Installing a Motorola CDM1250

[cddavis]

I could use a little more help I just purchased a CDM1250 from another member on the board, I am looking for a low profile antenna (probably Antenex) in the upper VHF range (150 - 160). What type of cable and connector would I need?

 

[hawkspringsfire]

I believe you will need to mini uhf connector.

 

[Steve0625]

I could use a little more help I just purchased a CDM1250 from another member on the board, I am looking for a low profile antenna (probably Antenex) in the upper VHF range (150 - 160). What type of cable and connector would I need?

If you get something like the Phantom, it will require an NMO mount on the antenna end, RG-58/U cable and a mini uhf connector on the radio end. The NMO mount is pretty standard for most mobile antennas these days.


The whole cable can be purchased as a single unit, ready for installation so there is no need to try to crimp or solder at either end. They are all over ebay and places like the antenna farm have them, too. You probably can pick one up on here, also.

 

[cddavis]

Product NarrativeThe VHF Phantom low visibility antenna's exterior is made of high impact ABS plastic suitable for inside or outside use. It's field tunable and offers approximately 1 MHz bandwidth. Features include a gold-plated pushpin contact, O-ring seal in base and closed-cell foam mount pad that seal out moisture. The insert molded mount bushing will not leak. Ground plane is required. Frequency (MHz)^150-168


So if it only has 1MHz bandwidth, it can only do, for example 150 to 151 after it is tuned?

 

[Respondcode3]

The Phantom Elite has a 5mhz spread. Its the half football looking one. The benefit of low profile you loose in performance. If you want low profile a black NMO is pretty stealthy

 

[Steve0625]

So if it only has 1MHz bandwidth, it can only do, for example 150 to 151 after it is tuned?

That is pretty much correct for transmit. If you don't need a wide range of transmit frequencies, it will probably work well for you.


If you just need a wider spread on TX, this might work a bit better:


http://www.theantennafarm.com/catalog/index.php?main_page=product_info&cPath=191_192_195_457_211&products_id=778


Comes in 150-155 and 155-160.


There is also a Larsen that comes in a fixed 2 Mhz. spread (154.42 to 156.48). It should work well for fire and ems applications in that range.


http://www.theantennafarm.com/catalog/index.php?main_page=product_info&cPath=191_192_195_457_211&products_id=787


I am certain there are others out there, but I only looked at the antenna farm's offerings.


All three of these mentioned here should perform pretty well on the RX side over a wider range than they are spec'd for if you are not in an area that has communications challenges. But if you are in a fringe area, you would not be looking at low profile antennas.

 

[cddavis]

Thanks for the help everyone, unfortunately it doens't look like that will work for me. Someone had recommended this:


http://www.radio-accessories.com/mb8.aspx


and


http://www.radio-accessories.com/qwb152-antenex-laird-antenna.aspx


I know you will need to drill but does this setup sandwich the roof so that water doesn't get in? I don't understand what holds it from underneath. :bonk:

 

[Respondcode3]

the antenna is held by the fingers under the ring. The antenna is mounted by Drilling the right size hole and then feeding the cable into the hole then the mount is pushed into the hole the center is bigger than the hole so it doesnt fall in. The brass ring compresses the mount to hold it in place. There is a thin rubber gasket on the ring. If done correclty it wont leak. As a precauton I always use a thin rubber antenna gasket before mounting the whip.

 

[hawkspringsfire]

These might help you:

http://www.youtube.com/watch?v=zs-0EF7mP8k

 

[cddavis]

These might help you:

Thank you sir, that helps alot.

 

[cvfd1615]

Just go with a magnet mount NMO, yes it is always better to drill but since you don't seem to familiar with radios and stuff just stick a magnet mount on the roof and be done with it.


I definitely recommend a WHIP antenna over a CAN (junk) antenna anyday and I would never want to compromise performance over looks.

 

[Steve0625]

Not a bad demo for you to get started. But a couple of comments on the video.


1. I like to lay down a layer or two of masking tape where the hole is going to be so that when I drill, the bit does not chew up the paint around the hole. I want the gasket at the base of the antenna to rest on paint, not bare metal. It's an invitation to rust, and rust can interfere with antenna function.


2. Antennas work best with a ground plane of at least 15-20" in all directions. Placing the antenna at the edge of the truck roof eliminates about 45% of the ground plane. Ideally, the antenna should be in the center of the roof. If there is a ceiling light in the vehicle, you can drop it, pull the headliner down a bit and then drill just a few inches forward or rearward of the light. Feed the cable across the roof behind the headliner and drop it along one of the pillars.


3. I live in way upstate New York. They use a lot of salt on the roads in winter here, and it accelerates corrosion and can interfere with all kinds of electrical things in cars and trucks. For that reason, I coat electrical contacts with a light layer of dielectric grease. That NMO is a lot of bare metal and I would protect it well.


4. When you route the antenna cable down to the radio, be sure to protect it from any sharp edges of metal or plastic. I use rubber grommets when passing through a metal or plastic bulkhead. 1/4" loom is good for general protection. If the cable has to go outside the vehicle passenger compartment for any reason, make sure it is in loom out there. Same for your power cables out to the battery and ground and the ignition sense line. Protect them well.

 

[SlickTop Solutions]

Not a bad demo for you to get started. But a couple of comments on the video.

1. I like to lay down a layer or two of masking tape where the hole is going to be so that when I drill, the bit does not chew up the paint around the hole. I want the gasket at the base of the antenna to rest on paint, not bare metal. It's an invitation to rust, and rust can interfere with antenna function.


2. Antennas work best with a ground plane of at least 15-20" in all directions. Placing the antenna at the edge of the truck roof eliminates about 45% of the ground plane. Ideally, the antenna should be in the center of the roof. If there is a ceiling light in the vehicle, you can drop it, pull the headliner down a bit and then drill just a few inches forward or rearward of the light. Feed the cable across the roof behind the headliner and drop it along one of the pillars.


3. I live in way upstate New York. They use a lot of salt on the roads in winter here, and it accelerates corrosion and can interfere with all kinds of electrical things in cars and trucks. For that reason, I coat electrical contacts with a light layer of dielectric grease. That NMO is a lot of bare metal and I would protect it well.


4. When you route the antenna cable down to the radio, be sure to protect it from any sharp edges of metal or plastic. I use rubber grommets when passing through a metal or plastic bulkhead. 1/4" loom is good for general protection. If the cable has to go outside the vehicle passenger compartment for any reason, make sure it is in loom out there. Same for your power cables out to the battery and ground and the ignition sense line. Protect them well.

Just one thing to add, if you are installing the radio in a console of any type, make sure you have a sufficient service loop to be able to fully remove the radio without having to blindly play with any connections on the back of the radio.

 

[wkr518]

if you find you have extra antenna cable try to straighten it out in your install and not coil it up and zip tie it.RF bleeds out of the cable and may effect tx performance.and try to keep it away from any strobe power cabling.

 

[Steve0625]

Just one thing to add, if you are installing the radio in a console of any type, make sure you have a sufficient service loop to be able to fully remove the radio without having to blindly play with any connections on the back of the radio.

Great reminder! Best to leave a foot or so at the antenna end, too. (Forgot about those and the rf tip above.)

 

[cddavis]

Thanks for the help everyone.