Can an SDR simultaneously broadcast on multiple frequencies?

Discussion in 'Software Defined Radio (SDR)' started by VU2TVE, Oct 16, 2019.

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  1. KA9JLM

    KA9JLM Ham Member QRZ Page

    I have a NUC and Run Linux on it.

    The CPU is fast, But I am not sure about graphic speed for something that requires a lot of graphics power. It would rate fair.

    I really like that little computer. :)
  2. VU2TVE

    VU2TVE Ham Member QRZ Page

    Ordered a HackRF One today. Can't wait to see what it does :)
  3. VU2TVE

    VU2TVE Ham Member QRZ Page

  4. VU2TVE

    VU2TVE Ham Member QRZ Page

    @W6RZ, So, I was able to transmit up to seven FM signals with the HackRF one connected to a 2W linear amplifier, and things generally seemed to work well. I will go into details in a future post, but as a proof of concept, it seems to work! So thanks a lot for your advise.

    Going beyond seven maxxes out my 5 year old laptop CPU, but that's not an issue, as I can purchase a much more powerful CPU and try on that.

    I noticed that GRC has a UDP source and sink block, so it might be theoretically possible to generate signals on one machine, and send them to another machine over LAN which is hooked upto the SDR to spread the processing needed. Do you think I might run into timing or other unforeseen issues with that?
  5. VU2TVE

    VU2TVE Ham Member QRZ Page

    This is the current setup
  6. KV6O

    KV6O Ham Member QRZ Page

    What band are you transmitting 7 signals on? What are you transmitting? What's the legality of this? Broadcasting is illegal on ham bands.

    Cool in concept, but into a dummy load and no PA required unless you can show an legal ham application - I can't think of one. But I could very well be wrong!
    K3XR likes this.
  7. W6RZ

    W6RZ Premium Subscriber QRZ Page

    The UDP blocks should work fine. The timing issue you need to look out for is the "two clock" problem. Since you'll be taking microphone input, there will be a slight mismatch between the SDR sample rate clock (divided down to 48 kHz) and the audio capture clock. If the audio clock is faster than the SDR clock, you'll eventually build up samples and it will cause an increase in the latency. If the audio clock is slower than the SDR clock, then you'll underflow samples and it may cause glitches in the audio.

    It may or may not affect you too much. It will depend on the exact mismatch and how long you operate the system. If it's just a few hours at a time, you may be able to get away without any compensation.

    The solution is to use a fractional resampler in each audio path and control the resampling ratio with some sort of buffer level or latency indication. Here's a video that describes how to control latency in general (which can be applied to the two clock problem).

  8. VE7BPB

    VE7BPB Ham Member QRZ Page

    Ah, yes. The Radio Police stumbles into the room, blind and drunk, and proceeds to chastise the filthy miscreant. Never bothering to read the thread before virtue signaling his noble opinions for all to see.

    And laugh at...

    regards, Roy
  9. KV6O

    KV6O Ham Member QRZ Page

    Laugh away. It was kindly explained to me via a PM. They ARE valid questions, and I DID say, "I could very well be wrong", no?

    But whatever makes you laugh. :rolleyes:
    WR2E likes this.
  10. WR2E

    WR2E Ham Member QRZ Page

    Will I be 'chastised' also if I ask;

    Why would someone want (or need?) to transmit multiple 'broadcasts'?

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