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Question about application for GHz dual-channel downconversion receiver for GHz VNA #1112
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I think the trickiest part would be locking the frequency to the 10 MHz reference. Why (re)start from the SDR receiver if there is already a working VNA in this repository? It already has two synchronous SDR receivers and a Python code example. |
Excellent question! I did not realise the current 50 MHz VNA had two receivers! That is totally 100% the place to start then. Thanks!
I guess since I will not be using the RP outputs on my VNA, I could use one of the RP outputs to output a 10 MHz reference and use the generator in external REF mode, that would probably work, I'll dig into the code as soon as I have some free time Cheers, |
If you do not use the outputs, then I think that you do not need additional frequency synchronization. I think that the phase difference between IN1 and IN2 signals does not depend on the parameters of the local oscillator used for mixing inside the SDR block on your diagram. |
Agree, as long as only a single LO is used in the SDR block for both inputs, then we should be good! I am looking forward to building it and trying it :) |
Description of the setup:
Description of the problem:
I'm looking into implementing a GHz VNA using a red pitaya as the IF digitizer / demodulator to replace the commercial GHz VNAs (eg. PNA5222A) we have in the lab.
I've been looking around and think that the SDR receiver could be a great building block for this, but then with two channels that share a common single digital IQ demodulation reference to achieve phase alignment. Here is a block diagram with my full idea:
I'd like to stream the IQ data from the RP straight into python where I can further decimate / filter (if needed) to increase SNR (we often use a 1 Hz IFBW in our data acquisition...). We need the two channels to calibrate out the non-flatness of the generator power vs freq, and also to measure the randomized phase alignment we get on the two MW generator channels whenever a frequency is changed, along with calibrating and correcting for imperfections in the downconversion mixers.
(for RF nerds: The down conversion is vulnerable to image leakage, but that is not a problem in principle since only one frequency is coming in on their RF ports...this is also how our expensive commercial VNAs are implemented...)
I guess my question is if there is a possibility to implement this idea using the code in this repo, or maybe with some modifications?
My requirements are:
And some things that would be nice would be, on the longer term, could be:
I'd be very interested to hear what you think, and can also donate my own time (limited) and perhaps also time of a university programmer to help
Thanks in advance!
Gary
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