Dear Ham Fellows,
I've started to do some experiments with QO-100 using my IC-7300 transceiver. As it is my main base transceiver and I do not own the 9700 nor any VHF/UHF SSB gear, the main scope of this project was to build a transverter for this use case, yes NB. First of all I've built a downconverter to 28MHz and an upconverter using the same architecture. It quickly turned out that the upconversion is a real problem due to the image frequency on the 2.4GHz band (second mixing harmonic 28MHz away only 9-10 dB lower, so, useless...).
Second attempt on which I'm currently working now:
- Use the 6m band from the transceiver at 52MHz
- Use two local oscillators; LO1 @Rx running at 687.5MHz, @Tx running at 659MHz and use LO2 @Tx only running 1689MHz. Therefore Tx is performed with dual conversion having the IF at 711MHz.
- For 711MHz I found a very good helical filter with 3 cells and 5MHz BW. https://temwell.shoplineapp.co…ndpas-filter-tt6814a-711m
- Results so far are good no spurs in the band of interest
Some challenges encountered so far:
- LO1 and LO2 are done with ADF4350 to keep low the phase noise the phase and frequency comparator (PFD frequency) runs at 12.5Mhz (of course that has the disadvantage of high 100kHz channel spacing but based on my measurements produced the lowest noise)
- Next to implement external reference, GPS based, Leo Bodnar miniGPS (received today) clock feed references for the ADF's.
Some problems which are unanswered and maybe you can share your experience and possible solutions for these:
- Despite the fact that I acquired the Bullseye LNB, claiming very high stability, it is 20-25 KHz offset from the expected LNB's LO frequency. Secondly, it drifts very annoyingly and this is noticeable with FT8 reception. (no warm-up issue)
- Okay I've found a method how the recenter to the correct frequency the LNB's LO (here: https://github.com/g4eml/Bulls…r/blob/main/Schematic.pdf) but what about drifting? I know has on output of 25MHz but to counteract at LO1 would mean to change the channel spacing to far lower which would have as consequence 20-30dB higher phase noise. How to steer this drifting?
Thank you for reading, I highly appreciate any observation, regards and 73's by YO6OGJ, Endre