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Commercial Radio Antennas Please keep discussion related to professional, commercially used antennas and antenna systems for the two-way radio industry. Topics for the use of these antennas on amateur bands are accepted here.

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Old 11-25-2012, 2:05 PM
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Default Laird 1/4 wave on a Backrack

Good afternoon, I work as a mechanic for a relatively small fleet (25). I have been using the Laird 1/4 wave antenna with a spring on almost all of our equipment. I have to install a radio on a new F-250, and they do not want the antenna through the roof on this truck. It does have a standard Backrack, so I was thinking about mounting it there. I have never attempted this, so I was wondering if the performance would be acceptable from a Backrack mounted antenna (ground plane). I only know the basics about radios, so that's why I'm here. Thank you in advance. The radio going in is likely going to be a 40W CM300 or a PM400, on VHF around 151 Mhz
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Old 11-25-2012, 4:59 PM
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I have mounted VHF 3db gain and low band antennas on "L" brackets 1/4 inch bolts with "L" on the inside of bracket on the bottom rail the one that mounts to the bed using a sealed/shielded mount (Tessco 436486) to prevent rust etc. And have had good luck. if it wasn't so dark now i would get a picture from my truck to show you. I have done this 15 times or more for people and haven't had any issues with grounding or swr's
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Old 11-25-2012, 7:07 PM
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I did this on a truck once, and it worked. It is not ideal, but it will work fine. BackRack makes brackets for their racks that have the necessary 3/4 inch hole for the NMO mounts. A 1/4 wave antenna would work fine, just make sure its at the top of the rack and in the clear. Anytime you get the antenna down below surrounding metal, performance is going to suffer. I'd suggest making sure the rack is well grounded to the sheet metal. Running a piece of braid from the rack to the sheet metal might help performance and make it easier to tune, might not, but it won't hurt.

Center of the truck roof is preferred, but I understand some don't want a hole punched in the roof of a brand new truck. Just make sure you add a disclaimer to it when you install the antenna. The owner/driver should not expect it to work as well as an antenna mounted on the truck roof. Range and performance may suffer a bit since the ground plane is not ideal at your frequency.


http://backrack.ca/index.php?option=...&id=3&Itemid=4 Down near the bottom of the page. Likely you could fabricate this on your own easier/cheaper, but at least this gives you a good idea. One thing to consider is that since it's likely going to be out on the edge, you need to make the mount strong enough for getting hit by a branch, or someone using it as a tie down point.

Last edited by mmckenna; 11-25-2012 at 7:12 PM..
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