Lately I have been wondering if anyone has worked toward making several #NooElec NESDRs phase-coherent?
If one of you knows of such an attempt, can you point me to them please?
[#]hamradio #sdr
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@AG7GM not familiar with the hardware, but they appear to use the same chip as any RTL-SDR DVB-T dongle and there's plenty of those being used coherently.
Essentially, get a clock, 10 MHz if I recall, distribute it to each unit. Job done.
Example: https://www.rtl-sdr.com/a-multi-channel-coherent-rtl-sdr-product-for-passive-radardirection-finding-and-more/
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@vk6flab Thank you, Onno. I have some reading to do!
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@vk6flab @AG7GM It's not that easy, I'm afraid. While it's trivial to get the RTL2832 sample-synchronous by feeding them the same 28.8MHz clock, the tuner chips have individual PLLs that will lock differently. So you will get different phase shifts between channels every time.
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@hennichodernich @vk6flab Hi Paul. I appreciate your insight. I have very little experience with understanding such things. Yet.
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@AG7GM
That's what the KrakenSDR is
https://www.krakenrf.com/product-page/krakensdr
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@abortretryfail Yaaas. That's a great tool to locate a transmitter. I was curious about using the phase coherence to cancel noise.
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@AG7GM
I've read an account by someone working on something like this recently, but I can't find it. (I assume a random old QEX back issue.)
The article was about TOA-based transmitter discovery within a city with SDR sensors spread around the city, but it's the same underlying problem: there was no way to feed a coherent clock to scattered receivers, so post-processing was required.
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@AG7GM
The approach taken was to tune oscillators precisely (using some synchronising signal from phone towers!), then listen to a single-location broadcast transmitter immediately before/after each location attempt and then correlate. Once the correct offset for the broadcast station is calculated, it's reasonable to use it for the rest of the calculation on the basis that drift is unlikely to be a problem over the several seconds of the location attempt.
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@AG7GM
In your case, you'll use a single external oscillator to achieve identical tuning, but still need to correct for phase errors introduced by the uncorrelated action of the per-radio PLLs. So long as the time between correlating with a reliably stationary external source and whatever you're relying on phase-coherence for is reasonably short, you should get a workable result.
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@9v1rt I follow the thinking, but my electronics knowledge has about an inch of dust on it. I'll need to totally study up on it to jimmy something together.
That said, if someone has already done it, I'm enough of a monkey with a soldering rig and a microscope to copy someone's work. :D
I'll need to scope the QEX stuff.
Thanks dude.
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@AG7GM
Found it:
TDOA System for Transmitter Localization
Stefan Scholl, DC9ST
QEX May/June 2019
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@9v1rt Dude! You rock! \m/
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