Signal to noise calculation dB

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W5XTT's picture
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Joined: 2016/02/27 - 16:09
Signal to noise calculation dB

I have noticed that reducing the filter bandwidth on my radio has a considerable impact on the dB (signal to noise ratio ?) of a particular signal that I receive. I'm wondering, is that number is calculated by averaging the power in the full bandwidth/hz of the decoder compared to the signal of the particular station / Hz. If it is, it would seem that if you are listening on a busy frequency where there are lots of stations transmitting, that your reported received signal dB might be lower than if you are listening on a quiet night when there are not so many stations transmitting. If that is the case, the dB number is not really a reference to noise floor, but signal to noise + all other signals ratio. Would it be possible to use the short period before the transmission period begins to perform a NOSIGNAL noise average. Each received signal during that following period could then be compared to the "Noise" level giving the operator a better idea of how their station is performing, regardless of how many other stations are on at the time?

Don't know how your decoder works, but if you are comparing levels in the 4 expected frequencies to find the max above the average...the average of the 3 unused frequencies should relate well to the noise floor, especially if you average them over the entire reception time. you could evel do statistical variation on the noise samples and reject spikes that way...Just something to think about.

Thanks. This is a wonderful service that is being enabled here. Truly fascinating to watch.
ICOM 7610, dipole, 5 watts