I have noticed two oddities looking at the signal data reported by my "Sundtek MediaTV Digital Home USB Tuner Cable/Terrestrial HD (DVB-C/T/T2) " tuner as follows:

(1) The SNR values (in dB) are too high - theory says that the lock threshold should be around 20 dB rather than 80 dB indicated by the results below.

(2) The SNR in dB, the SNR expressed as a percentage of expected maximum, and the AGC always seem to have the same value.

The results were obtained using the OpenWebIf "/web/signal?AGC=" command.

Results from an Si2169 tuner (which are believed to be correct and others have found them to agree with two other models) are included for comparison".

One (and only one) terrestrial mux deteriorates when it rains, this is one of the reasons why I'm investigating these values....

Good mux, no rain, Si2169

<?xml version="1.0" encoding="UTF-8" ?>
- <e2frontendstatus>
<e2snrdb>36.70 dB</e2snrdb>
<e2snr>73 %</e2snr>
<e2ber>0</e2ber>
<e2acg>0 %</e2acg>
</e2frontendstatus>

Same good mux, no rain, SundTek

<?xml version="1.0" encoding="UTF-8" ?>
- <e2frontendstatus>
<e2snrdb>100 dB</e2snrdb>
<e2snr>100 %</e2snr>
<e2ber>0</e2ber>
<e2acg>100 %</e2acg>
</e2frontendstatus>

Susceptible mux, levels starting to fluctuate, Si2169

<?xml version="1.0" encoding="UTF-8" ?>
- <e2frontendstatus>
<e2snrdb>30.14 dB</e2snrdb>
<e2snr>60 %</e2snr>
<e2ber>0</e2ber>
<e2acg>0 %</e2acg>
</e2frontendstatus>

Susceptible mux, levels starting to fluctuate, SundTek

<?xml version="1.0" encoding="UTF-8" ?>
- <e2frontendstatus>
<e2snrdb>88 dB</e2snrdb>
<e2snr>88 %</e2snr>
<e2ber>1</e2ber>
<e2acg>88 %</e2acg>
</e2frontendstatus>

Picture goes almost completely at 82dB, BER shows low values in OpenWebif, but oscillates between 0 and 199999 in SignalFinder.

Si2169 shows this with picture almost gone...

<?xml version="1.0" encoding="UTF-8" ?>
- <e2frontendstatus>
<e2snrdb>20.97 dB</e2snrdb>
<e2snr>41 %</e2snr>
<e2ber>0</e2ber>
<e2acg>0 %</e2acg>
</e2frontendstatus>

BER stays at 0 in SignalFinder.

Both tuners were LOCKing in and out every second or so.