I believe the problem is that transceiver's used for digital service are still designed, not for digital service, but for SSB and CW in which AGC is used:
1. To prevent "blasting" by strong signals when you are trying to hear weak ones. 2. To protect the last IF amplifiers and detector from overload distortion. The typical receiver designer still strives for as "flat as possible" curve of input level vs audio output. In the later PSK-20 versions, I removed all the AGC and the PSK-20 can operate within 100 Hz or less of an S9 signal with no loss of characters or darkening of the waterfall (desensitization). The dynamic range of the detector and soundcard is about 54 dB, which is more than the usual range of PSK31signals found (with everyone running 20-30 watts). What good is it to have a receiver reducing gain in response to a strong signal when you are trying to copy a weak one? If you need to copy the occassional very strong station, the RF gain can be manually reduced or attenuation inserted. Narrow IF filters attenuate *nearby* stations, but not truly "adjacent" ones unless the signal you are copying happens to fall near the side of the IF filter and the strong station is just outside the passband. A really good receiver for soundcard digital modes will have BOTH good filtering and passband tuning (when needed) and either good dymamic range without AGC, or a dual-loop AGC system that some manufacturers claim prevents AGC pumping. I don't have one, so I can't confirm how well it works, but if you are in the market for a good receiver for digital modes, I'd first look at the AGC characteristic. In my old IC-761, I can disable the AGC, but then the IF chain distorts too easily. The PSK-20 is much more pleasant to use. Some rigs can run rated SSB power on digital modes, but most of them can only run half rated power at best, for both duty cycle and linearity reasons, so increasing power a lot is not always an option to improve copy on the other end. 73, Skip KH6TY
