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Today I was trying to measure the SWR of a new aerial on my car which has 3 loading coils. Whilst doing this I took the whip out on the top to see how drastically I might have needed to cut the antenna and for reasons I can’t explain the SWR reading stayed the exact same.

I was using an analyzer going through the different bands just in case you were wondering.

Any idea on why this would occur? I’ve been licensed for 10 years and I just don’t know where to start.

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    $\begingroup$ What model antenna, what model SWR analyzer? $\endgroup$ – mike65535 Jun 10 '18 at 23:52
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If the SWR was very poor with the whip installed, you could simply be hitting the limits of your analyzer. Inexpensive analyzers are not very precise when the load is very poorly matched.

Alternately, something may be broken. Perhaps the analyzer, or the feedline you are using to connect it, the antenna mount, or the antenna itself.

I suggest testing each component individually.

Test the antenna analyzer with a dummy load. A dummy load should be a 1:1 SWR on every frequency. You can also try 25 ohms or 100 ohms and you should see a 2:1 SWR at every frequency.

Coax can be tested by putting a dummy load on one end, and the analyzer at the other: you should measure 1:1 at all frequencies. If jiggling the cable yields spikes in the reading, you have a poor connection somewhere.

Check for shorts with an ohmmeter in all your cables and the antenna mount.

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In addition to what Phil said, don't forget that a long (or just very lossy) feedline can mask problems by showing you a lower swr than if you would measure at the antenna directly. If the cable losses are high enough, your measurements at the end of the cable when you change things on the antenna side might not show you as much difference in swr as you would expect to see. If the cable isn't molded to the antenna, try to measure at the antenna directly. If it is, you might be able to short the antenna to ground and check if that has the expected measurement result.

Some (colinear) antennas might be shorted at the end by design, so if you would find it shorted at DC, don't jump to conclusions too quickly.

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