CM300 Problem

[SteveC0625]

I'm currently working on getting some CM300's installed in our highway department trucks. Up until yesterday, everything went fine. On the newest deuce and a half truck, there was no radio to replace so it's a clean install with a new power cable and antenna.

I double-checked power and ground and made sure the antenna was installed correctly using a meter to verify no shorts. The radio is programmed identically to 9 others. The radio powers up normally and appears to be working fine. However, after one test transmission on the highway channel, transmit stops working. The red TX light comes on but the radio just chirps a couple of times. There is no transmission. All the other channels in the radio continue to transmit properly on multiple radio checks. I can only guess that this chirp is some kind of error message, but I can't find anything about it in any of the maintenance or operator's manuals.

I've swapped out radios 4 times and each radio performs identically in the new truck. As soon as I put any of the radios into another truck or on the bosses' desk, it transmits just fine on the highway channel as well as all others. All of the radios were cloned from the first radio installed which has been in service for 4 months now with no problems so I know the programming is OK.

SWR is OK but not great at 1.3:1 - the boss insisted on a mirror mount for a quarter wave so that's the best we're gonna get there.

Anybody got any insights on this?

Thanks.

 

[mmckenna]

Is there anything different about that specific channel as compared to the others? More TX power, frequency different than the rest of them considerably?

My first gut reaction is that there is either a power issue (unlikely), like a bad ground or it's being voltage starved.

My second gut reaction is that there is an SWR issue. While your meter might show there isn't a short, that doesn't mean all is OK. Could be something simple like a ground that isn't good enough, the 1/4 wave antenna not actually making contact with the center of the antenna mount, etc.

Shining some light on this specific frequency would probably help. The fact that 4 other radios behaved the same way suggests there is some specific fault in that truck.

 

[N1GTL]

The problem is in that truck. Not the radio, not the programming assuming what you said about them all being programmed the same is accurate.

High swr will shut the radio down. Mirror mount 1/4 wave? Ditch that! When you check the swr, is the door opened or closed? I have seen that make a HUGE difference.

Did you check for a short on the antenna connector from the center pin to ground?

Did you check with a meter from the center pin on the antenna connector to the antenna?

Put a 1/4 wave mag mount on the roof and test it. The problem is antenna/transmission line related OR RF is getting back into the radio because of the positions of the antenna/radio.

 

[llu727]

The 2 chirps is a "low battery" error, just like in the portable.

I would start measuring the 12v while transmitting


BJ

 

[N5XPM]

Power problem on the right track

I experienced a similar problem on an install where power was obtained through a circuit breaker.
Current draw on TX exceeded the circuit breaker rating, which automatically reset when PTT was released.
It was a very frustrating problem.
I would also try magnetic mount antenna on the roof temporarily (and outside, not near the ceiling or a wall) to ensure that is not causing more problems.

 

[cabletech]

From what you said in the first post, I would say that 1) the antenna is just fine. I have installed antenna on a door/mirror mount for years and never had a problem.

2) the chirp you hear is an indictaion of low power as mentioned by n5xpm.

Where did you connect the main power lead too? You should take it to a battery tap off point under the hood. Also, for ground where did you take it? You can go anywhere on the frame of the cab as long as you remove the paint and get to clean metal, you do not need to go to the battery.

 

[SteveC0625]

2) the chirp you hear is an indictaion of low power as mentioned by n5xpm.

Where did you connect the main power lead too? You should take it to a battery tap off point under the hood. Also, for ground where did you take it? You can go anywhere on the frame of the cab as long as you remove the paint and get to clean metal, you do not need to go to the battery.

The truck is pre-wired for a two-way with hot and ground leads in the overhead console. One of the highway guys did the rough install. I am going back in the morning to add an improved ground direct to the cab as you recommended. It was next on my list anyway. If that doesn't solve things, then it'll be a whole new hot lead direct to the battery.

I am still puzzled by the fact that only one frequency out of ten in the radio is doing this. Every other channel in the radio works fine on TX.

Thanks to all for ideas and suggestions.

 

[SteveC0625]

Is there anything different about that specific channel as compared to the others? More TX power, frequency different than the rest of them considerably?

They're all the same TX power. The problem channel is 151 mhz while the others are either 155 or 159. Antenna is cut for 151 as that is the highway dept's primary channel. The others are mostly there for listening, not tx.

My first gut reaction is that there is either a power issue (unlikely), like a bad ground or it's being voltage starved.

See my previous post. Ground is next to be worked on.

My second gut reaction is that there is an SWR issue. While your meter might show there isn't a short, that doesn't mean all is OK. Could be something simple like a ground that isn't good enough, the 1/4 wave antenna not actually making contact with the center of the antenna mount, etc.

Shining some light on this specific frequency would probably help. The fact that 4 other radios behaved the same way suggests there is some specific fault in that truck.

I tested the antenna from the center pin of the mini uhf to the antenna so I know the spike is connected. I'll take a closer look at ground there, too.

 

[kayn1n32008]

Wirelessly posted (Mozilla/5.0 (BlackBerry; U; BlackBerry 9780; en-US) AppleWebKit/534.8+ (KHTML, like Gecko) Version/6.0.0.600 Mobile Safari/534.8+)

If it persists try a 1/2wave antenna

 

[SteveC0625]

The problem is in that truck. Not the radio, not the programming assuming what you said about them all being programmed the same is accurate.

They're all cloned off the radio that has been in the bosses' truck for several months.

High swr will shut the radio down. Mirror mount 1/4 wave? Ditch that! When you check the swr, is the door opened or closed? I have seen that make a HUGE difference.

Door closed.

Did you check for a short on the antenna connector from the center pin to ground?

Yes, checked ok.

Did you check with a meter from the center pin on the antenna connector to the antenna?

Yes, OK as well.

Put a 1/4 wave mag mount on the roof and test it. The problem is antenna/transmission line related OR RF is getting back into the radio because of the positions of the antenna/radio.

If the ground change doesn't fix it, I'll take a close look at this.

 

[mmckenna]

I'd be wary of "pre wired" stuff. Unless you know for sure that it is rated for the amount of current you are pulling on TX, then I'd run a new circuit all the way. Those prewired installs in the cab might be intended for a CB, and not for a higher powered radio. An owners manual for the truck in question would probably tell you for sure, or take a look at the fuse block and see what type of fuse/circuit breaker is there.

The Motorola radios usually come with a very nice wiring harness that will do the trick nicely. Since this is starting to look like a power supply issue, I'd just save yourself a service call later and just install the correct wiring and bypass the pre-wired circuit. Ground to the body, positive side to the battery or correct tap point and of course the fuse at the battery/tie in point. Then at least you'll be able to rule that out.

Until you know for certain you have a good clean power supply capable of supplying sufficient current to the radio, I wouldn't do anything else.
And why it works on the higher frequency and not the lower, the radio will be more efficient at some frequencies and less on others. Sounds like your power source wiring is just at the edge of what it's capable of.

 

[gtaman]

Try not to mount it in the overhead slot. I had and issue once where a radio kept resetting and not working in an overhead mount. The wireing in the roof interfered with it. I ended up mounting on the dash with all new wireing and it works fine now.

 

[ramal121]

This is getting lively, so I'll chime in. It does sound like a power problem so continue checking that avenue.

I'll throw this out though. Radios will twist off when blasted by their own RF (ever had a loose mini uhf connector)? This can happen even though the antenna is good and reflected power is low. By luck of the draw a voltage node (and they appear all over a ground plane) will wind up on a device and drive it crazy. The exact proximity of antenna to radio may be your downfall. I have seen this with radios and with vehicle electronics.

Can you stick on a dummy load, or as suggested a mag mount as a go/no-go check. Or maybe move the mirror mount as best you can?

Good luck, stuff like this drives me up the wall.

 

[llu727]

Just a way off the wall thing - I have see where the mirrors are not at ground potential. It beats me why, but apparently it can be resistance in the door hinges. Easy enough to check with an ohm meter from connector shell to true ground in the vehicle.

Another thought is those "prewired radio power" connections are set up for CB radios. Very light gauge wire.

BJ

 

[cmdrwill]

Another thought is those "pre wired radio power" connections are set up for CB radios. Very light gauge wire.

BJ

Exactly, wire size too small.
Run the correct power cable that comes with the radio, Red direct to battery thru the provided fuse. Black to the closest solid ground.

 

[SteveC0625]

Exactly, wire size too small.
Run the correct power cable that comes with the radio, Red direct to battery thru the provided fuse. Black to the closest solid ground.

Done all around. Spent the morning in a cold storage shed rewiring all the power for the radio. It stopped low voltage chirping as soon as I ran a fresh ground to cab steel.

Thanks to all. Next time, I'll just do the whole thing myself instead of letting the customer "help."

 

[lifeisgoodoneasystreet]

2 chirps

The 2 chirps is a "low battery" error, just like in the portable.

I would start measuring the 12v while transmitting


BJ

The problem IS the voltage on the vehicle. It's not seeing 13+ Some models, the CDM's are very fussy with voltages, will not perform or program on 12v, they want to see 13-15 volts. Hotter, the better As far ad the 1 frequency goes, it's the 151, antenna cut for will see the highest power forward, thus pulling more amps, lowering the voltage even more. Put a watt meter in line along with a volt meter clipped in the dc line and watch what happens. I think your problem will be solved.

 

[SteveC0625]

The problem IS the voltage on the vehicle. It's not seeing 13+ Some models, the CDM's are very fussy with voltages, will not perform or program on 12v, they want to see 13-15 volts. Hotter, the better As far ad the 1 frequency goes, it's the 151, antenna cut for will see the highest power forward, thus pulling more amps, lowering the voltage even more. Put a watt meter in line along with a volt meter clipped in the dc line and watch what happens. I think your problem will be solved.

Thanks for the advice, but we solved that problem back in

DECEMBER 2012

Hint, it pays to check the dates on threads before jumping in with both feet.