Improving the FRG7 selectivity by replacing filters is problematic when going much beyond a 3-4 kC bandwidth and expecting improved SSB reception. The cause is the Yaesu? free running BFO is just not stable enough to remain in the narrower passband, if set for cold mornings, it will drift away as the day warms. To do a successful upgrade requires the BFO to be upgraded also with at least ceramic resonators to prevent BFO drift, this is a much more invasive modification.?
My FRG7 has been fully modded in this regard, I did this back in the 80s and will post pics later. The filters are diode switched using the existing mode switch, the AM/ANL position selects the narrow filter in AM mode, and is automatically selected also when in SSB/CW modes. Using existing switches save defacing the radio. The existing filter was removed and two new filters were mounted on a small daughter board. Diode gating? is used, this only requires a DC voltage and not signal voltages to be switched, making an easy job of it..
The existing BFO components were removed from the PCB and a small replacement PCB was constructed and mounted in its place.....a? one transistor oscillator stage does the trick. the ceramic resonator is capacitively loaded for the USB position.
With this done, the radio easily will hold a commercial SSB station correctly tuned for hours on end, mine spends much of its time on the Pacific aircraft? net on 8867 kHz.
Other mods I have done include synch AM detection, very easily added to this radio and? very simple improvements to the RF circuitry, including an AGC mod that includes the first IF amplifier into the AGC loop for enhanced gain control preventing cross mod on strong stations in the second mixer.
. Another very worthwhile and simple? improvement is the removal of the third IF emitter bypass capacitors, this lowers the excessive gain and noise level, and prevents frequency "skewing" at high signal levels, by introducing localised negative feedback.?
The AGC is also automatically slowed when in SSB modes.
Many of these mods are possibly of academic interest only, but mentioned here? out of completeness.
I can supply schematics if there is any interest in going this far.
