UHF Signal Dropping

SRFlanigan

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Joined
Sep 11, 2019
Messages
6
I seem to be having an issue with incoming signals on a UHF frequency dropping and then returning. The signal is not fading, just dropping entirely for a word or two and then comes back strong only to drop again for a few words and then returning. The repeater I am connecting to is ~25 miles away, however, when I request a signal check, I am told that my signal is strong and clear with no audio drop-outs from my side. As a side-note, I am not having any of these issues on any VHF frequency I operate. Strangely, this "dropping out" does not happen on my HT on the same frequency. In fact, I have had my HT, (an Anytone 878UV) sitting in the seat next to me, and while both radios are on the same UHF frequency, the HT signal doesn't drop, but the mobile unit, an Anytone AT-578UV Pro does. (I hope it's not the radio.)

My mobile antenna is a Diamond NR770HNMOB. I had to run a coax extension to make it from my trunk lip-mount NMO mount to the front of the car. I put the antenna on an analyzer and found that my SWR is 1:1 on the UHF, (and VHF) frequencies I run. I checked the antenna and mount for any signs of corrosion but, outside of some normal "dirt", found none. I cleaned both the antenna and mount contacts and remounted the antenna, checked the antenna on the analyzer again, and once again my SWR readings are 1:1.

I am starting to feel that it might be the antenna itself. I thought Diamond had a fairly good reputation, but have been reading of late that other users have been having issues with this model as well. So, I am looking for other's inputs as to what may be causing this issue. Also, I am open to suggestions about other antennas that might perform better. I am trying to stay away from the "fold-over" models, but if this is what it takes, I might just concede defeat and purchase one, providing it has the NMO mount. I do own another Diamond, a CR8900A Tri-Band antenna, (fold-over,) but feel that it would be overkill for a dual band radio, plus I would have to change my trunk mount as well.
 
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SRFlanigan

Member
Joined
Sep 11, 2019
Messages
6
Have you ruled out a priority scan setting? Usually that is the cause when someone complains of drop outs like that. If the drop out is precisely timed, then that would reinforce that.
Yes. Actually this is the first thing I thought about, but have ruled this out as scan is not activated.
 

mmckenna

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Yes. Actually this is the first thing I thought about, but have ruled this out as scan is not activated.
OK, can you try swapping radios? If you have an adapter, connect the portable radio to the mobile antenna and see if it carries over. While it may be the antenna, it can also be noise sources in the vehicle.

As for the antenna, make sure everything is tight and start checking for continuity with a multimeter.
 

FKimble

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Jul 14, 2014
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Newnan, GA
Do you have weather alert, or what ever it's called on your radio, enabled? If so turn it off.

Frank KK4YTM
 

SRFlanigan

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Joined
Sep 11, 2019
Messages
6
OK, can you try swapping radios? If you have an adapter, connect the portable radio to the mobile antenna and see if it carries over. While it may be the antenna, it can also be noise sources in the vehicle.

As for the antenna, make sure everything is tight and start checking for continuity with a multimeter.
I haven't tried swapping radios yet. I put the antenna on an analyzer; looks good. Haven't tried a continuity test yet though.
 

SRFlanigan

Member
Joined
Sep 11, 2019
Messages
6
You have another antenna, check if you get the same results with the other antenna.
Actually I did. I just swapped out the Diamond and it's NMO trunk mount with a Larsen and a Larsen NMO trunk mount. This particular frequency is still breaking up.
 
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