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1. 12:49 PM - Re: King KX155 weak VOR reception (David Josephson)
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| Subject: | Re: King KX155 weak VOR reception |
On 7/14/14 11:59 PM, Avionics-List Digest Server wrote:
>
> Re my interest in an antenna analyzer: I've been looking at some of
> the newer units online (such as the Rigexpert AA-600) and it appears
> they have the capability of testing the coax for faults (distance to
> fault) while connected to the antenna. I wasn't thinking of
> replacing the RG58 with RG400 simply because of the RG400 is a lower
> loss cable, rather I wanted to use the analyzer to check the RG58
> for faults. I would replace the RG58 with RG400 ONLY IF the RG58
> is questionable (open, shorted, etc). This BTW may be a real
> possibility because the existing cable makes some pretty tight bends
> under the panel. Also using a tester such as the AA-600 would
> allow me to check the SWR of the antenna.
>
> Thoughts?
My thoughts are that you really want to buy a new antenna analyzer.
Great, but only if you're willing to invest in the time needed to
understand what's going on. These things are not magic and can easily
produce numbers and graphs that can fool you if you don't know what
you're looking at. You do have the ability to make an S-parameter
measurement over a range of frequencies, and remote it to the end of a
characterized transmission line by the use of time gating so you can
actually measure the antenna separately from the coax -- this is a
powerful tool. Just prepare for a steep learning curve.
I don't know about the AA-600 specifically, I have always done this with
traditional lab equipment. I would suggest looking at the VNWA 3E
(sdr-kits.net) as an alternative to the AA-600. It's about the same
price, uses a PC for display, works up through DME/ATCRBS frequencies,
and is supported by lots of hams worldwide who use it for antenna
development.
Finally, no amount of electrical sleuthing will tell you whether the
antenna was an effective receive device as built. It may have a good 50
ohm match which is nearly irrelevant to its performance as a VOR/LOC/GS
antenna.
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