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) >I'm not that familiar with the Flex hardware, but it certainly seems >that this could be used to provide both generator and detector since >it's full duplex, allowing both reflection and transmission >measurements with appropriate pads, bridge, etc. I think you'd also need some relays to switch the source and receiver ports. Essentially, what you'd need is similar to the "S-parameter test set" on an older HP VNA (like an 8510). Do it right, and you could also build the equivalent of the new Agilent E-Cal boxes. With these, the characteristics of the loads, shorts, opens, and thrus are all stored in the ecal box (after having been measured on a "golden VNA"), and the VNA calibration algorithm uses that data. For what it's worth, the modern trend is to do less with Shorts and Opens, and, instead, use multiple Thrus and precision mismatched loads. Partly it's because it's hard to make a precision open, and also because it lends itself better to testing multiport networks. The advantage to a short or open is that it makes the math easy, which is important if you're doing the cal by hand on paper. If you're doing computerized cal (which everyone does, these days), there's no particular advantage in a short or open, especially if you have to deal with non-ideal shorts and opens anyway. It's very easy to make precision air line, for instance, that has very well controlled characteristics determined entirely by mechanical construction tolerances. That's a heck of a lot easier than trying to find low inductance resistors and carefully arrange them around a connector to get something that is uniformly flat. Jim, W6RMK James Lux, P.E. Spacecraft Radio Frequency Subsystems Group Flight Communications Systems Section Jet Propulsion Laboratory, Mail Stop 161-213 4800 Oak Grove Drive Pasadena CA 91109 tel: (818)354-2075 fax: (818)393-6875 -------------- next part -------------- An HTML attachment was scrubbed... URL: http://mail.flex-radio.biz/pipermail/flexradio_flex-radio.biz/attachments/20070628/29c7e28a/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/
