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VHF Network Analyzer

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G8CIX View Drop Down
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    Posted: 13/January/2017 at 14:22
HI

Looking for a network analyzer to align some duplexers. Wondering if there are any PC based options or if it can be done using an MFJ swr analyzer.
Martin G8CIX

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G1HUL View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote G1HUL Quote  Post ReplyReply Direct Link To This Post Posted: 13/January/2017 at 18:09
At the very least you need a spectrum analyser and linear noise source / sweep generator.

There has been some experimentation with the AirSpy SDR receiver using the cheap noise sources from eBay, with good results but as always limited by the dynamic range of the receiver (AirSpy is good to about -80dBm and reasonably linear, so feasible for commercial 3-pot duplexers). Info on the AirSpy Yahoo group.

IIRC there is a PC-based network analyser out there, can't remember the details.

Other than that, the Rigol or Siglent entry-level spectrum analysers will easily do the job (plus you get a good analyser into the bargain!) but you are talking £1500.

Using an MFJ is not feasible as it doesn't show loss through a feed line, plus the tuning is very course when compared with that needed for cavities.
Jim, G1HUL
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If everyone is thinking alike, then somebody isn't thinking.
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G0DUB View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote G0DUB Quote  Post ReplyReply Direct Link To This Post Posted: 17/January/2017 at 20:58
Hi,
emphasising that I haven't tried this personally ( though all I need is patience and a very rainy day ) there is something I read about called 'Dishal's method' for aligning multi-resonator filters.
A reasonable description is on page 8 of Scatterpoint at this location
http://www.microwavers.org/scatterpoint/2012/Scatterpoint_1201.pdf

It was also mentioned in either an old RSGB VHF/UHF manual or Microwave Handbook but I haven't got those off the shelf yet.

Greg, G0DUB

West Cheshire RAYNET Group Controller
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