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Antenna confusion !!

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#1
Hello all, Installing my first mobile radio and researching what antenna to use. There seems to be alot of options and I am trying to understand, but not much luck. I have a CDM1250, vhf band (using for volunteer fire dept). Going on a 2012 F150. Any help with what antenna to get would be greatly appreciated. Thank You.
 

n0nhp

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#2
If it were my rig, I would put the antenna in the center of the roof of the truck, and use an NMO mount. If you are just using a single freq or freqs within 2or 3 MHz of each other the three db Laird / Antenex B1323S. or optionally without the spring. Wider band antenna will drop a bit of gain is the Laird / Antenex B1322WS.
I am partial to these antennas due to our shop installing several thousand over the years, there are other brands and less expensive brands, YMMV.

ps don't worry about drilling a hole in the cab causing the vehicle to lose re-sale value, if done by a professional and with the antenna base removed and a watertight plug in place, most dealers will never even notice or if they do notice, care. It is worth the small amout a dealer will charge to drill and install the antenna base and coax.

Bruce
 

SteveC0625

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#3
Hello all, Installing my first mobile radio and researching what antenna to use. There seems to be alot of options and I am trying to understand, but not much luck. I have a CDM1250, vhf band (using for volunteer fire dept). Going on a 2012 F150. Any help with what antenna to get would be greatly appreciated. Thank You.
Use an NMO mount in the center of the roof.

Before you buy an antenna, consider your needs for coverage. If you are not dealing with fringe transmission and reception, you may be better off with a 1/4 wave antenna. It won't stand as tall as a gain antenna, but you'll have a lot less problems with damage to the antenna in garages, etc. with the shorter one. A typical 1/4 wave antenna for the Fire/EMS VHF bands is usually about 17" tall, give or take a bit.

I keep a stock of Laird 1/4 waves here. They're mostly the black ones which are a bit more stealthy in appearance. My F250 has a VHF and a UHF 1/4 wave on the roof, and you have to look closely before you can even spot them.
 
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#5
I'll echo what was said above, but add a bit more.

Center of the truck roof is best. It gets the antenna where it will work best. The roof provides the full ground plane the antenna needs to work properly. If you do it correctly now, it will outlast your truck. There is a very good reason that all the public safety and professional installations you see will use a properly installed antenna.

As for what antenna to choose, someone has probably already done the work for you. Just take a look at whats on top of the fire apparatus. Use what they used and you'll likely be in good shape.

A couple of other things.....

-The licensee on the FCC license for your agency is the only one who can authorize adding radios to the system. While you may work for the department, that doesn't mean you can add radios without the licensees permission. Make sure you get something in writing, on agency letter head, signed by the top guy, saying you have been authorized.
-Don't add any neighboring departments without written authorization. See above...
-Make sure everything is done correctly, programmed right, and set up properly. Making a mistake can cause interference. Don't be "That Guy". You never want to be "That Guy".

You can program these radios with receive only channels. It might be handy to program in the NOAA weather channels, and maybe any other agency you want to monitor. Just make sure it's set to RX only.

As for the antenna mount install, absolutely. Drill the hole, do it right and you'll never be disappointed. Seen too many guys do half way installs, magnetic mounts, glass mount, some cheesy bracket off the bed or hood. They'll work, but they look unprofessional and the performance suffers. If you are not comfortable doing the antenna mount install on your own, get someone to do it for you, it really is worth it.

Always, always, always connect the power for the radio to the battery. Never ever tap into existing wiring, or worse, use the cigarette lighter plug. This is the quick way to screw up your install. Direct to the battery provides ample clean power to the radio. If you require the radio to turn on/off with the truck, use pin 10 on the rear connector and program the radio to use the ignition sense function. You'd wire pin 10 to an ignition controlled circuit (or a timer) and it'll turn on and off with the truck.

Also, while the CDM front firing speakers are really good, consider adding an external speaker. It really improves sound quality, intelligibility and you'll have no issues what so ever driving down the highway with all your windows down.

I'll add that I'm running a CDM-1550 in my 2011 F-150 with a quarter wave VHF whip mounted in the center of the cab roof. Never had an issue with it and it works very well. The control head for the radio has been remote'd under the dash board. The RF deck (radio guts) are behind the rear seat.
The antenna is flexible enough that if it hits a parking garage roof or tree branch, it just bends over and springs right back.

Here's the CDM-1550 with a Kenwood NX-900 800MHz control head under it:


Here's the NMO mount going in. Center of the cab roof:


Here's the head on shot. This was before I added the Kenwood:

 
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#7
any tips on the headliner in the truck, mmckenna? as far as removing for the cable.
I didn't need to remove the headliner.

I drilled the hole and routed the cable backwards down the center trough that's under the roof. I removed the rear dome light and there's a hole behind that that I was able to grab the cable and route it down the back pillar of the cab to the radio.
 

SteveC0625

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#8
any tips on the headliner in the truck, mmckenna? as far as removing for the cable.
You almost never have to remove a headliner to install an NMO and coax in the roof of a car or truck. If there's a light fixture in the center of the ceiling, you can drop that with just a screwdriver. That will allow you to flex the headliner downward a few inches to make sure you don't drill through the headliner. Depending on space and such, you may be able to position the antenna above or immediately next to the light fixture.

You can pull away the door gasket which will release the headliner on the sides if needed. I usually do that so I can be sure that the coax does not interfere with any airbags. If you have to route coax past an airbag, make sure that coax is between the roof and the airbag so that it won't interfere with the airbag deploying. It also makes it easy to pull the coax across the ceiling to the B or C pillar. On some vehicles, you can pull the gasket and tuck the coax behind the inside panel of the pillar. The door gaskets just push back into place these days.

If you search back here, you'll find lots of tips on installing antennas and radios into vehicles. Most of them are not vehicle specific so what techniques work on a Ford will usually work on any other brand of vehicle.
 

SteveC0625

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#9
Additional tip! If you purchase a hole saw, get the right one for the job. Most places that sell antennas and mounts offer the right hole for this task. If you go to Home Depot or similar and buy any old 3/4" hole saw, it will make a hole that is too large. They are sized differently.
 
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#11
thanks again guys, looks like I picked the right place for info. Planning on ordering the antenna by friday so hopefully next week ill be installing.
 
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#13
These guys are good. They'll have exactly what you need and they ship quickly.
http://www.theantennafarm.com/catalog/

Prices are good, too. Maybe not the absolute lowest, but they stand behind their stuff and are easy to deal with.

Don't cut corners and go with the cheapest mount/antenna you can get. I'd avoid the Tram/Browning brand names. They are Chinese made and of questionable quality.
Larsen is what I use at work and for my own personal stuff. Laird is good also. Both known good brands.

Also, unless you have the tools to install the mini-UHF connectors the CDM radios use, it would probably be a good idea to purchase the NMO antenna mount with the connector already installed. That'll save you some headaches.
 
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#16
On the back of the radio, the exposed pin is +. The shrouded pin is -.

This is done so the cable coming from the battery has the + pin shrouded and the - pin is exposed. Won't hurt if the - pin touches ground.

If it still won't turn on....

There are two things to look at:
These radios can be set up to do an ignition sensed power on/off. This required that switched (or even constant) +12vdc be applied to pin 10 of the 20 pin connector. If the radio was originally programmed with the ignition sense function, you'll need to apply power to Pin 10 to get the radio to power up. You can then reprogram the radio and take that function out, if you want.


Or, if you hook up the power backwards, there is a protection diode in the radio that will create a dead short if the polarity is backwards. This usually just pops the power feed fuse, but can damage the radio if the fuse is too big. I've seen similar Motorola radios blow the diode and take out the radio.

Probably a few other scenarios, but check the ignition sense first.
If you do not have the Motorola 20 pin or 16 pin rear connector assemblies, you can pick them up on e-Bay on the cheap:
Ignition Sense Plug Motorola CDM CDM1250 VHF UHF
This dealer is good, I've used him before. Just connect the red wire, through a fuse, to an ignition sense circuit, or directly to +12volts.
 
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