time...
BTW: I am looking for a combination of standard crystals that would get me to 10148kHz. Any idea? Please let me know!