Midland MXT275 installed...getting a whine (1 Viewer)

[geanes]

Installed my Midland MXT275 in the back of my 1998 LX470. It's mounted on the back driver side panel and plugged into the back 12v outlet via the included 12v plug. The antenna cable is a Midland NMO cable that runs along the driver side floor and then thru the firewall (with a bunch of other cables) and then out to the bullbar where the Midland 6db NMO antenna is mounted. I ran a CAT5 cable from the base unit all the way to the dash and connected into an RJ45 female/female connector. I am now considering wiring the unit directly to the battery vs using the 12v fused plug.

So, that's the GMRS setup. Now, I have the fridge power line running down the same path as both the GMRS antenna line and the CAT5 cable. The fridge is unplugged most of the time, but the line is connected directly to the battery.

When someone is transmitting to me, it's crystal clear. When I key up the mic, they get a noticeable whine/high pitch "weeeeeeeee" (whether I'm on Hi or Low power). It's happened on 3 different GMRS handhelds. I noticed this morning that when tuned to the weather, I get a steady low-level whine. It doesn't increase in amplitude with the accelerator or when LED lights are kicked on. I unplugged the antenna line and then hooked up the 2db antenna that came stock with the radio. Same whine in the same scenarios. So, that leads me to believe the power cables don't have anything to do with this as the stock antenna was nowhere near any of the power cables (I ran it straight out the back window and up onto the roof) and the antenna is not the issue either. I even plugged the mic directly to the base unit (bypassing the CAT5 extension) and the same issue persists.

Would ferrite collars on all of the lines make any difference? Considering picking up some from Amazon. What about some type of sheathing for the lines?

I am at a loss.

 

[1911]

Gary, these consumer-grade radios are not very well shielded. Ferrite chokes may help, bonding (grounding) your exhaust pipe to the frame with braided flat cable will help if it's ignition noise (varies with rpm).

You say that the antenna coax is routed next "a bunch of other cables"; if any of those are power lines for anything else in the vehicle then they could be a potential source.

In general, power straight to the battery is best for noise suppression.

It could be any or all of these things - they can drive you crazy. Sometimes, nothing works if the radio itself is not well-shielded. The quality control is pretty uneven with some consumer radios. Good luck with it.

 

[geanes]

Gary, these consumer-grade radios are not very well shielded. Ferrite chokes may help, bonding (grounding) your exhaust pipe to the frame with braided flat cable will help if it's ignition noise (varies with rpm).

You say that the antenna coax is routed next "a bunch of other cables"; if any of those are power lines for anything else in the vehicle then they could be a potential source.

In general, power straight to the battery is best for noise suppression.

It could be any or all of these things - they can drive you crazy. Sometimes, nothing works if the radio itself is not well-shielded. The quality control is pretty uneven with some consumer radios. Good luck with it.

Thanks for that info. Midland is sending me a replacement and I'll try that. I'm going to wire it direct to the battery and ground it as well there. I'm going to pull the antenna cable and reroute it through a different hole in the firewall with a dedicated boot. From there, I'll route it best to avoid close proximity to any power lines. But, it's hard to find a route that doesn't have some power line present. Figure as long as I avoid the big old 4 AWG fridge power line and the 8 AWG fuse box power line, I should be ok. We'll see how this replacement unit plays out. Midland said someone recently had the exact same issue and they sent them a replacement which worked perfectly and fixed the issue. At this point, I'm figuring it's a production issue on my unit.

This is my first foray into anything other than CB, so I'm a bit of a newbie

 

[LongDuck]

When you go to swap out the old for new do a quick check by connecting directly to the battery at the engine compartment. This removes the vehicle wire routing from the scenario and will rule out the radio being the problem. As others have mentioned, your choice to mount the base unit so far from the handset could be allowing a signal to get into your transmission and ferrite chokes may help on that, as well. Can't hurt to try.

 

[geanes]

When you go to swap out the old for new do a quick check by connecting directly to the battery at the engine compartment. This removes the vehicle wire routing from the scenario and will rule out the radio being the problem. As others have mentioned, your choice to mount the base unit so far from the handset could be allowing a signal to get into your transmission and ferrite chokes may help on that, as well. Can't hurt to try.

Thanks! Yeah, I ordered some ferrite toroids and will play around with those. I pulled the radio last night and direct connected to the battery and plugged the handset directly into the unit and installed the included 2db antenna....eliminated all install variables regarding 12v vs direct connect, length of lines, exposure to adjacent power lines, etc. The exact same whine emitted when transmitting and tuning into the weather channel. Definitely seems like something is "up" with the radio itself. 3 buddies have the exact same radio and similar configuration and don't experience any whine at all. Definitely curious to see if the replacement unit "cures" the issue. But, I'll have ferrite toroids if necessary.

 

[geanes]

@1911 @LongDuck ...... received my replacement MXT275 today. I didn't unhook any of my install. I simply took the new handset and plugged it into the same connection in my dash. Zero whine or interference. Crystal clear on transmit and receiving weather.

Took the handset from the original unit and plugged it into the new base unit. Attached new antenna and plugged into separate power. Whine and interference same as before. The handset/mic is the culprit.

Not sure what in the handset is wrong. Might crack it open and see if I can figure it out. But, at least I have a properly working radio now.....technically 2 properly working base units and 1 properly working handset.

 

[1911]

Glad that you got it sorted out that easily.