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Author Topic: Diamond SG7500A  (Read 845 times)
K9BDG
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Posts: 3




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« on: October 21, 2008, 10:54:30 PM »

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.
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WA7NCL
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Posts: 625




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« Reply #1 on: October 22, 2008, 08:49:42 AM »

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.
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W3LK
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Posts: 5644




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« Reply #2 on: October 22, 2008, 11:36:07 AM »

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

73,

Lon - W3LK
Naugatuck, Connecticut
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
K9BDG
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Posts: 3




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« Reply #3 on: October 23, 2008, 07:11:24 PM »

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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