Here are some findings and opinions with the 2.041XL. I used spectrogram
software (Spectrum Lab) to measure/observe aspects of the behavior.
1.
When AF AGC is invoked, there is a full 20 dB drop in audio output.
2.
Slow-acting AN. Not necessarily a show-stopper though.
3.
Very slow acting NR, needs to be 2 to 3 orders of magnitude faster. (The leaky
bucket needs to be a lot leakier.) It would then attenuated noise in between
utterances or slow cw elements. As is, if the tuned signal is above a certain
threshold, the overall sound increases to "full-gain". If the signal input is
decreased some, either by turning off the PREAMP, adding some attenuation or
decreasing the RF gain (or if it decreases naturally), the output audio slowly
fades to almost nothing, so these weaker signals slowly become inaudible. It
takes up to 3 minutes for full gain reduction! (Hint: Use the spectrogram.)
At this point, if a loud static pop/crash or sweeping carrier occurs, the
overall sound level instantly jumps to "full-gain", and the slow gain reduction
begins anew.
This doesn't seem very useful, especially for weak signal work.
There is some difference between levels 1-9, but it fairly subtle.
The other obvious change when invoked is an immediate attenuation of the higher
frequencies.
Further, it appears to be frequency adaptive; an adaptive filter process at
work. It doesn't create a tight filter however, so it doesn't seem to have much
utility unless one operates with their BW much wider than the signal they are
listening to and any extraneous signals within those frequencies outside of the
desired signal are weak or absent. It will maintain the gain of signals in
those frequencies otherwise.
4.
Spectrum shadowing doesn't appear with Color 8, hard to see in 7, and 6, very
distinct in 5, good in 4, ok in 3,2, and distinct in 1.
5.
The waterfall is very nice!
6. With agc decay rate on 5 or below, there is significant popping/ distortion,
as if the decay rate was extremely fast/infinite. This occurs when the AGC is
active. Turn RF gain up and listen to a medium strength varying signal such as
an SSB QSO. Increasing hang time decreases the popping rate, as one would
expect.
7. With AGC decay rate set to 6 and 7, the decay rate is actually 0, and will
hold the last peak value forever. This can be seen by observing the S-meter
while listening to a moderate signal. It will go up, but never go down. With
each strong signal peak, it is pushed higher. This occurs in the SLOW and PROG
AGC modes.
8. I can consistently cause the DSP code to crash with resulting hash issuing
from the speaker, often by just pushing the NOTCH button. Otherwise, by
repeatedly enabling and disabling the NB, NR, NOTCH and AN in random order.
This usually, but not always, clears when going back to RF AGC.
Best to all,
Lin
WB1AIW
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