[TenTec] 2.041XL: Findings and opinions
linbdavis at earthlink.net
Sat Feb 28 10:26:03 PST 2009
Here are some findings and opinions with the 2.041XL. I used spectrogram software (Spectrum Lab) to measure/observe aspects of the behavior.
When AF AGC is invoked, there is a full 20 dB drop in audio output.
Slow-acting AN. Not necessarily a show-stopper though.
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.
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.
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,
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