Help with troubleshooting.

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Mar 15, 2017
Hi all!

I am using a Kenwood TM-281 (modified to transmit in commercial range, tut tut tut I know) and am having some what seems to be interference issues. It seems to be worse at certain frequencies but when I transmit, my Nav/entertainment screen gets brighter. Also, due to work requirements, I have an external Garmin Nav system with GPS GeoTrac installed also and the screen on it does the same, and from time to time will actually power down and restart. I have also noticed my receive signal isn't all that great, although I am told my transmit signal is loud and clear. I have a TM-271 set up the same and had the exact same issues. Not too sure on my antenna type but its a left fender mount setup. I bought it from a reputable radio comm shop so the antenna type should not be the issue as they know I wanted it for commercial use. Do these antenna mounts need to have a really good ground? It is currently mounted to the left fender under the hood to the body over painted metal using just self tap screws. Should I sand off an area under the mount/screws to get a better ground to the mount? I have a couple friends with the exact same setups on similar trucks but I seem to be the only one having issues where they can hear me transmit no problem but I cannot hear them and someone next to me can hear them loud and clear. Help would be greatly appreciated!!!


Nov 18, 2008
Campbell County, Wyoming
Sounds to me like RFI. First item I would check would be antenna (including the coax and SWR). The next thing would be to check the filter on the radio-just because the processor will key the transmitter by no means means all is well. The matching network built into the radio was designed as a low pass filter for the amateur band and may be doing all kinds of things to a signal outside of its design pass band. Due to the fact you are having issues on receive also, my first guess would be antenna related (High SWR works 'both' ways). Hook up an antenna analyzer and check the coax and antenna at the operating frequency. Next step is using a dummy load and see how the radio actually works at the operating frequency. Amateur radios used of of band with out checking everything out can cause the radio to go up in smoke.

BTW another item is that ham gear is usually what is now known as 'wide FM' and VHF business and Public Service now use 'narrow band' -most ham rigs would receive the signal but the audio would be considerably lower and units receiving the radio would likely notice loud or bad audio compared with other users.

As you already know about the legal issues, I will keep it simple and say that the radios are built to follow the rules and not following the rules has consequences over and above the ones you think of like 'being caught'.

There are low cost two way radios designed for part 90 that meet the spec and work better than your Kenwood because they were designed to do so.

take care
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