GMRS not transmitting while engine running (1 Viewer)

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Joined
Aug 12, 2022
Threads
5
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18
Location
Logan UT
I have a strange issue with my new radio install. I installed a KG1000g+ in the storage box under my driver seat and remote mounted the face on the dash. I connected the power to a spare spade with constant power on my fuse box. Grounded to the screw mounting the radio right under the seat. I’m running a midland ghost antenna mounted to the apron right below the hood. If the engine is off then it transmits and receives just fine. Even when I turn the key on and just don’t crank the engine, it works just fine. As soon as I have the engine running I can receive but not transmit.

I have swapped to a magnetic mount antenna and just put it up on the front fender to see if my antenna wire was running by something giving it interference. Came back with the same issue.

I ran a jumper cable from negative battery post and clamped it right to the ground wire to see if I have a weak ground… same issue.

I haven’t messed with the power side yet.
 
I would test it by running a jumper to the battery positive and see if you have the same issue. If so there might be a defect in the radio. Next in line would be testing the antenna, do you have another you can use or borrow? You might have more interference with the motor running and its effecting the ghost antenna (which work, but have mixed reviews as well).

Sounds roughly like what this user is experiencing as well: MXT275 Receives but doesn't Transmit - https://forums.mygmrs.com/topic/2415-mxt275-receives-but-doesnt-transmit/#:~:text=Try%20resetting%20the%20unit%20back%20to%20its%20original,hold%20the%20PTT%20and%20the%20Weather%20button%20simultaneously.. However, after a quick skim through sounds like they do not have a solution, but sometimes its nice to know you are not alone, haha.

I am going to wait for wiser minds in the radio world to chime in too though.
 
Is the fuse connection rated for say 10 amps? What about the power cord for the run from the fuse block? Is there another load on the same fuse while the engine is running?
 
I have been experimenting to narrow down the problem. I have run power and ground wires straight to the battery. The fuse on the positive side is 20a I believe (it came with the radio), same issue. I bought a browning noise filter and wired it to the power and ground, same issue. I have hooked up a different midland radio I have and same issue. I have connected a different antenna with a mag mount, same issue. The only thing I have found that changes anything is I connect the radio to an external battery not connected to the vehicle. I have one of those Jackery portable battery things and if I hook the radio to the 12v power on that it works great. There is something being put off by the alternator or the spark plugs or something that is causing interference with the power source.

I am thinking I might try a new alternator and see if that helps. I am wanting to upgrade to a bigger one anyway. I found a 50a unit on City Racers website that I might try.
 
I have been experimenting to narrow down the problem. I have run power and ground wires straight to the battery. The fuse on the positive side is 20a I believe (it came with the radio), same issue. I bought a browning noise filter and wired it to the power and ground, same issue. I have hooked up a different midland radio I have and same issue. I have connected a different antenna with a mag mount, same issue. The only thing I have found that changes anything is I connect the radio to an external battery not connected to the vehicle. I have one of those Jackery portable battery things and if I hook the radio to the 12v power on that it works great. There is something being put off by the alternator or the spark plugs or something that is causing interference with the power source.

I am thinking I might try a new alternator and see if that helps. I am wanting to upgrade to a bigger one anyway. I found a 50a unit on City Racers website that I might try.
you could pull the alt belt and try.
 
There's also a voltage difference between running or not, besides the electrical interference possibility. I'm not an electronics expert so I don't know if 12 V not running vs 14-15 V engine running would affect it.
 
I followed gnob's suggestion and pulled off the belt. Everything worked perfectly. I am not sure if a new alternator is going to be any better. Like I said I have been wanting to upgrade anyway so I will order that one from City Racer and give it a try. On a side note, do I need to upgrade any of the wiring for that alternator to handle 50a as opposed to the original 30a? Anyone have experience with this? I will search around on here and see if I see anything about that.
 
I followed gnob's suggestion and pulled off the belt. Everything worked perfectly. I am not sure if a new alternator is going to be any better. Like I said I have been wanting to upgrade anyway so I will order that one from City Racer and give it a try. On a side note, do I need to upgrade any of the wiring for that alternator to handle 50a as opposed to the original 30a? Anyone have experience with this? I will search around on here and see if I see anything about that.
check the alternator for AC output
 
I would check the power output at all conditions on the fuse panel where you are pulling power from....and if not a power problem then it would seem to be a radio issue. I don't follow why it would transmit on one condition of he engine running vs. not running if power feed is the same..
 
I ran wires straight from the battery to the radio bypassing the fuse box altogether for both positive and ground. I also tried the Wouxun radio as well as a Midland I have from another vehicle. With the alternator working I can not transmit with either radio. With the Alternator belt removed, it works perfect. My best guess is the alternator (or maybe the voltage regulator) is not very well shielded. I don't even really know what I mean by "shielded", electricity is basically magic as far as I understand. I have a new Alternator showing up tomorrow. Once installed we will see if it makes any difference. I am not sure if a new unit would be any better shielded than an old one from '73 but it's worth a shot. Like I said before, I have been wanting a few more amps anyway.
 
Long shot:
Did you check to see if you can hear a lot of noise if you disable the squelch on the radio? Maybe the alternator is giving out noise (although it's not obvious it would be in the UHF range), and some radios have a setting that disables transmit if the frequency is "busy". That could explain the no-transmit situation. Easiest would be to check and see if that setting is enabled and then disable it to check for improvement.

As to the increase in voltage with engine running, a 12V mobile radio in good condition should be able to handle variations from an alternator in good condition easily. From memory, I think mine is rated for input up to 15V or so. (Did you check to see what voltage the alternator is giving out? If you get too high a voltage that could explain the radio shutting off?)
 
The new alternator showed up today. Installed and now the radio works perfect with engine running or without. No changes to any radio settings. Not sure exactly what the old Alternator was putting out there to cause the transmission interference but it's solved now.
 
The new alternator showed up today. Installed and now the radio works perfect with engine running or without. No changes to any radio settings. Not sure exactly what the old Alternator was putting out there to cause the transmission interference but it's solved now.
replace your feed to battery if you jumped to the higher amp unit.

your old alt likely was pushing ac voltage due to diodes failing.
 

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