Motorola CommandPlus Loud Hum

[motodudeHT]

Our dispatch center has a Motorola CommandPlus and recently we discoverd that when transmitting there is a loud hum. When we disconnected the goosneck mic (Sure VR300?) and use the internal mic it stops the hum. Is anyone familiar with this unit that can help? I was thinking that the mic have some sort of pre-amp to boost the signal and may have a problem with it. We have tried different mics and that hasn't eliminated the problem. Any help would do. Thanks.

[Jim202]

Did you ever think that the cable where you plugging in may have a problem?

Jim

Our dispatch center has a Motorola CommandPlus and recently we discoverd that when transmitting there is a loud hum. When we disconnected the goosneck mic (Sure VR300?) and use the internal mic it stops the hum. Is anyone familiar with this unit that can help? I was thinking that the mic have some sort of pre-amp to boost the signal and may have a problem with it. We have tried different mics and that hasn't eliminated the problem. Any help would do. Thanks.

[motodudeHT]

That is possible. I am not exactly familiar with the console itself, but I'll check that out and look into it. Thanks.

[RFguy]

With external mic hum I would look for an open shield or a ground loop.

[RKG]

Or an impedence mismatch.

[The Pager Geek]

For giggles, disconnect the ground from the back of the Command Plus. See if it goes away. If it does, it is a ground loop. (Like suggested above.)

I've had at least 3 due to various reasons.

tpg

[KE9GK]

I maintain 4 of these things...both at a local PD and have 1 at home to play with....and NEVER have I had a noise issue like this on either. Now on a centracom...thats a different story! Did you recently switch over to the VR300 boom mic...or is it something you have been using for quite some time and just now noticed the noise? The reason that I ask is that there are jumpers on the main board in the console dealing with external mic impedance and gain that may be incorrect. When you say you have tried other mics, did you mean that you procured and plugged in a brand new VR-300 meant for the console, was it an "aftermarket" mic, or did you just replace the mic element on the top of the gooseneck? All these factors could make a difference. When these mics die...they die hard and quickly...typically w/o any warning...so a known good mic is a must when chasing "humming" issues. I agree with the above post - remove the ground from the console and see what happens....also if you did the soldering on the phono plug...remove the braid from the negative side and see what happens....this solved a similar problem in a centracom I was dealing with about a year ago. Strange thing is...a ground loop isnt that common on one of these because the physical gooseneck and element aren't directly grounding to the chassis because it is plastic where they want it to be mounted.

Hope this helps.....PM me if you need further assistance...I may have some other ideas if this doesn't help!

-gk

[talviar]

Although my agency owns one of these things we don't use it much (used as a backup in case the consoles totally crap out).

One thing I remember (you may already have encountered this) You have to disable the internal mic for the external mic to work correctly. If external connected and internal enabled I seem to remember load hum on transmit.

There should be a menu option somewhere on the Command Plus screen to turn off the internal that may/may not resolve the issue but worthy of trying.
Been too many years since I last used our command plus to remember how to do that though.

Tony