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Unread 06-10-2013, 08:49 PM   #1
WWheeler
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Is my CB ground good enough?

I have a Uniden 520xl radio, a Wilson Flex 3' antenna, and the teraflex tail light mount on the driver's side. This is my first time installing a CB system on a vehicle. I'm getting 1.5 on ch 1 and 2.0 on ch 40. From what I have read, this isn't bad, but not that good. I am not using that ground wire on the antenna(it raised my SWR when I tried) I know I need to shorten my antenna to get ch 40 down. I've already removed the adjustable tip, so now I will have to start cutting the antenna. Before I do that, I want to make sure there is nothing else I should do. I have continuity in all the right places (and no continuity in the other places), and my equipment all checks out with my multimeter. Could my ground just not be good enough even though I have continuity? I did scuff the powder coating off of the teraflex mount to allow metal to metal contact, but only until I got continuity. Does anyone else have this set up? What readings are you getting?

Thanks in advance!

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Unread 06-10-2013, 09:06 PM   #2
Knuckelhead
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Try checking the SWR in an open and empty parking lot...
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Unread 06-10-2013, 09:12 PM   #3
Jerry Bransford
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Simple continuity is not a good enough ground connection for an antenna mount. Antenna mounts require an "RF ground" which is much more robust and more goes into producing than simply attaching a ground wire. What I do when grounding a mount is to either grind the paint/powder coating away from the two mounting surfaces so both have a bare metal connection, or weld the mount to a suitable well-grounded mounting point. So I would grind all of the paint or powder coating away from the Tera mount so it has more surface area for its ground connection. 1) Make sure the Tera mount gets plenty of bare metal contact at the tub. 2) Make sure to grind away the powder coating on the bottom of the Tera mount so the SO-239 antenna mount's washer & nut have a 360 degree connection with it underneath the Tera mount. Both the Tera mount and the antenna must be very well grounded... an "RF ground" in other words.

Finally, just tune your CB on channel 20... don't worry about tuning it on both 1 and 40, just stay on 20. When you have the lowest possible SWR on 20 which is right in the middle of the CB band, the SWR on 1 & 40 will be as low as possible as well.
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Unread 06-11-2013, 04:55 AM   #4
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With the system together on the vehicle, measure the resistance between the outer shield of the coax and a point on the tub a few feet away. Resistance needs to be below 5 ohms. Lower than 2 ohms is better.
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Unread 06-11-2013, 08:34 AM   #5
Jerry Bransford
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Quote:
Originally Posted by JPNinPA View Post
With the system together on the vehicle, measure the resistance between the outer shield of the coax and a point on the tub a few feet away. Resistance needs to be below 5 ohms. Lower than 2 ohms is better.
Even with lower than 2 ohms there is no guarantee of a good enough RF ground. A simple DC ground from even a 22 gauge wire could easily give that <2 ohm reading but still not be good enough for a good low SWR.
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Unread 06-11-2013, 11:13 AM   #6
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Agree. And you have to give a measurable target. DC is a start, thenSWR.
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Unread 06-13-2013, 10:40 PM   #7
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Not to toot my own horn. But, I've been using and installing CB radios since the mid '70's. Sounds like you've got a good setup. What could be causing the higher SWR is a Hi-Lift jack or a metal gas can near the antenna. You didn't mention how the back of the vehicle is set up. Any metal objects in close proximity to the antenna can drive up the SWR. You might want to go to a longer antenna too. If you look at it, the bulk of the windings are at the top of the antenna. The farther above the top of the vehicle, the better. I use a 5 foot Firestick myself. Also, most fiberglass antennas are designed to be used with a spring. I have about a dozen old broken fiberglass antennas in my garage(don't ask why I haven't thrown them out, I don't know) I've discovered over the years that Firesticks seem to hold up best if you do alot of wheeling. The center shaft is about 3/8" in diameter. The skinnier ones tend to break. Usually the glue joint to the metal base fails. Or the wire breaks. When trimming your antenna, cut about a half inch at a time. If you cut too much, you can always solder a piece of wire back on to it. Checking at channels 1 and 40 will let you know if you're going the right direction. But like the other guy said, do your final check on 20. I run a Ranger 2950DX amatuer radio in my vehicle with a 250 watt amplifier. It's a CB on steroids. When the conditions are right, I can talk to Australia. Alot of the places I go, there is no cell service. With my setup, I'll talk to somebody somewhere if I need help.
Good luck
antenna-mount.jpg   2950-reduced.jpg  
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Unread 06-13-2013, 11:12 PM   #8
xj2k1
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Not to toot my own horn. But, I've been using and installing CB radios since the mid '70's. Sounds like you've got a good setup. What could be causing the higher SWR is a Hi-Lift jack or a metal gas can near the antenna. You didn't mention how the back of the vehicle is set up. Any metal objects in close proximity to the antenna can drive up the SWR. You might want to go to a longer antenna too. If you look at it, the bulk of the windings are at the top of the antenna. The farther above the top of the vehicle, the better. I use a 5 foot Firestick myself. Also, most fiberglass antennas are designed to be used with a spring. I have about a dozen old broken fiberglass antennas in my garage(don't ask why I haven't thrown them out, I don't know) I've discovered over the years that Firesticks seem to hold up best if you do alot of wheeling. The center shaft is about 3/8" in diameter. The skinnier ones tend to break. Usually the glue joint to the metal base fails. Or the wire breaks. When trimming your antenna, cut about a half inch at a time. If you cut too much, you can always solder a piece of wire back on to it. Checking at channels 1 and 40 will let you know if you're going the right direction. But like the other guy said, do your final check on 20. I run a Ranger 2950DX amatuer radio in my vehicle with a 250 watt amplifier. It's a CB on steroids. When the conditions are right, I can talk to Australia. Alot of the places I go, there is no cell service. With my setup, I'll talk to somebody somewhere if I need help.
Good luck
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Unread 06-16-2013, 08:22 AM   #9
MJBinNM
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Quote:
Originally Posted by WWheeler View Post
I have a Uniden 520xl radio, a Wilson Flex 3' antenna, and the teraflex tail light mount on the driver's side. This is my first time installing a CB system on a vehicle. I'm getting 1.5 on ch 1 and 2.0 on ch 40. From what I have read, this isn't bad, but not that good. I am not using that ground wire on the antenna(it raised my SWR when I tried) I know I need to shorten my antenna to get ch 40 down. I've already removed the adjustable tip, so now I will have to start cutting the antenna. Before I do that, I want to make sure there is nothing else I should do. I have continuity in all the right places (and no continuity in the other places), and my equipment all checks out with my multimeter. Could my ground just not be good enough even though I have continuity? I did scuff the powder coating off of the teraflex mount to allow metal to metal contact, but only until I got continuity. Does anyone else have this set up? What readings are you getting?

Thanks in advance!
An SWR of 1.5 to 2.0 is considered good, but you shouldn't have to completely remove the adjuster tip to get there.

I have the same antenna and mount. I had a Uniden 510xl until it died, now I have the Midland CB1 (even smaller than the Unidiens and only 32 bucks from Amazon).

Anyway...I get a pretty flat SWR - 1.3 on Ch1, 1.1 on Ch19 and 1.3 on Ch20. When I installed the mount, I removed the paint from the tub around the 1 hole you have to drill, I also removed the powder coating on the mount at the same location. Removed the powder coating on the mount at the antenna mounting hole. I smeared a little (very little) dielectric grease around those areas just to help prevent corrosion. I clipped that wire off the antenna, as I had no need for it. I also had to shorten the adjustable pin on the antenna, as mine was a little long. Just do it in small increments. Also, make sure you have the rubber cap on when doing your reading.

I was surprised when I replaced the CB that it was still good after 4+ years. I did very little tweaking to the antenna to get from a good SWR reading to a better reading.
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