I am thinking building a version of my single band single band 40 Meter SSB transceiver? to work on 60 meters, but have to carefully choose an IF frequency.
The current IF frequency for te 40 meter version of the rig is 12.288 MHz.
Since it uses the Si5351 you have to be careful about the odd and even harmonics emitted.
A. For an IF of 12288 kHz:
2x the LO will be 10400-10800 kHz
3x the LO will be 15600-16200 kHz.
4x the LO will be 28352-29152 Khz? [10 meter ham band]
5x the LO will be 35440-36440 kHz
Analysis (All frequencies in kHz):
1. If I design the transceiver to tune from 5200-5400 kHz, then the LO will be in the middle of the 40 meter ham band at 7088-7288 kHz [regrettable, but livable I suppose].
2. 3rd order product (remixing, 3*LO-tx frequency) due to non exact impedance matching in the TX mixer: Low 15600-5200 =? 10400 High: 16200-5400 = 10800. Looks good
3. Closeness of LO to band (for effective filtering) 7288-5400 = 1888. Hmmm. Mediocre. May require a higher order post mixer filter.
B. For an IF of 9000 kHz:
2x the LO will be 7600 to 8000 kHz
3x the LO will be 11400-12000 kHz.
4x the LO will be 15200-16000 KHz
5x the LO will be 19000-20000 kHz
Analysis (All frequencies in kHz):
1. If I design the transceiver to tune from 5200-5400 kHz, then the LO will be in the middle of the 80 meter ham band at 3800-4000 kHz [regrettable, but livable I suppose].
2. 3rd order product (remixing, 3*LO-tx frequency) due to non exact impedance matching in the TX mixer: Low 11400-5200 = 6200 High: 12000-5400=6600 . Unacceptable, would require a very high order filter.
3. Closeness of LO to band (for effective filtering) 5400-4000 = 1400,? Poor. May require a higher order post mixer filter.
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So the choice appears to be 12288 kHz for the IF, unless someone can suggest a better IF frequency with readily available crystals.
If anyone has built a 60 meter SSB transceiver, I'd like to know what IF frequency you chose and why.
Steve
WA6ZFT
hwstar