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CM-300 issue

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mfd4523

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Recently installed new CM-300 in my personal vehicle. Was a brand new install on 2012 silverado. Have a lightbar and siren also installed as this is for the fire service. Have noticed that the radio seems to have weaker reception then other cm-300's that I've have been around and after a radio check last night I am transmitting with considerable static. Have checked the antenna from radio to antenna and see no issue there and radio is on high power and correctly narrow banded. I believe the issue is how it's hooked up but not sure if that could cause the reception issue. The radio calls for a 15 amp power wire. Due to the other items I'm powering, I ran 1 30amp power wire and that powers my light, siren and radio as the three together don't pull that much amps. It has its own separate ground wire to a bolt though the floorboard. I figured a bad ground might cause that but normally when I transmit I have my light and siren going and I'm told I am clear and no static. Is it possible that when everything else is off that the radio pulls to much power and has static issues? Would that or a bad ground explain the weak reception? My minitorV pager has better reception that my mobile does.
 

mmckenna

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Noise on your power feed can certainly cause issues, but I doubt that is it. If you ran your power direct from the battery, then you should be good to go. One thing you can try is to disconnect (pull the fuse) for your siren and light controller. Then check your radio. While you are at it, check all the connections between the battery and the radio. Look for corrosion, lose connectors, etc. The radio should only draw a set amount of current on transmit. It should't change depending on the lights or siren running

I'd suggest having someone with an antenna analyzer check your system. There are many places that things can go wrong and cause issues. An SWR meter alone may not be enough. A shop with the proper tools and test equipment can save you a lot of headaches.

A couple of places to check:
Connector on the end of the antenna feed line, where it connects to your radio. An improperly installed connector can cause issues.
Pull the antenna off and check there isn't corrosion or moisture. This is a pretty common cause.
Check the antenna itself. A damaged antenna can be a cause.

Most of all, be sure it isn't your location.

Don't rule out the radio itself...
 

KG4INW

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Where do you have your antenna mounted and what type is it? Using an analyzer is an excellent suggestion.
 

mmckenna

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Yes, good question.

You say "Recently installed new CM-300 in my personal vehicle."
Who did the install? What sort of antenna, antenna mount, coaxial cable, and connector were used?

Pictures are worth 1000 words…..
 

cmdrwill

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Radio should have a separate battery feed fused for 15 amps for your CM300 radio. And a separate ground just for the radio near where the radio is mounted.

Check your antenna installation....
 

SteveC0625

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Here is a link to the Motorola install manual for the Pro Series. The chapters on power connections and such are generic to all of their commercial and professional radios.

https://drive.google.com/file/d/0BxAVX2o_3yDlSkJzak1MN251c00/edit?usp=sharing

They specifically want the +12vdc line to go direct to the battery's positive terminal with a fuse within 12" of the battery. The -12vdc (ground) is to go to a factory grounding point.

General advice is to always use a separate cable for the radio power, direct from battery to radio. Even though it might seem logical to combine main power, it's not advisable. (The exception is special package vehicles that have main power points in other places like the trunk on PPV and SSV units. They use wire that is rated a lot higher than 30 amps for this to avoid voltage drop and heat issues.

Since the Motorola power cables have equal lengths of red and black wire, most installers will pick a grounding point near the battery. There are usually several of them in the area.

FWIW, you may find a bad junction on the "30 amp wire" where the radio is connected to it. Or, the "30 amp wire" is actually less capable than you think. If I was going to try to create my own power point, I would have used wire sized for at least 50 amps or more between the battery and the power point. 75 or 100 amp would not be out of line. You can't just add up the current draw of the lightbar, siren, and radio to determine wire size. Length of run is critical. Installers usually use double or triple (or more) the anticipated current draw when sizing wire for this purpose.

I regularly install CM's, CDM's, and M1225's in cars and trucks. I follow the Motorola guidelines religiously and have never encountered the issue described by the OP.
 
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