Hello! Most of the time I do not anything of significance to contribute, but VNA's are near & dear to me. I currently have a grad student working on a poor mans VNA that will go to 2700 MHz. The issue is phase measurement over that range, which, even though there are a bunch of chips that purport to do this, not really. So a synthesized tracking dual channel super het system is needed to measure phase over 0-360 degrees, where the phase component of the vector is measured at a fixed frequency, comparing the reference to the test channel. A good starting place for understanding is the manual for the HP8410A/B/C VNA from the '80's, available online at Agilent. It will explain many of the issue and provide a block diagram that you can modify with modern components. Two synthesizers (or a dual with IF offset on one) are probably the best way for the stimulus & receiver LO. 73 Jeff Kruth WA3ZKR In a message dated 6/2/2014 12:00:28 P.M. Eastern Daylight Time, [email protected] writes:
Message: 1 Date: Mon, 2 Jun 2014 16:43:12 +0200 From: Attila Kinali <[email protected]> To: [email protected] Subject: [time-nuts] VNA design Message-ID: <[email protected]> Content-Type: text/plain; charset=US-ASCII Hi, I know this is not exactly a time-nut question, but i guess this is the best place i know to ask about this stuff. I recently got introduced into the usefullness of a VNA. But these things are horribly expensive for home use, even if bought from ebay (before you say anything, remember i live in europe, where every boat anchor hast to travel a long way). But given that most of the designs that are on ebay are from the 80s and early 90s, i thought that with todays ICs it should be easy to come up with a design that does the same thing but can be build on a kitchen table. Well, my problem now is, that i don't know how to build a VNA. Yes, i understand the basic principle. I can come up with a design that should work. But i have no clue about any problems or difficulties in building these devices. Ie it's very likely that i fall into a dozen traps when i try to build one. I tried to get information on how to build a VNA, or what kind of trouble people had operating one, but beside the VNA book[1] Rick mentioned a couple of months ago and ko4bb's site (thanks man! your manual collection is a gold mine!), my searches came out blank. As i'm quite sure that there is information of that kind out there, i would like to ask whether someone could point me to some documents, webpages, books, papers, etc that would show me the detailed design of VNA, the problems people had with some designs or anything else that would be of interest in such an endavor. Also, any good resource on how to build a directional coupler that does 10-3000MHz without going to exotic materials would be much appreciated. All papers i found deal mostly with stuff above 5GHz. Seems like "low frequency" couplers are considered "a solved problem". Attila Kinali [1] Handbook of Microwave Component Measurements: with Advanced VNA Techniques by Dunsmore, 2012 _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
