[Icom] IC-775DSP: an undocumented feature ???

[Vladimir V. Sidorov]

Hi all,

Playing with the radio some time ago I've noticed something new for me at
the 775. Supposingly the APF is only working for CW. But apparently if the
button is pressed in SSB mode, it also works. The effect is not as drastic
as in CW, but certainly the overall sound changes itself. It is noticeable
for rather weak signals, only.
It looks like there comes a resonant frequency within the bandpass, and the
resonant is around 1200 Hz what makes the incoming signal more ringing and
more readable. At some weak signals the button works like a switch,
illigible - non-illigible.
The only explanation I can imagine is the fact that switches in the
transceiver are made on pin-diodes. Accordingly there might come leakage of
an incoming signal through the non-fully unswitched diode and the APF
circuit partially remains working.

Before posting this message I have made several checks to be sure, I am
quite far from gallucinating... and for sure there is an effect on weak
signals, as described.

Did anybody else notice the same?

And if somebody wants to repeat my experience, let me remind you once again,
it is only working for weak signals, there is no any difference in receipt
of strong ones.

Thanks and 73,
Vladimir EU1SA