[TangerineSDR] TangerineSDR Digest, Vol 42, Issue 3

Bob Stricklin bstrick at N5BRG.COM
Tue Sep 6 13:34:43 EDT 2022

Hello Jonathan,

Thanks for posting your information and the plot.

I have been trying to get a “Super SID” receiver running properly recently. I am using the super SID receiver sold by SARA and a loop antenna. I am not convinced the system is working properly yet.
Running a python supersid software package on a RPi3. Data is being collected and I can generate plots of signal strength vs time for VLF spectrum (0-48k). I started out trying to monitor about 10 stations and seems to be flowing fine.
I now feel like my loop antenna needs to be improved with a matching network and I have reverse engineered the circuit on the frontend feeding an audio injector 48K sound card added to the pi. I can see potential improvements in the circuit filter also.
I have some questions about your setup here and the data output…

What VLF receiver is connected to the RPi4 and what type of antenna is being used?

What kind of sound card interface?

What kind of antenna?

In your plot do you feel most of the information is signals or is there a large contribution from noise?

Can you give me an idea what the base level of signal strength is in db/hz or some other units from the receiver?  My system indicates a level of -27 to -32 db/hz although, I have no confidence in this level until I do some calibration testing and I don’t want to stop collecting data to do it.

Also would be interesting to know what three stations your are receiving which are the strongest?

Do you (we) really need to monitor all stations to meet the science goals? If not what would be appropriate? If you do not have any idea that is fine but it is a thought I have had as I go through the process of adding every station available on the list of transmitters.


> On Sep 6, 2022, at 10:32 AM, tangerinesdr-request at lists.tapr.org wrote:
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> Today's Topics:
>   1. Compressed Spectrogram of VLF Spectrum (Jonathan)
> ----------------------------------------------------------------------
> Message: 1
> Date: Tue, 6 Sep 2022 11:31:35 -0400
> From: Jonathan <emuman100 at gmail.com>
> To: Unknown <hamsci at googlegroups.com>,  TangerineSDR Listserv
> 	<tangerinesdr at lists.tapr.org>
> Subject: [TangerineSDR] Compressed Spectrogram of VLF Spectrum
> Message-ID:
> 	<CAOY0kB24f-ks7n8kWZAGPmtNGiuRQQTaXkK-bUEt7aPTa9THiQ at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
> Hi All,
> Nathaniel was kind enough to let me use one of his older computers as a
> signal processing server and NAS for the recorded VLF signal from our VLF
> receiver and Raspberry Pi. I set it up to forward the timestamped 96k
> stream to the server via a network socket, just like the Whistler Catcher
> VLF module will do with the Tangerine SDR. I wrote a bash script to
> automate everything and it currently works as a systemd service for
> automatic startup. Here are a list of the programs running on the server:
>  15871  -  1.6  0.0 vtcat -B -L /data/log/vtcat_in.log ++9000 @timed,f4
>  15875  -  2.5  0.2 vtfilter -B -a th=5 @timed:1 @filtered
>  15879  -  9.9  0.2 vtresample -B -r192000 @timed:1 @timed192k
>  15884  -  0.7  0.0 vtcat -B @timed:1 -- -,f4
>  15886  -  0.2  0.0 vtwrite -B -L /data/log/vtwrite_96k.log -G 3600
> /data/vlf_96k
>  15890  -  4.2  0.0 vtresample -B -r32000 @filtered:1
>  15892  -  1.7  0.1 vtevent -B -d /data/events
>  15895  - 15.3  0.1 vtsid -B -c /home/user/sid.conf @timed:1
>  15898  -  3.1  0.2 vtsid -B -c /home/user/sid_resample192k.conf
> @timed192k:1
>  15901  -  2.2  0.1 vttoga -B -G 300 -i 25 -F 6000,16000 -d /data/togas
> @filtered
> As you can see, the SID monitor, vtsid, uses quite a bit of the CPU
> resources, but it's monitoring 17 frequencies for VLF transmitters as well
> as the mains fundamental, mains 3rd harmonic, the sferic band, and
> time-decimated spectrum data up to 16 kHz. I run a second instance of vtsid
> to monitor NAA. Due to the nyquist boundary being a multiple of 24 NAA's
> kHz, I need to resample the stream at a higher frequency to get proper
> absolute phase measurements.
> One of the really cool features of vtsid is that it can record
> time-decimated spectrum data along with amplitude and phase measurements of
> various signals. With this data, you can create a compressed spectrogram
> showing long durations of a day or more. Here is a compressed spectrogram
> of yesterday's UT day showing the daily sferic activity and the nighttime
> effect of the earth-ionosphere waveguide cutoff:
> [image: Screen Shot 2022-09-05 at 9.41.38 PM.png]
> I cannot tell you how unbelievably cool this visualization is!
> Jonathan
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