MXt-575 Squelch Issue

[WSBU859]

The Radio having an issue is a MXT575. Installed in a 2002 F250 that has an aftermarket radio a JVC Kw-M56 ( basic touch screen stereo back up w/camera) all else is stock.

The Radio is installed with a direct connection to the battery through on 14 gauge copper wire w/ fuses and relayed disconnect.  The Antenna is the magnetic mount unit that came with the radio. The Coax is routed from the cab to the roof via the passenger side rear cab door seal. The antenna is  affixed to the center of the roof.

The issue: I am having is intermittently when the radio is turned on it will immediately experience a squelch break. I have experienced this at maximum squelch (9). 

I have checked the antenna SWR across the GMRS band at mid band the SWR is 1.86 the the top of the band the SWR drops to 1.67 the bottom is similar. Input voltage is 12V engine off and 14.1 with engine running. I own and carry from time to time two 2m/70CM Yaesu/Baofeng handhelds and a GMRS hand held Baofeng. Midland suggested they may be the cause. The interesting thing is it happens when they are off or not in car. More interestingly when the are on none of these radios experience a squelch break.  

It sounds like the radio has a defect. Strangely I took the radio into the house and powered it off my station 30A power supply and cannot get it to duplicate the issue. I put the antenna on a large steel locker for a ground plane and tested the SWR , it is below 2.0(see numbers above.) 

  I am concerned that should I return it to Midland they will test it a say no fault found.  

Anyone experienced the squelch issue with the MXT-575?  Any ideas on cause or correction?   

[nokones]

Don't ground your radio negative power lead directly to the battery.  Ground the radio negative power lead to a factory chassis grounding point.

[WRYZ926]

Since this is in your vehicle, I have to ask.

Does it only happen when the truck is running?

The reason I ask is that you stated that you do not have an issue when the radio is connected to a power supplying your house. This makes me think that you are getting interference from your truck.