CB Antenna tuning / SWR
 

I guess this is the forum to post this.

I just got done installing my CB and Antenna.
Antenna mounted on SmittyBilt XRC tire carrier, and I made sure to dremel the paint off the bottom surface that the stud mounts to in order to get metal-to-metal good grounding.

CB = Uniden 520XL
Antenna = Firefly 4ft.

Bought a sWR meter and followed the instructions for channel 1 and 40.
Channel 1 = 1.25
Channel 40 = 1.4

I think that is about as close as I'm going to get.

Am I done? Is this correct?

Those are excellent but check on channel 19 also to see what your getting on it. I usually tune for it or where your Jeep Club runs most of the time on the trails for the best VSWR ratio, where 19 is where most run on the highways.

Channel 19 was at 1.0 on my meter.
Our local wheelers use channel 22, and it's at 1.0 too.
Probably a little different, but my analog scale needle sits at the same spot.

I think I'm golden with this tune.

Yep. It's so good I'm tempted to think it's not real. Those numbers are in too good to be true territory.

If your line losses are higher than they should be, you can get false good readings.

See how it works in the real world trying to talk to people. If it's really good, then, well, it's really good. If not, you know those numbers aren't real.

Did a range test last night. My buddy has the same Uniden 520XL with a 4ft Firefly, same as my setup. We got 2.43 miles before we started to fade.
This was inner city with buildings etc, all on the same East/West street. I was parked, he moved away from me on his way home.

Local CB shop at the Truck Stop checked, no shorts and everything checked out fine. My buddy's never got that kind of range with anyone he's spoken too in the past on open roads, so he was happy too.

I'm thinking if I can get a good solid mile on the trails then I'll be happy.

I'm going to tune my 3-foot Firefly this week too. It's Parking Garage safe. I'll mount it when i drive to work (2 days a week) and swap to the 4-foot when wheeling.

We also decided to have the CB shop "tune" both radios to somewhere around 10watts. If we need more wattage we'll move to the Cobra 29LX and pump 25w.

Mark is correct the readings are "Almost" to good for a bumper mounted short antenna and it will be more directional because of it.


DON"T let some jackleg at a CB shop twist up the finals in the radio as it will increase distortion in the signal and decrease the life of the radio increased heat in unit for nothing really gained.


But the best reason its illegal to do any mods on a piece of FCC certified radio transmitters unless you hold a license and never to increase the power in a CB as they as limited to class of radio.

Almost a bumper mount. It's mounted the top of the CRC tire carrier which has a grounding strap to the frame. All metal surfaces were ground down to remove paint and primer.

The original numbers before adjusting were channel 1 was 1.0 and 40 was 2.2. Those numbers are acceptable as neither was above 3.0

First I shortened the antenna and 1 was 1.9 and 40 was under 1.5.

Then I lengthened a few turns and got the numbers above.

A check of many CB forums and Right Channel website indicate the numbers around 1.5 (which mine are) is perfectly obtainable on a vehicle regardless of mounting location.

Not arguing, just providing more info from my end/perspective.

I will however recheck tonight and post pics of the meter readings.

as far as modifying any radio-Fred is correct,it is illegal.....many CB shops are just butchers and do not know what they are doing. The "finals" are the transistors. Transistors are rated for x amount of output(wattage) at x amount of volts input (supplied to the transistor). it depends on the radio is engineered as to how to increase output.

Agreed and understood. It was just a thought about having our radios bumped to 10W. Yup it's illegal, but rarely enforced. And it's not like 10W out in the boonies is going to impact somebodies TV.

The CB shop is a pro shop, they do Truckers mostly. When I asked about "tuning" and life expectancy, they informed me they replace the finals with upgraded ones that can handle the heat and thus not much depreciation in life span.

But I'm liking the the clarity and range I'm getting now, may not even want to bump to 10W. If I can get 2.5 miles in the city, I'm thinking a solid half mile to mile in the sticks is perfect.

I'm not worried about the "numbers" I'm getting. Anything below 2.0 and above 1.0 is normal and acceptable.

http://www.rightchannelradios.com/bl...g-instructions

Quote:"Readings on both channels that are less than 2.0 mean that your radio is safe to operate, but transmission may not be optimal."

I don't see anything in my setup or final meter readings that would indicate something is wrong or "too good to be true".

Not trolling, just soliciting feedback ... and for that I thank you all.

even the "pro shops" can be butchers...not saying the one you are dealing with is, but there are many people who bs their way through life. I would be curious to know what he is charging to swap transistors, and what is in there now vs. what he is going to put in. You should be able to spec out the transistors to compare.

I drove a truck for 15 years. I had at least 5 different radios that I can remember, Midland, Cobra's, Galaxy, Ranger, different antennas, amps-had it all...also helped co workers install their radio's . Eventually I started working on my own equipment, finally leaving the trucking industry to go work in electronics full time. Not an expert in radio (or anything else- lol), but I have some knowledge. The best out of the box radio I ever helped install was a small Radio shack that came in a package with a magnet antenna that my uncle had bought. I threw it in my car with the antenna on the trunk and it out performed a stock cobra 29 with a wilson trucker (on a truck). I had someone a few miles away parked at the end of the range and the rat shack was coming in stronger. So you never know.

That's all good, but that wasn't Fred's point. An ideal antenna mount is on a flat surface which extends away from the antenna for at least 1/2 wavelengths in all directions equally.

Anything less than that is less than optimal. The farther you get from that, the farther from optimal you are. Your setup is well executed (workmanship), but a loooong way from ideal, so your numbers are just hard to believe.


1.5 is one thing. Good, but not unusual. 1.2 and 1.0 are in a different world.

However, as I mentioned, the proof is in the radioing, and you seem to be getting excellent results, so if it ain't broke, be very happy with your numbers and happy CBing! :cheers:

Thanks for the feedback all. Agreed on the ground plane. The CB shop explained the theory to me as well and indicated that since my antenna extends almost 3 feet above ny roof that I have a pretty good ground plane, but as you mentioned it not dead center and lop-sided.

I also bough a shorter 2 foot FireStik that is parking garage safe that I can leave on when not in the sticks.

So while I was there he checked continuity on the entire system whiched showed no Opens, Shorts or anything bad.
He then whipped out his $300 digital SWR meter and checked every channel, 1 through 40. The 4-foot was 1.2 on CH-01 and 1.5 on CH-40 and down to 1.0 from CH-06 through roughly CH-22.

The 2-foot Firestik was worse, CH-01 was 2.1, CH-40 was right at 2.1 also. CH-19 was 1.3.

The technician explained that every tune has a sweet spot of at least 10 channel wide, and you can shift that sweet spot higher or lower depending on personal prefs.

Here is a graph of the two which I put into Excel from his printout.

https://cimg0.ibsrv.net/gimg/www.che...c1c76c66a4.jpg

But as BlueRidgeMark stated, the results speak for themselves. Number son paper to me are just that. I'm going to try a 102" whip and see if i can get past 3 miles inner city.

As you can tell, I like to get my head completely around any technology I'm new to, and you all helped me get at least a foot int hat door.

Two Thumbs up!

I'll make one last post as to not wear the subject out.


One: The "Pro Shop" you refer to are nothing but jacklegs period and doubt they even have a license to work on any type of FCC certified equipment. I would never risk my license for doing something so stupid or want to pay the fine of up to $50,000 for the first time your caught. A cheap CB radio is designed around the complete package and any time you change something it affects others and usually not in a good way.


VSWR/Power meters are useful I have a half dozen of them the very best of them are analog/digital meters Bird being what I use for most mobile apps. They range in price from $300-$1k dollars an Alpha Power 2-30 MHz one. Most of the time a cheaper one bought online for a CB works fine for that job and reasonable don't be impressed by someone using a Digital model.


I do use a 102" whip mounted on my rear bumper but you do need to study up on them as they are a different kind of antenna also. I keep mine folded down on a insulated clip on my roof rack when low clearance is needed as you can see here.
Attachment 307463

It's a dead subject Fred ... see my last remark "Agreed and understood." and also "But I'm liking the the clarity and range I'm getting now, may not even want to bump to 10W. If I can get 2.5 miles in the city, I'm thinking a solid half mile to mile in the sticks is perfect."

Let's refrain from calling people names please, especially ones you've never dealt with or met. We can rise above that.

Skill and knowledge impress me, not the tools.


Perhaps I do need to read up on them, because I was under the understanding that each and every antenna has 102 inches of wire. My 2-foot FireStik has 102 inches of wire, so does my 4-foot, and the 102 whip is 12 inches.

In regards to the 102, do you see getting a noticeable improvement on performance over a 4-foot FireStik, or is it just incremental at best?
Also, how did you isolate the whip when you bent it down?

And you did mean bend not folded right? There is no part of the whip that is touching itself?

Thanks again for the feedback and contribution to this subject, it really is appreciated.

The SWR difference is expected, shorter antennas tend to be more narrow banded. I would expect the 102" to have a flatter SWR curve.

I don't know about 3 miles in the city. Environment plays a roll as well so buildings, trees, etc will hinder your signal. A 102" is a great antenna choice, I have always run one on my Jeep and with an old Cobra 19 putting out 2.5 watts could get 10 miles in the open country.