New GMRS install & interference

[slim_pickens]

Hey guys, need some help with my new GMRS setup.

This weekend I installed the 15w Midland MXT275 install following fairly closely to an install by a fellow Jeeper over on the 392 forums (see here). I've got the base unit mounted behind the passenger kick panel (a little tricky, admittedly), the Midland 6db whip antenna mounted on a bracket hanging off my driver's side front cowl, and I'm providing power to the base unit using an aftermarket 12v adapter harness that plugs into the back of the 12v outlet in the front console near the climate controls. I've also run a Cat 6a ethernet patch cable with a bulkhead adapter mounted on the right side of the console trim so that I can plug the Midland microphone unit into this bulkhead.

My low-profile Midland coax cable was custom-cut to 10' by CoolTech at my request, and this turned out to be just about the perfect length. I have only about 18" of excess and this is just folded up in the upper right corner of the passenger footwell.

My problem is, I have pretty bad interference whenever I'm receiving. Although I can hear transmissions from others "OK", there's a constant medium-pitched whine that is a bit louder than the talker's voice. I also notice an additional bit of interference associated with the engine since every time the Jeep shifts, this particular interference quickly rises & falls.

I have not had a chance to troubleshoot anything yet, but I at least seem to notice that this constant whine exists whether the engine is running or not. My first suspicion is that perhaps the 12v adapter harness I'm using (or that general location amidst all the electronics?) could be the problem so I'm first planning to try powering the Midland from a portable battery pack I have just to see if the problem is this power setup.

If this does identify the problem, it would be a bummer since some other people with Jeeps seem to have good luck with this kind of approach. Not sure why my luck would be different?

If that does solve the problem, I assume I'm OK to just run power directly off the starter battery but ground the Midland to one of the handy ground posts behind the passenger kick panel?

Thanks!

Sponsored

 

[bacon392]

" I have only about 18" of excess and this is just folded up in the upper right corner of the passenger footwell."

Only because you used the word folded and not rolled, are there any visible pinches in the coax?

EDIT: Also, you might want to try grounding to the chassis directly. Ground issues are often the cause of feedback in radio systems.

 

[slim_pickens]

" I have only about 18" of excess and this is just folded up in the upper right corner of the passenger footwell."

Only because you used the word folded and not rolled, are there any visible pinches in the coax?

EDIT: Also, you might want to try grounding to the chassis directly. Ground issues are often the cause of feedback in radio systems.

Hmmm. Interesting. The excess 18” is definitely not coiled in nice loops, but I’m not sure if it is clearly pinched as currently folded. I’d have to take a look to be sure.

 

[jhackathorne]

My setup is almost identical. Only difference is my ground is direct to battery and I'm running the 3dB ghost antenna and it's roughly the middle of my hood on a mount. I am running the 12V adapter and my unit is behind the glove box. I'm also not running the cat6, but doubt that would cause an issue.

Check and make sure there are no kinks in the coax. If there are none I'd try a new ground. That is likely the cause of the issue. Good luck hunting it down.

 

[slim_pickens]

My setup is almost identical. Only difference is my ground is direct to battery and I'm running the 3dB ghost antenna and it's roughly the middle of my hood on a mount. I am running the 12V adapter and my unit is behind the glove box. I'm also not running the cat6, but doubt that would cause an issue.

Check and make sure there are no kinks in the coax. If there are none I'd try a new ground. That is likely the cause of the issue. Good luck hunting it down.

Thanks! Regarding the ground, if you grounded the Midland to the battery, what did you do with the negative lead off the 12v adapter harness… just not use it?

Would it be worth it to see if grounding the Midland to one of the ground posts close by behind the kick panel does the trick, or is it clear that this is insufficient?

 

[jhackathorne]

Thanks! Regarding the ground, if you grounded the Midland to the battery, what did you do with the negative lead off the 12v adapter harness… just not use it?

Would it be worth it to see if grounding the Midland to one of the ground posts close by behind the kick panel does the trick, or is it clear that this is insufficient?

I honestly can't recall what I did with the one off the adapter. I just remember running the ground. I'd have to try to take it apart to tell you honestly.

 

[Ratbert]

Is there a reason you guys are putting the MXT275 near the glove box instead of behind the kick panel under the steering wheel?

 

[jhackathorne]

Is there a reason you guys are putting the MXT275 near the glove box instead of behind the kick panel under the steering wheel?

That is just where I had seen a video with good install instructions do it is all. This was nearing 2 years ago.

 

[jhackathorne]

That is just where I had seen a video with good install instructions do it is all. This was nearing 2 years ago.

And running the ground to battery was easier. Forgot about that part.

 

[davewald]

Mine is installed on the passenger side on *top* of the kick panel so that I can use both the built in speaker in addition to the speaker on the mic. That's a very useful option with the Midland. I have the aux switches, so am grounded to the wire provided with them. Perfect reception and transmission using both standard and the ghost antennas.

 

[TX_Ovrlnd]

Have you also tried ferrite cores on some of your wiring?

 

[dragoneggs]

I put my MXT-575 under the driver’s seat and grounded to a stud very close. A good ground is key. As others have said, a good coil (no kinks) of the antenna wiring is also something to watch. I have a fair amount of wire coiled up under the seat as well because my ghost antenna is relatively close by on the cowling just below the driver’s side A pillar. Clean signal both transmitting and receiving. I don’t think shortening up the wire is necessary. Check also your connectors. Usually where issues are vs. in the wire run itself.

 

[slim_pickens]

So quick follow-up... early this morning, I tried a few alternatives (engine off) to see if I could clear up some of the constant interference. Since nobody was broadcasting on my local repeater, I used one of the NOAA weather channels to judge things. Also, I am using male-female push connectors on the positive & negative coming out of the Midland to make these alternatives below easier:

1. I unbundled the excess coax cable in the passenger footwell and left it unlooped on the floor. No improvement.
2. I disconnected the Midland base unit negative from my 12v adapter harness and connected this to one of the currently-used factory ground studs in the kick panel area. No improvement.
3. I disconnected both the Midland base unit positive & negative from the 12v adapter harness and connected this up to the 12v cigarette lighter plug that came with the Midland and then plugged this into a portable battery station. "Maybe" some improvement, but not really sure.

I won't get to it for several days, but I guess my next scenario to explore will be to connect the Midland negative directly to my start battery as someone suggested above. Any other ideas?

EDIT: One thing I forgot to mention earlier but hoping is not a problem... I am also running a 6 AWG cable from the starter battery through the same clutch cylinder hole in the firewall as my GMRS coax is running. This 6 AWG cable is carrying ~35 amps while the engine is running back to a REDARC battery charger in the rear cubby for my aux battery. Since I'm getting this interference even with the engine off, I assume this isn't the main culprit...?

 

[jhackathorne]

I forgot to mention this, but I would also check and make sure your antenna is secure and there is nothing loose. Including the bracket you have it a mounted on.

Another option is to use the antenna that came with it to run your tests.

 

[CpT Papa]

You mentioned mounting the antenna to the cowl. How is the antenna grounded?

Sponsored