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Null in IQ spectrum

LA3PNA
LA3PNA Member, Unconfirmed ✭
in SmartSDR API
Hi.
I'm trying to pipe the output of the DAX IQ stream into a python script into a python script. Reading the data from the sound device with sounddevice.InputStream on DAX IQ RX 1 @ 96,000 Hz, 2 channels, float32, I get a spectrum, but there is a null in the stream around the center frequency on the waterfall.
This gives a 16KHz dead band in the center of the spectrum where there is no data.
Image: https://imgur.com/a/QqwBhKl

In windows sound, DAX IQ RX 1 is set up to 2 ch, 24 bit 96KHz studio quality for the input settings.

If I do a complex frequency shift, the null does move, so it looks like it is in the input data and not in my program. Testing with a synthesized IQ data file, I get full spectrum.
This is only tested with my FLEX-6300, but I will test with my 6600 this evening.


Any pointers at all to if this is expected behaviour or if there is something I'm missing would be appreciated.
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Answers

  • K1FR
    K1FR Member ✭✭

    OM:

    I am far from expert on this. However, a few years ago I was working on something similar. I am assuming you are using the UDP stream? One suggestion is to look at the past posts on this Flex site about the UDP data stream. There is some good stuff from the Flex engineers that wrote a lot of their software. Look up the VITA-49 protocol documents - it took me a long time looking at the stream with WireShark before I was interpreting the UDP VITa-49 stream correctly.

    I ended up changing to using the IQ stream available via the Windows Sound System (WSS). That is 48K complex samples per second which was good enough for what I was doing. It worked well to record the I/Q stream using sounddevice.rec() function.

    Good luck! Your post got me interested in going back and finishing the project. Just looked up the Python code - now to try to figure out what I was really doing again. 😁

    73, Tom

    K1FR

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