Question about mirror mount and SWR

[tonylopezx]

Hey everyone,
I drive a western star truck, and I have a few questions pertaining to SWR and mirror mounts.
The truck has a "stock" antenna receiver port that was built into the mirror of the truck that can not be modified as you can't disassemble the mirror it's sealed. The CB radio that is in this truck is a Uniden PC78LTW. The antenna used to be a 4ft fire stick I believe, however that broke and I wanted to upgrade the antenna to a metal one. I recently purchased a Browning 28 (63") antenna and it is for sure more heavy and larger than the light fiberglass Fire stick so I figured I'd be safe purchasing a mirror mount kit for more stability. IM NEW to the CB and scanner world, so please bare with me. With the Previous set up (fire stick at OEM mirror port) testing the SWR with the radio provided meter, I got 2.8ish or so, on ch1/20/40 which from what I understand is not good. Since I've installed this new antenna, I've also purchased new coax cable and ran it to the CB radio. The SWR is now over 3 in ch1/20/40. I've checked the cable for shorts, breaks, kinks and found none. Then I checked the mirror mount and noticed the coax screw cap (part where you screw onto the end of the antenna) was touching one of the mirror mount bolts. I fixed that, still high SWR, no change. I've checked to make sure the mirror is grounded into the cab of the truck, which it is through the bolts that attach it to the cab. The extra coax cable slack I have leading up to the cb radio is not coiled, however there is a lot of slack, I purchased 10' of cable, prob have a few feet in slack. The only other thing I could think of, is the nylon washer provided. I have mine on top of the mirror mount, is there suppose to be one below it too? I was only provided with one nylon washer. Also, will a high SWR affect RECEIVING signals, or only transmitting signals. thanks!
-Tony

 

[MBill]

Tony,

Here's a couple of things to try.
First, I would disconnect the antenna from the CB radio. Using a ohmmeter check between the outer
shell of the antenna cable connector and the center pin of the cable. If you get low resistance
reading of a few ohms or a few hundred ohms you have a shorted cable. Probably in the connectors,
though make sure the nylon insulator does indeed insulate the center threaded shaft of the antenna
from the mirror mount bracket. You normally only need the one nylon washer.
Second, you may have to tune the antenna. This depends on the type of CB antenna. Some have
a turn screw under the cap on the top of the antenna. Others you have to remove the cap and cut
a small amount of the antenna wire off; or you may need to lengthen the antenna. All depends.
The Firestyk website has a good review of how to tune their antennas and it would be good to go
there and read over what they say. Or check the website of the antenna you are now using. They
probably have information on tuning the antenna. There's a lot of knowledgeable folks on this
web site and I'm sure they can help you with more and better suggestions.

 

[tonylopezx]

Thanks for taking the time to help me out! I'll def try those ideas you mentioned. I've noticed if I put the new antenna in the factory mount on the mirror instead of the aftermarket one I can get an SWR of 2, which is better than over 3 haha. But 2 still seems to be on the high side? Also does SWR affect receiving signals or only transmitted signals? Thanks!
-Tony

 

[tonylopezx]

By the way, here is the way the mirror mount is setup, if anyone can confirm the nylon washer is indeed in the correct position so I can rule that out! Sorry you'll have to turn your head!

 

[jonwienke]

Assuming antenna is on the left and the coax on the right, the nylon insulator is installed correctly.

 

[tonylopezx]

Assuming antenna is on the left and the coax on the right, the nylon insulator is installed correctly.

Ok perfect, thank you!

 

[SouthernRoller]

You need to remove the flat washers on the bottom of the mount. The nylon washer is in the correct position, but there is no need for the flat washers on the bottom. The stud rest flat on the mount. There could be a grounding issue having them flat washers in there.

 

[SouthernRoller]

Here is a video of how it should be assembled.

https://youtu.be/XCffFSJiA8A

Here is also a still image
http://www.walcottradio.com/firestik-m164a-aluminum-mirror-mounting-bracket-p-270.html

 

[MBill]

Tony,

Didn't find a Browning 28, but did find a Browning BR28 on the web. If you have this model, then you
should have a coil mounted about a third of the way up antenna. Looks like it is held in place by
two clamps or screws. Since this is an all metal antenna, looks like you can adjust it by loosening
the coil and moving it up or down a bit. Maybe some one more familiar with this type of antenna can
confirm that is the adjustment. I also agree with Dump Trucker. You could be grounding the antenna by
the metal washer or that metal piece the runs across underneath, touching the center threaded stud
of the antenna, or the antenna threaded mount stud. Those nylon washers have a very small collar on
them and just cover the depth of the mounting hole.

 

[tonylopezx]

Thanks guys for all the input and help. The antenna I have is in fact the BR28 with the coil. I'll go ahead and remove that flat washer on the underside of the mount, the mount kit came with a locking and flat washer as well as the nylon washer, but I'll go ahead and remove those washers underneath. I'll also try to adjust the coil as well, there's two set screws for the actual whip up top, and there is also set screws for the coil itself, I'll go ahead and mess around with it and see if I can get any sort of different SWR reading.
-Tony

 

[SouthernRoller]

I don't think the coil is adjustable on these antennas, just the upper stinger.