I admit it: I need help tuning my CB radio antenna

[TurboMinivan]

I've got an old but reliable Uniden Pro510XL CB radio. I originally installed it in my Shelby Charger; it next saw use in my XJ Cherokee and, eventually, in four of the five TJ Wranglers I have owned (including my current one). In all this time, I have never attempted to tune any of my antennas. In fact, I've never even used a SWR meter.

In addition to the Pro510XL, I am using a Tiger (by Everhardt) 3' fiberglass antenna mounted on a TeraFlex taillight bracket and an 18' coax cable of unknown brand. My CB is powered by plugging into the cigarette lighter (to facilitate quick removal when not in use so as to prevent theft).

Curiosity is finally getting the best of me, so I recently bought an inexpensive yet well-reviewed meter from Amazon (Workman SWR-2T). Today I finally had the chance to use it. I read the directions three times, then followed them perfectly. Let's just say I was less than impressed by the results.

Choking down the embarrassment, here is where I stand:

Ch 40 = 3.5
Ch 20 = 3.25
Ch 1 = 2.25

IIRC, this antenna is supposed to be tunable. But from what I understand, tuning is designed to get channels 1 and 40 more equal to each other; I don't know that it will help lower all three readings. I think something else is at hand here.

So where do I start?

 

[sixstringsteve]

You're right, tuning the antenna will only make ch1 and ch40 similar, it won't lower everything. To lower your SWR number, you'll need a better ground. Make sure the mounting bracket is mounted to bare metal with no paint in between. Electricity doesn't flow through paint very well.

 

[gijohn40]

good call steve! hit it right on the head...

 

[TurboMinivan]

To lower your SWR number, you'll need a better ground.

good call steve! hit it right on the head...

Okay, I'm willing to accept this. From everything I've read on the subject, it seems likely. The TeraFlex bracket has a hole for you to drill into the Jeep's tub and insert a bolt and nut, supposedly to ground the bracket to the body. As Steve mentioned, there is paint involved--both on the bracket and the tub. Rather than stop there, I'm willing to go one step further and add a dedicated ground wire for the antenna. I figure I can take an eyelet, attach it at the right spot* so it is directly contacting the bare metal on the antenna, then route it to where I can make a solid connection to the body/chassis/whatever.

*--now I need to figure out what the right spot is. The antenna came with a plastic spacer/insulator to install between the top side of the mounting bracket and the antenna mast itself and through the hole for the antenna, so I'm guessing that's not where I want. This plastic spacer does not extend below the bracket, and the outside of the lower metal piece makes free contact with the (painted) surface of the bracket... so I'm guessing this would be a good place to insert an eyelet on a wire to send to ground.

Does it sound like I'm on the right track? Do I need to include a photo or two so what I'm saying makes sense?

 

[sixstringsteve]

This is exactly why I always recommend a magnetic mount antenna.

The antenna came with a plastic spacer/insulator to install between the top side of the mounting bracket and the antenna mast itself and through the hole for the antenna, so I'm guessing that's not where I want.

You are correct. The antenna has two wires. One needs up be grounded and the other needs to be isolated. (Hence the plastic isolation ring).

This plastic spacer does not extend below the bracket, and the outside of the lower metal piece makes free contact with the (painted) surface of the bracket...

The lower metal piece needs to make contact with the bare metal of the bracket, otherwise you will have grounding issues. Remove the paint on the bracket right there so it can get a good ground.

I figure I can take an eyelet, attach it at the right spot* so it is directly contacting the bare metal on the antenna, then route it to where I can make a solid connection to the body/chassis/whatever.

Just out of curiosity, why are you doing this? To avoid having to remove a little paint on the inside of the chassis? Don't make a separate ground wire, just ground the bracket. The only way the bracket will be grounded is if it there is zero resistance between the bracket and the jeep tub (i.e. it's touching the bare metal of the tub at some part). There are two ways to do this:

1) grind off the paint between the bracket and your Jeep (a pretty ballsy step, but you'll definitely get a good ground)

or

2) gound a bolt to your jeep, and then ground the bracket through that bolt. (Any paint between metal plates will weaken/destroy the ground). For this to work, the bolt must touch bare metal on the tub, and bare metal on the bracket or it will never ground through the paint.

 

[TurboMinivan]

I wouldn't worry about a separate ground wire, I'd just ground the bracket. You could ground the bracket with the bolt with which it attaches. Make sure the bolt is touching bare metal of the jeep tub, and the bare metal of the bracket.

Okay, I'll remove it and scrape off both painted surfaces it touches, then reinstall it. Maybe I'll even get fancy and add a serrated lock washer on each side--think they might help?

 

[sixstringsteve]

if you remove all the paint properly, you won't need the serrated lock washer. You'll get better contact with the bolt going straight to the metal. The serrated washer will have a smaller surface area between grounded parts, which could possibly lead to a worse ground. Just remove all the paint in that area and you'll be golden. Use sandpaper and clean it well. Report back and let's hear your SWR readout.

 

[MikeGyver]

IIRC, this antenna is supposed to be tunable. But from what I understand, tuning is designed to get channels 1 and 40 more equal to each other; I don't know that it will help lower all three readings. I think something else is at hand here.

So where do I start?

An antenna can only be tuned to one frequency. As you get further from this freq the SWR becomes worse. CBs radios are tuned in the middle of their frequency band on channel 19 so that they use all the channels in the band most effectively... this is why channel 19 are surrounding channels are the most used (by dirty truckers, etc.).

Basically, go to a parking lot, close all the doors etc, and broadcast and adjust the Antenna length until SWR is optimized. Broadcasting with a poor SWR will burn up the radio (over 3 is very bad lol). Once you get down to 1.3 you'll be pretty amazed.

 

[TurboMinivan]

if you remove all the paint properly, you won't need the serrated lock washer. You'll get better contact with the bolt going straight to the metal.

Very well. I'll do this the first chance I get (which may not be for a few days) and report back with the results.

 

[rholbrook]

You're right, tuning the antenna will only make ch1 and ch40 similar, it won't lower everything. To lower your SWR number, you'll need a better ground. Make sure the mounting bracket is mounted to bare metal with no paint in between. Electricity doesn't flow through paint very well.

Before each trip I take a little grinder to my Terafllex mount to clean the rust off. Works great after that

 

[gijohn40]

if you put Noox on there it will never rust... and it helps make a better contact... being an electrician I have abottle if you need some...

 

[rholbrook]

if you put Noox on there it will never rust... and it helps make a better contact... being an electrician I have abottle if you need some...

I may take you up on that before the next trip. Thank you.

 

[gijohn40]

just send me a pm... I'm just down the street from ya!

 

[irish1371]

best bet is to use a continuity meter and see how your ground is holding up before you do the swr. here is a little chart for reference to help out

 

[SAMI]

You oughta PM Hickey on the board. He knows a bit about this shtuff.

 

[TurboMinivan]

UPDATE

best bet is to use a continuity meter and see how your ground is holding up before you do the swr.

Those photos look mighty helpful, thanks.

Today I finally had a chance to improve the TeraFlex bracket's ground connection. I removed the ground bolt, then ground off the powdercoat on the appropriate area of the bracket. Next, I ground off the paint from the corresponding spot on the inside of the tub. Then I put the bolt back in and was giddy with the improvements which were sure to follow.

No dice. My SWR readings are exactly the same as before. This must mean one of a few possibilities:

1) My meter isn't producing correct readings.
2) I am not using my meter correctly.
3) There is another problem somewhere (continuity).

I don't have any sort of continuity test meter, so I'm kinda stuck at this point. I already PMed Steve to see if he'd be kind enough to invite me over and check it out with me.

 

[sixstringsteve]

come on over, I"m free tonight.

 

[irish1371]

gaa if memory servers... swr meter place cb on ch 1 key mic adj meter to the set limit on read out then while still keying mic flip switch to forward. This gets you you swr for ch 1 repeat for ch 40. IF 1 is higher then 40 then ant is too long and if 40 is higher then 1 it is too short.

If you wish to do some good reading go to www.rightchannelradio.com they have a ton of straight forward articles that can get anyone up and running.

If your ground checks out I would look at the cable next. you can't skimp on the antenna wire if you want a top notch cb set up.

 

[Hickey]

I've had a brand new cable give a high SWR before. Try switching out some things to try and identify the culprit.

 

[TurboMinivan]

ANOTHER UPDATE

Since my last post in this thread, I splurged and bought myself a multimeter. I then removed the now-infamous antenna bracket ground bolt and scraped off a little more paint, then verified I had good continuity between the bracket and the tub. I even verified I had good continuity between the coax cable housing and the Jeep's tub. In fact, I found out I have good continuity between the coax cable housing and the inside of the Jeep's tub even with the antenna bracket's ground bolt removed from the vehicle. In other words, I no longer think my problem is being caused by an incorrectly grounded antenna bracket. Despite all this, I'm still getting my high test readings.

I made it over to Steve's house tonight for some additional troubleshooting. The first thing we did was use his SWR meter to see if it would register different readings than my meter. It did not--his readings were virtually identical to my own. We were just about to start fiddling with my antenna's "height" when Steve went into his house and fetched a brand new (still sealed in plastic) magnetic mount antenna. We disconnected my antenna cable from the meter, then connected his shiny new antenna with its own integrated cable. I placed this antenna in the center of my Jeeps' hood, then we took more readings. They were essentially the same as before. This means we had ruled out my meter, antenna and coax cable as possible sources of the problem.

Steve suggested I find a very wide open place and re-test my setup just in case we were getting interference from any nearly buildings. On my way home, I found a nice open spot on a small hill. When I checked my readings (now back to using my own meter), they were still unchanged.

Well, crap. What else is left? I'm gonna have to go back to that Right Channel Radio web page posted above and do some more reading, I suppose.