Diamond SG7500A

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Andries Engelbrecht:
I got a a Diamond SG7500A antenna to use on my truck fro 2M/440. When I tested the installation it showed a short on my multimeter, yet it seems to work OK. Is it normal for these antennas to show a short with a multimeter?

I also tested the same mounting locations with a Comet SBB-5 and it showed an open circuit. So the DC short is definitely in the SG7500.

I realize that RF impedance is very different from DC resistance, but I normally just do a simple basic check with a multimeter to make sure the cable or mount didn't get damaged.

Bill Burrows:
Maybe.  Its theoretically possible to have an antenna that is an RF radiator be a DC short.  A half wave end fed with a tapped LC to ground would be a DC short when measured at the feed point.

You need to know what kind of antenna you have.

SWR or FWD vs Reflect power should also give you a good idea of whether it is installed properly.

Lon Kinley:
Many antennas show a DC short across the feed. This is normal.

73,

Lon - W3LK
Naugatuck, Connecticut

Andries Engelbrecht:
Thanks for the info. Just needed to verify.

Either way I measured the antenna tonight and it doesn't show a DC short anymore, so maybe I just messed up when I initially measured.

The SWR seems to be pretty good when mounted to the hatch, lower than 1.5 on both 2m and 440 across both TX spectrums.

73
Andries

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