A very easy way to tune stubs is with the AEA 121 or CIA. Using a Tee
connector on the top, with 50 ohm resistor or a low power dummy load plugged
into one side and the stub plugged into the other side (i.e. in parallel),
trim the stub for minimum SWR at the frequency you are interested in (if you
are doing a 1/4 wave stub, do it at 2x the frequency). Adjust the sweep
bandwidth on the analyzer as needed to get the resolution you need. You can
easily tune a length of coax within a few kHz.
I do this all the time for stubs, coax lengths for phasing, etc.
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