MDX Transmit Issue

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MDX Transmit Issue

Post by Prospect62 » Sat Mar 10, 2007 10:50 pm

Anyone ever hear of a problem with MDX's losing output power when they get warm? My VHF MDX seems to work ok when physically cold (it's an avg of 25 degrees around here this time of year). Then, after riding around in my hot truck for awhile it won't hit my county's emergency communications repeaters. It seems like it is losing power or the frequency is shifting or something is going on.

Any insight into this problem would be great. Thanks!

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Post by Meatball » Fri Mar 16, 2007 8:23 pm

I can't really recall anything specific with the MDX. However, I've seen plenty of mobile radios that have had temperature related issues. All modern MACOM mobiles have an RF hybrid module, either as the final power amplifier or driving a pair of RF transistors. These seem to suffer from intermittent issues where the leads are ultrasonically welded to the substrate.

If you don't have a wattmeter, you can use ammeter to see if the final is still drawing current when it gets warm. A 25W radio usually draws about 7 amps and a 45 watt radio around 10 or 11 amps when it's putting out full power.

Your best bet would be to see if you could borrow a wattmeter, a dummy load, and a can of freeze spray. Wait until the thing warms up and loses power, then hit the power module and surrounding components with freeze spray.

Make sure the radio isn't right in front of a heater outlet. I do recall a plow-truck where the owner had installed the mobile radio right in front of the vent. Of course, after riding around for hours plowing, the poor radio was cooking and if I remember right it just stopped putting out power.

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Post by Prospect63 » Tue Apr 24, 2007 10:51 am

Thank you Meatball. I've come to the conclusion that the radio has been toasted. I do have it mounted right in front of my floor heating duct on the hump. As of right now, it's just not putting anything out. I purchased a used KMC to replace the MDX for now. Just need to update my ProGrammer revision now :( Anyone looking for a cheap used MDX?

By the way, there were some discrepancies with this stupid board so I had to re-register as Prospect63 instead of Prospect62. FYI.
I used to be Prospect62

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