CB Antenna & SWR

[OSP1268]

I am not an avid CB'er. I just like to put it on, especially when on the freeway. I have found that it is useful for backups and constructions zones so one knows what lane to be in.
Anyway, I have been trying to get a decent SWR match between the radio and the antenna.
First I put on a 2' Firestick antenna and checked the SWR. It was 8:1 on channel 1 and 10:1 on channel 40, and 19 was 8:1 also.
So I thought something was not connected somewhere between the radio and the antenna, or possibly a dead short
in the cable somewhere. This morning I took the entire assembly off the roof. The cable is good, no shorts or problems there. I checked
with a meter to be sure.
Someone earlier suggested that I put a couple of strips of the metal, (silver) tape on the roof and that would give me a good ground
plane, thus improving the SWR. I did that and I still have the same SWR that I started with.
So I am open to suggestions or ideas. Or do I have to live with it the way it is?

[GaryKD]

Hi OSP1268,
Did you install the antenna and antenna wire? If so, did you install a ground plane or no ground plane antenna/wire system? Is the antenna top, middle or bottom loaded?

[OSP1268]

Quote:

Originally Posted by GaryKD Hi OSP1268, Did you install the antenna and antenna wire? If so, did you install a ground plane or no ground plane antenna/wire system? Is the antenna top, middle or bottom loaded?

The antenna is a 2' Firestick. The antenna wire was all ready installed, but checks out okay. The antenna is on top of the motor home. Supposedly there is a metal plate under the fiberglass roof, but I wonder about that. I have checked with other Allegro owners and they seem to be able to get a good SWR match. Or at least within a reasonable range.

It is not a ground plane antenna. But no one else that has the identical model as ours seems to be having this problem.

[wa8yxm]

As I recall the firstick has some adjustment, 10 to one on 40 but only 8 to one on 1 indicates the antenna is too short.. Lengthen it, Then re-test.

[GaryKD]

Hi OSP1268,
For a coach, what one needs is a top loaded, no ground plane antenna and wire. They are sold as a kit from Firestik at Firestik Antenna Company Home Page . Do not try to mix one kind of antenna (ground or no ground plane) with a different (opposite plane of the antenna) wire. It doesn't work very well.

Many Firestik antennas have a metal screw at the top of the antenna (under a plastic hood). The screw is used to make the SWR adjustment.

If you'd like to see my install, go to CB Antenna - 3' Firestick No Ground Plane Needed - iRV2.com RV Photo Gallery. If one installs the antenna on the side of the coach, a minimum of 2/3s of the antenna needs to be above the roof line.

Manufacturers usually install a ground plane system. They do not install a large enough ground plane. That is why owners have concerns about their factory installed CB antenna system.

[Wayne M]

Where are you measuring the SWR, at the antenna, or at the radio. It will make a difference. At the antenna is the best. However, the coax will also create an swr based on it's wavelength. If I remember the formula, it is 468 divided by the frequency in MHZ times .05 for error. Then any multiple of that number can be used. Measure the length of the cable. I'll wager it is close to 19 feet. Soldering a connector is a tedious task if you have never done it. It is easy to short the coax.

Good luck.

[justimagination]

............Firestik 3' NGP antenna, a M-2 side mount(forget the roof idea). Just call Firestik and tell them what you want. Very simple to install, coax all hooks up inside. You will see this same system on a lot of truckers with fiberglass cab, good luck and travel safe.
David G.

[whem2fish]

i run the firestic mounted on the mirror since rv is fiberglass i do not have a good ground plane (bought at camping world) as above do not mis wrong cables you need below 1.5 to 1 i was able to get 1.3 anything over 2 will burn finals

[Wayne M]

Looking at your original post again, those are very high numbers considering.

Some considerations. Some antennas use the coax as a ground plane. Therefore your radio as to be well grounded. You can also run a separate ground wire from the antenna to a good known ground. As mentioned, some of the Firesticks have a tunning screw at the tip. Just remove the rubber cover and make small adjustments. If you reach the limit of the screw, just go pick up a 1/4x20 longer bolt and try again. You may not be able to get the rubber cap back on but it is not a big deal. You can always use non-conductive RTV silicone

There is antenna theory and there is reality. Even in the best of circumstances an antenna constructed entirely with antenna theory may be the worst antenna one can use. The key word is "theory." It is what is supposed to work under ideal conditions, in a laboratory.

In reality, I have skinned a piece of 30 foot or so RG-8 where the phoenelic (sp) was 108 inches long (1/2 wave length for cb). Pulled all the shielded strands down the rubber insulation. Tied a string to the end and hoisted into a tree. I talked all around the area I was in, and on many a day, depending on skip, to places in the US. I have also worked a CB with 19" of coat hanger sticking out the back, but not recommended. I did have an antenna tuner in place on that one.

The SWR is a measurement of the antenna line, and as I stated, should be measured at the antenna. Placing an swr meter at the radio will show you a low swr, but the swr along the antenna cable will still be as high as originally (or close) and could impede performance. Another way to check is with an RF Field Strength meter. Most HAMS will have one. It will give a good indication of your output and pattern of radiation. If your major lobe is going straight out the side, well, you'll be talking to truckers as the come up alongside of you, but not to far as they get in front of you.

Good luck.

[bigdale]

I believe that you do not have the proper ground to your antenna. As far off as the SWR are you cannot adjust the tip to get the SWR down. Most likely you need to run a ground wire from the ground of the antenna (mount) to a good ground on the frame. Clean the frame where you are gonna mount the ground wire with a file or etc to bare metal. You may also have a bad antenna those little short or long fiberglass sticks are notorious for being bad out of the package. I have used CB's on my bigtruck for 35 yrs, and I also am a licensed amateur radio operator. The biggest problems usually is a bad ground, or the antenna is mounted to close to something made of metal. Good Luck!
oop's I did not see the last post.

[wa8yxm]

The readings indicte the SWR goes up as the frequency goes up.. This indictes an antenna that is.. (I realize now) too LONG, it needs to be shortened.. There is an adjustment for this.

A real expert could likely tell you how much

That said... all the other statements I'v read are true with one possible exception and since it's only possible.. it might well be too. Coax condition and length play a part.

just because a coax is new does not mean it's good.. I know a radio shop (Motorola) which ordered eight factory made jumpers and out of the 8 jumpers they only had sixteen shorts. Both ends on every cable were shorted. Think about this.

[OSP1268]

GOT IT!!!!!!!!!!
Someone told me to go to rightchanelradios.com and try some of their help suggestions. A good web site for checking what you are doing right or wrong with your CB radio and antenna.
Here was my problem. I unbolted the antenna assembly (again) from the roof and hidden within the caulking(sealing putty) was a small connector that the screw that holds the antenna assembly down went through. that connector was nearly completely covered with calking, so it was not making a good, or any, contact. I scraped all the calking off the connector, and off the bottom of the plate that holds the antenna to the roof. That connector goes to the metal ground plate that is somewhere under the roof. I then re-screwed the antenna assembly back to the roof and checked the SWR. I could not believe the results. After some very minor adjustments I have 1:5 on channel 1:1 on 19 and 1.6: on 40.
I would like to thank everyone for their help and suggestions. What a great web site this is..

[wa8yxm]

Well, 1:5 and 1:6 are not good, but that is what you get for a short antenna (less than 9 feet) limited bandwidth,, Since you will normally park it on 19, and never go farether than 17 or 21.. You are good.. You might want to check chan 9,, just in cuss, some places it still is used for emergency.. Actually I'd ch3eck 8, not 9,, one channel not much change but you are still way too high on the ends of the band.

I can't help you there, I use a longer antenna, more bandwidth

(I also have a "Stubby" but I only use it on chan 13, it is actually on a tool box in the basement)

[Wayne M]

Considering that you are using a frequency spectrum of 26.965 Mhz for Channel 1, and 27.405 mhz for channel 40, it will be near impossible to get a flat SWR across the CB frequency spectrum. I'm assuming that Channel 19 will be your primary channel, and an SWR of 1:1 is exceptional for that frequency. An SWR of 1.5 on the low end, and 1.6 on the high end is acceptable. Yes, you will loose a little power, but you will still be within operating guidelines of your receiver. A problem exists with possible damage to finals when the SWR reaches 3:1 or better, so even an SWR of 2:1 will not cause you much problems.

Since most of us are running the CB's to stay in touch with someone who is 1/4 mile or less away, you would not have any problem on any of the channels in that scenario. In my case, if I were to have an emergency I'd use my Cell Phone, but should the need arise to use the CB, any passerby would do to relay my plight.

Glad you got it resolved.

In the days when a license was required to operate a CB my call sign was KDQ8400. That takes me back to the 60's. Twenty three years in military communications, I can tell some stories regarding antenna theory and reality. Twenty six years as an Advanced Class Radio Amateur. Call signs: WB4FVA; KA5KJD, and presently KE5QG

When conditions are right, you can communicate around the world with 1 watt and a wet string.

Happy trails.