HFU HF Underground
General Category => General Radio Discussion => Topic started by: ChrisSmolinski on December 05, 2013, 1248 UTC
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Here's a graph of Happy Hanukkah Radio's signal strength during their 4 December 2013 transmission. The graph starts just before sign on, and runs until just after, so you can see what the background noise levels were like. They were about S4/S5 at sign on, and S3 at sign off.
HHR's signal was S8 at sign on, and it dropped to S5, at which time it was barely audible. It then quickly came back up, to roughly S9 with some peaks above that, and remained excellent until sign off.
One thing you can take from this is that even if you are not hearing a station others are reporting, it pays to continue to listen, as propagation can dramatically change in a matter of minutes.
(http://www.radiohobbyist.org/blog/mypics/Happy_Hanukkah_Radio_Signal.png)
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How did you make that chart? Its really cool!!
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How did you make that chart? Its really cool!!
mySdrPlayback, an app I wrote, demodulates the I/Q SDR recording file, and produces a text file with the signal strength every second: http://www.blackcatsystems.com/software/sdr_iq_recording_playback_program.html
I then imported that into Excel to produce the graph.
I really should modify mySdrPlayback to add a timestamp to each line in the text file, so I can make the X axis in graphs something rational like the actual time.
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That's awesome! I should get the app.
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I have seen a few different ways to do similar stuff, both with SDR's and with conventional radios. Here, for conventional radios like the Icom R-75 and R8500 I have a very crude Visual Basic program that will take a list of freqs, tune to each in turn, grab the signal level of each, and write the results for each freq to a CSV file. I can then open that file in Excel and chart the results. For all of my WinRadio gear I have a similar thing, but using the WinRadio supplied RBASIC environment that is part of the WinRadio GUI. Again, it looks at a list of freqs, samples each in sequence, and writes the results to a CSV file. I can tell it how long to wait before it starts scanning and also how long I want it to scan. I can also control the sample rate, from once per second or less to once every few minutes if I want.
The results look something like this:
(http://www.pbase.com/token/image/153659766/original.jpg)
In this case I have parsed the 10 frequencies it was checking down to only 3 to show here. 2 are active with V24 transmissions, one is not.
I can do the same thing on recorded SDR files, however the playback and sample has to be one to one time with my technique. Not quite as fancy as Chris's, but the programs I use were written by someone with no software background...me.
T!
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Nice Token,
A while back, I had pressed my old SDR-14 into service to monitor an assortment of frequencies 24/7. It ran in real (30 MHz) mode, and performed an FFT on the incoming data. You can't demodulate a signal, but it was completely adequate for determining the signal strength. The advantage was it could monitor any number of HF frequencies, I just had to edit a text file list of them. It would then update a web server every minute with the data. You could pick a frequency, and see the last 24 hours of signal strength.