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Motorola CDM1250

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#1
So I have a CDM 1250 and a PM400 . With the CDM 1250 with a remote head setup I have a low alternator whine when I transmit . When I plug the PM 400 into the same power plug, hook the same antenna into it and plug the same mic I was using on the CDM 1250, no whining when I transmit....

I paid good money for the CDM 1250 and I would prefer to use it!

Any ideas???

Thanks!!
 

SteveC0625

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#3
So I have a CDM 1250 and a PM400 . With the CDM 1250 with a remote head setup I have a low alternator whine when I transmit . When I plug the PM 400 into the same power plug, hook the same antenna into it and plug the same mic I was using on the CDM 1250, no whining when I transmit....
Try re-routing the remote cable that runs between the head and the radio unit. If it is laid along other wiring it can pick up alternator whine.
 
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#4
Tried that still no luck unfortunately it's 20 meter long cable. Think a 3 meter would be better? And what about going directly on the positive on the battery rather than the jump box
 
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#5
So I attempted to try to change the ground on the deck of the cdm 1250 , one problem I disconnected the ground and it still is powered on..... Also I tried moving the hot directly to the battery with no change in whine when I key up on and listen through another radio.

I'm at a loss here . I've read a few places that CDMs that are not remote mounted do not have that problem ..

Any other ideas ???
 
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Messages
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Location
East Texas
#6
Install a noise filter

You should be able to find a noise filter at any auto parts store. Tell them it is for alternator whine. Mount it in line of your power wire as close to the radio as possible.

So I attempted to try to change the ground on the deck of the cdm 1250 , one problem I disconnected the ground and it still is powered on..... Also I tried moving the hot directly to the battery with no change in whine when I key up on and listen through another radio.

I'm at a loss here . I've read a few places that CDMs that are not remote mounted do not have that problem ..

Any other ideas ???
 

SteveC0625

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#7
So I attempted to try to change the ground on the deck of the cdm 1250 , one problem I disconnected the ground and it still is powered on..... Also I tried moving the hot directly to the battery with no change in whine when I key up on and listen through another radio.

I'm at a loss here . I've read a few places that CDMs that are not remote mounted do not have that problem ..

Any other ideas ???
The Motorola install manual specifies that the hot should be on the battery, fused of course within 12" or so of the connection.

Ground should be to an existing vehicle body ground point. I like the one near the battery.

Of course the radio is still powered on when you disconnect the ground. It is still grounded through the antenna coax to the antenna mount. Bad juju to try to transmit if the hot is disconnected!
 
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#9
The Motorola install manual specifies that the hot should be on the battery, fused of course within 12" or so of the connection.

Ground should be to an existing vehicle body ground point. I like the one near the battery.

Of course the radio is still powered on when you disconnect the ground. It is still grounded through the antenna coax to the antenna mount. Bad juju to try to transmit if the hot is disconnected!
Ahhhh didn't even think of the antenna grounding the radio duh...

I'm gonna try what you said and go directly off the battery and use a good ground point by itself .

Still will try the filter, we'll see what happens .....
 

SteveC0625

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#10
Ahhhh didn't even think of the antenna grounding the radio duh...

I'm gonna try what you said and go directly off the battery and use a good ground point by itself .

Still will try the filter, we'll see what happens .....
Use an existing factory grounding point. There are usually several good ones near the battery. Coat the ring terminal with dielectric grease. I always use uninsulated terminals on hot and ground. I use the right correct ratchet crimping tool, then solder, and finish up with heat shrink.
 
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#11
Well I tried seeing if i put it back into a single unit rather than remote if it would eliminate the noise. No luck ,unfortunately I left it plugged in when I made it remote mounted again and I fried something . So now it only works as a complete unit unless I get another remote kit ...
 
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2,548
Location
New Orleans region
#12
My bet is the noise is coming in via the ignition power feed. That probably is where you need to put the filter in line with. Have seen this happen in a number of radio installations.

Most of the companies have limited filtering built into their radios on the ignition feed line. Bad part of this is that many radios use this feed as the source for their voltage regulators for the rest of the radio.
 

cifd64

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Northern Passaic County, NJ
#13
Are you using any additional accessories? Ext speakers, ignition sense, etc?

I have installed many of these, what works for me is using a fused pigtail right into the fuse box (might have to do some clever maneuvering.) ground it normally. Make sure you go to the right fuse (either constant or accessory, depending on your needs) and that you get 12v. If you are using both the PM and CDM, use seperate power sources and fuse leads. Also, check all of your cables for frays and bights. If the remote, power or other cables are run along door openings, in rocker panels, headliners etc, you may have pinched something when putting those items back in place (Both metal and plastic support clips are strong enough to severe those cables. Depending on the car, space is limited.

Trace all cables.
 
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Messages
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Denmark, ME
#14
Looked it over again. I only can use the CDM 1250 if its out of remote mount mod.Like I said I left it plugged in when I went to go back to remote mod I left it plugged in and something fried cause it sparked on me. So until I get a new remote head kit it has to stay 1 unit which sucks.

ANYWAYS though, plugged it in to the power what not and still hearing the whining. So I put the PM400 back in, key up on the mic and what do I hear in my other radio? No Whining in the background.....

Still at a Loss. It makes no sense to me why One radio would have the Whine in the background when transmitting and the other one doesnt..
 
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