CMX760 constant beep during TX

[Skudshark]

Hey folks, either my Google-Fu is weak or this is just something weird that I'm not finding anything on.

Picked up a CMX760 for my truck and ran a fire ring/fire stick to it and tapped the 12v accessory plug, everything seems to run fine and checked my SWR with the antenna and am in the green.

However if I transmit, there is a constant beep coming from the handset and oddly if I touch the metal mic hangar on the back, the beep turns into a lower tone.
Bad ground somewhere in the device? I've messed with every (limited) setting there is on it and can't seem to figure out why it likes to do this, my older Uniden never exhibited this issue.

Penny for your thoughts?

 

[mmckenna]

Do you have a proper SWR meter, and what does it show?

If the radio is doing this only when transmitting, it would lead me to believe the cause is one of a few things:
-Poor grounding. Do not rely on a long negative power lead or the coax shield for ground. Run a short as possible ground wire from the metal radio chassis to vehicle steel. Shorter is better.
-High SWR. SWR being "green" really doesn't tell us much, I don't know what kind of SWR meter you are using. High SWR can cause RF to get back to the radio and cause issues.
-Power issues, taping into existing wiring is usually not a great idea. Always best to connect the radio power feed directly to the battery. Tapping into existing wiring can introduce all kinds of interference.

 

[Skudshark]

Do you have a proper SWR meter, and what does it show?

If the radio is doing this only when transmitting, it would lead me to believe the cause is one of a few things:
-Poor grounding. Do not rely on a long negative power lead or the coax shield for ground. Run a short as possible ground wire from the metal radio chassis to vehicle steel. Shorter is better.
-High SWR. SWR being "green" really doesn't tell us much, I don't know what kind of SWR meter you are using. High SWR can cause RF to get back to the radio and cause issues.
-Power issues, taping into existing wiring is usually not a great idea. Always best to connect the radio power feed directly to the battery. Tapping into existing wiring can introduce all kinds of interference.

I had 1.5 on CH1 and just under 2 on CH40 shortening the antenna as much as I could to narrow those down. Was my understanding as long as both figures are under 2 it was acceptable. Novice here so I won't be surprised if I'm off lol. Ground wise it was tied into factory 12v accessory power and ground lead, so cable length isn't more than 2 feet.

Thanks by the way for the response!

 

[Skudshark]

Oh and it was an Astatic SWR meter.

 

[FiveFilter]

Two ways I would approach this:

1. Try the older Uniden on your truck using the same wiring, coax and antenna that you are seeing a problem with with the new Uniden. If the old Uniden works and the new one doesn't, then it must be the new Uniden's problem, which may indicate the need for warranty work. If the old Uniden doesn't work well either, then it must be your truck's set-up that is the problem; i.e., the antenna, coax, power source, grounding and etc.

2. Try the new Uniden in another vehicle with a known good-working antenna, coax and power source. If the new Uniden works well, then it must be your truck's set-up that is the problem. If it doesn't, then it may be time for warranty work.

 

[mmckenna]

I had 1.5 on CH1 and just under 2 on CH40 shortening the antenna as much as I could to narrow those down. Was my understanding as long as both figures are under 2 it was acceptable. Novice here so I won't be surprised if I'm off lol. Ground wise it was tied into factory 12v accessory power and ground lead, so cable length isn't more than 2 feet.

Thanks by the way for the response!

Sorry, just seeing this reply now….

Again, don't rely on the long power feed to ground. You need to try running a ground wire from the radio chassis directly to the vehicle steel. Should be as short as you can make it.

SWR sounds acceptable.

I agree with FiveFilters troubleshooting ideas. You need to isolate where the issue is, Is it the radio or is it something in the installation.

 

[ladn]

+1 on FiveFilter's advice.
I'd add try substituting a (known good) dummy load for the antenna and see of anything changes.