[TangerineSDR] VLF Audio Interface for Tangerine SDR

[Tom McDermott]

Hi Jonathan,  this looks like a good addition to the receivers available
for TangerineSDR.
The CS5364 IC has some nice specifications, and the ability to receive an
external clock,
so it looks like a good potential choice.

I notice that the frequency selectable input range is interesting (I've not
seen a similar mode
selection of operation on other components):
* 2 khz - 54 khz  or
* 54 kHz - 108 kHz  or
* 108 kHz - 216 kHz

-- Tom, N5EG


On Sun, Jul 12, 2020 at 10:14 PM Jonathan via TangerineSDR <
tangerinesdr at lists.tapr.org> wrote:

> Hello,
>
> For those who don't know me, I'm Jonathan, KC3EEY, a natural radio VLF
> enthusiast. I'm also a senior EE student at the University of Scranton
> with Nathaniel, W2NAF. When Nathaniel and I first met, we both
> discussed our projects, interests, and work. He talked about the
> possibility of adding VLF capability to the PSWS and since then I was
> always thinking about how to implement it.
>
> VLF receivers are often homebrew and consist of an input stage
> interfacing an H-field loop or E-field probe to a gain or driver stage
> with the end result an audio output. It's convenient that  most of the
> VLF band is within the audio range which means no downconversion is
> needed and can be recorded directly as audio. Some examples of E-Field
> receivers are Steve McGreevy's WR-3 and BBB-4, as well as the NASA
> Project INSPIRE VLF3 receiver. Most of these receivers are intended
> for portable use but can be used in permanent installations. For the
> PSWS, VLF receivers will be used in a permanent installation, like the
> HF antenna. The intended setup for this purpose will consist of an
> E-field receiver and two H-field receivers with orthogonal loops for
> triple axial reception. This allows for distance and bearing
> calculations of VLF signals.
>
> The VLF receivers will be setup in a location with minimal power line
> interference so as not to overload the input or gain stage of the
> receiver. Rural areas are ideal locations, but sometimes suburban
> locations can be suitable. The receivers can be powered by batteries
> or through isolating DC-DC converters operating at a high switching
> frequency above VLF. The audio output from the receivers must also
> have an audio isolation transformer on  the audio output on the
> receiver. The audio (and sometimes power) is fed through a feedline of
> cat5/6 cable or coax, and on the other end it connects to the
> soundcard of a computer for audio capture. An audio isolution
> transformer is also needed on the soundcard end as well (and an
> isolating DC-DC converter if powered by the feedline). The reason
> isolation is required is because power line interference can be
> coupled into the receiver, often through earth and chassis grounds
> like the chassis of a computer.
>
> For the Tangerine SDR, I wanted to offer to design a plug in module
> for one of the interfaces on the data engine. A soundcard is often an
> ideal SDR for VLF, so I had a "soundcard interface" module in mind. I
> wanted 192 kHz sampling with 16-bit samples and a high dynamic range,
> at least 100 dB. After some research, I decoded to use the CS5364
> 4-channel audio analog to digital converter. Digital audio output is
> accomplished with TDM or I2S which is clocked into the FPGA of the
> data engine. From there, the samples are GNSS time-stamped and made
> available via a TCP socket over the ethernet port.
>
> As discussed with Tom and Scotty in the Tangerine SDR Zoom, the GPSDO
> will provide the A/D master clock and time-stamping will be done in
> the FPGA. The CS5364 has both hardware and software configuration mode
> and looks fairly easy to use. I plan on looking into the evaluation
> board and starting the design of the input stages. This is a little
> new to me, but I have dabbled in digital audio in the past,
> specifically with Cirrus Logic audio ICs. I plan on laying out the
> board in Kicad. Details on the timestamping, possibility of hardware
> or software control, and network availability will come soon.
>
> Thanks again.
>
> Jonathan
> KC3EEY
>
> --
> TangerineSDR mailing list
> TangerineSDR at lists.tapr.org
> http://lists.tapr.org/mailman/listinfo/tangerinesdr_lists.tapr.org
>
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