Thursday, August 06, 2020

Logging noise floor with hamlib

From time to time I see terrible interference right across HF and even up to VHF here. Sometimes it comes on for under ten minutes and while I make a note in the log when I see it, automatically logging the noise level seems like a good way to find out if there is a regular pattern.

At this point I haven't satisfactorily visualised the problem but I wanted to leave a note about progress so far.

Here's a graph of one minute samples of the S meter reading on 40m for the past few days. Times are local.

The values are read via a USB CAT interface to a Yaesu radio tuned to 40m. The values seem to be roughly S4 = 400.

I use the hamlib command line utility rigctl to do the real work.

To log these values I have a cron job that executes every minute and runs this script:

The resulting log file looks like this:

There's a tab between the date/time and the value.

To draw the graph, I use Gnuplot running this little script.

So far this isn't clearly showing when the interference is "on". Possibly the logarithmic Y scale doesn't help. I think it's interesting to see the noise floor measurements but they vary widely and I think the next step might be to take multiple measurements each minute and perhaps log the average or minimum.

Here's the graph of an additional day but with five quick readings taken and averaged each minute. Still not a clear result.

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