At 07:23 PM 6/28/2007, Larry Phipps wrote: >Comments in context below. > >Jim Lux wrote: >>At 09:41 AM 6/28/2007, Larry Phipps wrote: >>>Thanks for the plug, Army. I think Jim had something else in mind, >>>and I may be able to shed some light on the discussion. Paul >>>Kiciak, N2PK, who developed the very accurate N2PK VNA has been >>>playing with the concept of an SDR VNA. He has posted this >>>tutorial on using the Softrock40 with Rocky 3.3 software to do >>>very accurate reflection measurements on the cheap. >>> >>><http://www.dxatlas.com/Rocky/Rocky_VNA_v1c.pdf>http://www.dxatlas.com/Rocky/Rocky_VNA_v1c.pdf >> >> >>Is Rocky open source? >>I know Paul worked with Alex to implement the calibration >>algorithms, but those algorithms aren't published, are they? Maybe >>Paul has published them somewhere else.. >> >>Most of the software I've seen for the N2PK VNA is executable only. >> >>that would make it somewhat of a challenge to integrate into >>PowerSDR (or, for that matter, to modify it to work with a >>Flex-Radio based widget instead of a N2PK) > >The N2PK hardware has nothing to do with this. Paul and Alex have >come up with something that uses the Softrock40 as the hardware.
Good point.. but, still, if Rocky is closed source, and there's no open source version of Paul's algorithms, then we'll need to get Paul psyched up to help with the work for the Flex platform. Should be similar, at least, to the SoftRock. And before someone leaps on me about this.. yes, VNA calibration algorithms, in general, are published.. but the practical implementation details are not. It's sort of like having a copy of Oppenheim and Schaefer has all the DSP algorithms in it, but is a long way from a practical implementation. >No relays are involved. The TX and RX are simultaneous. You do need >to add a few 2N7000s to allow switching the Softrock40 between >normal and VNA modes. The relays are needed so you can do a full two port measurement. I would think you need to measure the device under test's S22, so you can remove that contribution from the "receive" side measurements. Speaking here of measuring two port devices, as opposed to a straight reflectometer measuring a 1 port device. >FWIW, because my LP-100 does its VNA thing at high power (up to >1500W), I don't use O/S/L techniques for calibration, but rather >some known bracketed loads for calibration. Exactly what the modern PNAs do. > The LP-100 is a digital wattmeter with vector impedance > capability, but because of that I am able to extend it's > capabilities into the VNA realm. It is not as accurate as a N2PK > because it is based on an AD8302 gain/phase chip, but it has the > advantage of being able to be used in any RF environment since the > source power can be as high as needed to swamp nearby broadcast stations, etc. That is a HUGE advantage, by the way. > My software is free, but not open source. And that appears to be the case for most (if not all) low cost VNA solutions. I've got some software that's open source (or it will be, as soon as it finishes wending its way through JPL's software release process) to do parts of the job. And, I'd be willing to work on extending it. Jim, W6RMK -------------- next part -------------- An HTML attachment was scrubbed... URL: http://mail.flex-radio.biz/pipermail/flexradio_flex-radio.biz/attachments/20070629/a65aa9e7/attachment.html _______________________________________________ FlexRadio mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: http://www.flex-radio.com/
