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Thread: Using Analyser to build/test Antennas - please help

  1. #1

    Default Using Analyser to build/test Antennas - please help

    I have a N1201SA Antenna Analyser and have been experimenting with Antennas for 70cm/1090mhz adsb etc and to summarize...

    I seem to be getting odd effects from feedlines, so should I make a test length of coax and calibrate my analyser with the cable connected (no antenna) and use my calibration kit connected to the end of the cable so that I am only reading the Antenna in question? A Dummy load directly connected to the analyser reads correctly but put it on the end of a patch lead etc the readings are (to me!) incomprehensible.

    I am making Yagis where the driven element is a dipole (not folded) where the impedance I would expect at resonance to be 70-75ohms? How does using either 75 ohm low loss Sat cable (NX100 for 1090mhz) or 50 ohm rg8 etc affect my analyser readings when the analyser is expecting 50 ohms and the dipole or sat cable is 75 ohms?

    Where one cannot get to the antenna (i.e. when it is up a tower!) what use is checking with the analyser? or do we accept that the cable is part of the antenna system?

    Any help very much appreciated.

  2. #2
    Super Moderator pmh's Avatar
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    My analyser requires specific range of resistances to be connected as it runs through the calibration process. These are connected directly to the analyser.

    The feeder is very much part of the system. Why would you want to take readings without it? Also, your analyser shouldn’t be expecting a specific impedance, but report what it actually sees.

    Kind regards,



    Phil

  3. #3

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    (hopefully my pictures are showing on this thread...)

    1st photo shows analyser connected to 50ohm calibration source with trace from 137.5mhz to 2.7ghz - a flat trace of 50ohms impedance right across the screen...

    Second photo shows 50ohm calibration source connected with coax and the trace is all over the place -

    The manual for my analyser hints at using the calibration kit on the end of the coax to null out its influence but its wrote in chinglish so not easy to comprehend.

    Some suggestions to cutting the coax to some multiple of a wavelength.... an esoteric process that relies more on the phase of the moon and high/low tides than to any science -

    Why the eratic trace?

    https://www.dropbox.com/s/59tu5r7j5387hbw/1.JPG?dl=0
    https://www.dropbox.com/s/784fkiygqmoim3c/2.JPG?dl=0
    Last edited by blake; Thu 28th Jun 2018 at 10:10. Reason: trying to upload a photo

  4. #4

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    Like Blake said, in read mode the analyzer just reports what it sees. Using the cal kit on the far end of the coax should normalize the cable as part of the system,
    Analyzers only check problems up the tower. The antenna is usually good to go when installed I would hope.

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