Hi Andy,
1. The Dual PB/APF button has multiple functions. First of all, it is
different in CW than in RTTY, and it doesn't do anything in other modes
(SSB, DATA A, etc.).
In CW, the Dual PB button has two functions, depending on whether
CONFIG:DUAL PB is set to APF or NOR.
In the APF configuration in CW, it is a very narrow audio peaking
filter. Tuning of signals is touchy - even a 10-20 Hz change can make
the difference between copy and no copy on a weak signal. The APF
doesn't do much for strong signals - it's for pulling very weak CW
signals out of the noise.
In the NOR configuration in CW, the dual PB filter gives you a "stepped"
filter bandpass, with a 150 Hz center portion set within a broader
"context" bandpass about 20 dB down from the central bandpass; the width
of the broader "context" bandpass is controlled by the WIDTH control.
The effect is most obvious when WIDTH is set wide, say to 700-1000 Hz.
Without the DUAL PB, signals several hundred Hz away but within the
bandpass are strong; with DUAL PB, they are attenuated but still
audible, although not as strong as signals within the narrower central
bandpass; when WIDTH is narrowed down, with or without DUAL PB signals
that far away become inaudible. When WIDTH is at, say, 400 Hz or so, the
effect of the DUAL PB setting is not quite as obvious - the stepped
response is not all that different from what you may be used to using
normal crystal filtering without DSP.
In RTTY (FSK D or AFSK A), the Dual PB button gives you a dual peak
filter peaked on the two tones of the RTTY signal. In theory, this
actually degrades the performance of a well-designed demodulator, so you
might be better off not using it routinely, but in the situation where
there are two overlapping RTTY signals with the mark or space of the
interfering signal in between the mark and space of the one you are
trying to work, it may help reduce the interference.
2. I can't help with NR.
3. KPA3 temp: at 41C, from a thermal point of view your PA is loafing.
In heavier use (RTTY or heavy CW contesting use), it will climb up into
the 50s or even the low 60s (depends on the ambient temperature, of
course), and the fans will speed up. You can hear what the fans sound
like at the different speed levels by using the CONFIG:KPA3 menu and
changing it temporarily from NOR to FN1, FN2, FN3 or FN4. I don't think
I have ever gotten my PA temp high enough to switch to the FN4 level
automatically (somewhere around 65-70C, perhaps?), but I have reached
the FN2 and FN3 levels during contests (FN3 mostly in RTTY). The KPA3 is
supposed to protect itself by shutting off at 84C, but I've never seen
anything approaching that level.
You may see the PA TEMP indication change slightly during transmit as
compared to receive. I believe this is caused by the voltage difference
between TX and RX (if for no other reason than resistive losses in the
power cable). You can set the PA TEMP display to RX-only if necessary to
avoid this effect.
73,
Rich VE3KI
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