[TangerineSDR] TangerineSDR Digest, Vol 42, Issue 3

Wed Sep 7 08:14:00 EDT 2022

Hi Bob,

I have never used a SuperSID receiver before or the Windows or Python
software.

I use a Pi 3 with Audio Injector Stereo. My VLF receiver is an E-field
receiver based on an AD744 frontend. The antenna is copper tape attached to
a length of foam pipe insulation placed inside a PVC pipe. The receiver
also requires a good earth ground connection that is fairly well isolated
from mains hum sources.

I believe the SuperSID receiver circuit uses filters to pass the portion of
the band containing VLF transmitters. To test your SuperSID and antenna
placement, you can do the following:

Download vlfrx-tools source on your Pi, build it, and install it. Here is
the link <http://abelian.org/vlfrx-tools/> that includes install
documentation and dependencies.

With the SuperSID receiver connected to the left channel of the Audio
Injector and receiving a signal, run the following in a terminal window as
root:

vtcard -d hw:0,0 -b32 -r96000 -c2 -g-1 -v @raw

You should see it print messages. The first 4 would be "setup" messages,
then the rest should be "run" messages. Once it starts printing run
messages, it's capturing from the soundcard and outputting the stream to a
buffer called @raw.

In another terminal window under X windows or X forwarding, run the
following as any user:

vtspec @raw:1

This will show a live spectrum plot. Here is an example of mine showing
various peaks indicating VLF transmitters:

[image: Screen Shot 2022-08-01 at 10.29.59 PM.png]

You can then adjust the loop for the best signal and null out interference.

Here are some examples of my plots for 9/5 showing some SIDs on both NAA
and NML:

[image: Screen Shot 2022-09-05 at 9.28.15 PM.png]
[image: Screen Shot 2022-09-05 at 4.19.38 PM.png]

Because I use a GPS PPS with vlfrx-tools, it measures absolute phase as
seen in the sub plots.

Jonathan
KC3EEY

> On Sep 6, 2022, at 1:34 PM, Bob Stricklin via TangerineSDR <
tangerinesdr at lists.tapr.org> wrote:
>
> 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.
>
> Bob N5BRG
>
>
>
>
>
>> On Sep 6, 2022, at 10:32 AM, tangerinesdr-request at lists.tapr.org wrote:
>>
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>>
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>> than "Re: Contents of TangerineSDR digest..."
>>
>>
>> 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:
>>
>> PID RT %CPU %MEM COMMAND
>> 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
>> KC3EEY
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>> ------------------------------
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>> End of TangerineSDR Digest, Vol 42, Issue 3
>> *******************************************
>
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