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Old 01-13-2008, 07:34 AM   #1
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Hooked up a CB to the factory Alpine CB antenna and I seem to have little transmit range.

Has anyone used an SWR meter to tune the antenna?

Is it just a matter of adjusting the antenna height?

Appreciate any tips or your experience.
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Old 01-13-2008, 07:34 AM   #2
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Hooked up a CB to the factory Alpine CB antenna and I seem to have little transmit range.

Has anyone used an SWR meter to tune the antenna?

Is it just a matter of adjusting the antenna height?

Appreciate any tips or your experience.
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Old 01-13-2008, 07:59 AM   #3
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I haven't looked at the CB antenna on my Alpine but I can tell you that most antennas have a small amount of adjustment. The next step is to cut off small amounts while somebody watches the swr meter. Obviously, you don't want to cut off too much at once.

Good luck
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Old 01-13-2008, 10:26 AM   #4
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If you have an SWR meter you can easily tune the antenna by following the instructions. If not, try to find a local truck fuel stop and ask then for a nearby CB shop. He can do it and charge you a few $$$.

But do not use it until you get the SWr checked and set. You will burn the final transistors out of the radio.

Ken
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Old 01-13-2008, 10:47 AM   #5
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Interesting, several of us traveled togethter this past year--two 2003s and a 2005 Alpine. The CB on the 2005 (roof mount) worked fine (validated by SW meter). My side mount antenna and my friend's 2003 roof mount had very poor transmition levels. We swaped his radio on to a small mag-whip antenna I had in the truck and pegged the SW meter. I cant find it/prove it but I am convinced WRV installer tightly coiled the excess co-axial cable in some coaches causing a "choke" in the transmit signal. Accordingly, you can trim the antenna all day and it wont help. Can you say FSN radios?
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Old 01-13-2008, 04:52 PM   #6
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Jim&MaryJo:
Hooked up a CB to the factory Alpine CB antenna and I seem to have little transmit range.

Has anyone used an SWR meter to tune the antenna?

Appreciate any tips or your experience. </div></BLOCKQUOTE>

I had a CB specialist try to SWR my antenna because of very short range.
He found the factory antenna had a short = no resistance.
I believe CB antennas require 50 ohms resistance to operate properly?
Anybody know if you can just add a 50 ohm resister to the cable?
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Old 01-13-2008, 06:21 PM   #7
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I'd like to know too (50 ohm resistor??)


There seems to be an abundance of inexpensive ($20-30) SWR meters on ebay. I'm planning to buy one and give it a try.

I have been using the CB and it still works, just short transmit range.

I prefer marine VHF radios among my regular caravan buddies (inland travel), but also use GMRS/FRS. CB can come in handy too. Never have enough comm...
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Old 01-13-2008, 08:57 PM   #8
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I have been wanting to get our antenna tuned. We don't get out very far at all. I have talked a CB shop owner and he thinks he can help us.

When we do use the CB it interfers with the cruise control, slowing our cruise setting. When we use the CB at engine idle speed it will sometimes increase engine RPM
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Old 01-13-2008, 10:05 PM   #9
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I will address this as if I know what I am talking about, (which I don't)
A CB antenna requires a ground plain. The best setup is, for example, mounted to the roof or side of a Steel auto mobile.
In my Boat I used a Marine Antenna. The Marine antenna has a different type of winding that allows it to work without a ground plain. Most Boats are wood and fiberglass.
There is an aluminum bracket mounted on the roof of my 04. This bracket has the CB and Radio Antenna mounted on it. Aluminum will work for the ground plain but not as well.
In this case, size dose matter!
The Cobra CB I installed works ok but I have not tested it for distance.
Years ago I mounted a CB antenna on the spare tire mount on the back of a Bronco II. It was made of aluminum tube. I did use a SWR adjustable tuning box from Radio Shack. It was a big help but the range was still limited.
What I would like to improve, is the Radio reception.
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Old 01-14-2008, 04:13 AM   #10
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The SWR is defined as the ratio of the maximum voltage applied to the minimum vlotage of the standing wave.If the SWR is 1:1 you have an SWR of 1.0 and no reflected power. For most radios you want an SWR of less than 2.0. As you check your SWr on channels 1 and 40, you will find these the high points and some where near channle 19 will be the lowest SWR.

If your SWR is over 2.0, the reflected power from the antenna system will damage the radio.

The grounding of the radio and the ground plane are very important to the radio and ability to transamit. You can get a marine type no-ground plane antenna and it will generally have much better results than a ground plane antenna on an RV unless you can mount the antenna such that you can get a good ground to the RV frame structure.

The higher the SWR reading, the lower the amount of power you have to radiate from the antenna, so with only 5 watts to operate with, you want to get the SWR down to protect the radio and also improve your transmitting power.

An SWR meter is not hard to use provided you have a good antenna system and a properly grounded radio. If you have excess wire coiled under the dash, uncoil it. In a coil it acts as a choke and can have a negative effect on the transmitting signal.

If your radio is noisey, you may want to run a power lead directly from the radio to the battery terminals. Coming through the coach wiring can lead to excessive noise.

Normally do not expect to get more than a few miles from a CB. They are generally a line of sight transmission. If the atomspheric conditions, are right, you can get a reflected wave refered to skip and talk for hundreds of miles.

Ken
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Old 01-14-2008, 05:54 AM   #11
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Thanks for all the responses so far.

I was aware of the groundplane issue, but didn't know how/if WRV mounted the antenna to achieve a ground.

On my 04, I've seen most areas where they might have coiled coax and haven't found any.

Tom and Patty,
I'm wondering whether bad tuning and excess RF energy from the cb cable is affecting certain dash,smartwheel wiring run close to your CB cabling??

Right now, I seem to have much less than 1 mile line of sight range.

Just ordered an SWR meter (~$20 shipped, eBay). Guess I'll give it a go.
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Old 01-14-2008, 08:08 AM   #12
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All,

In response to the question of adding a 50 ohm resistor, you should not do this. Depending on how you attach a resistor, it turns into a "dummy load" and all you are doing is heating up the resistor and not transmitting any signal. A resistor can be used by a CB Shop as a piece of test equipment but is not used for the purpose of enhancing your signal.

The radio is designed to want to "see" a 50 ohm "impedance" (not a 50 ohm resistance). A properly functioning CB antenna will have a 50 ohm impedance assuming good antenna connections to the radio and no shorts in the coax between the antenna and the radio.

Ground plane: the metal plate that WRV put on top of (our) 2004 Alpine serves as the ground plane. That plate is less than 24" x 24" but it's better than nothing for the type of antenna they supplied. When you see the term "ground plane" the meaning is not so much "a good electrical ground" but more that the "antenna is able to radiate it's signal better if it has a ground plane". The signal radiates across the ground plane: if the antenna is mounted towards the rear of an automobile roof and there is more metal area forward of the antenna than there is to the rear of it, the transmit signal will reach farther forward than it will rearward.

Antennas will work best if they are sitting in the middle of a ground plane (usually a piece of metal). But, look at all the truckers with their antennas mounted on their mirror brackets. The point is that most CB installations are less than perfect so don't expect to achieve perfection.

&lt;Ohmmmm&gt; A little bit of electronic humor at the expense of some Zen humor.

Cheers!
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Old 01-14-2008, 09:30 AM   #13
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Thanks Mike!

That is a great explanation.

I'm not expecting much range, but I do hope that when I can see my buddy in the rear view mirror and hear his transmissions, that he will hear mine.
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Old 01-14-2008, 06:06 PM   #14
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On my 2003 Alpine I found that the C/B ant. that WRV installed on the coach has to small of a male end on the cable and it doesn't make contact to the radio.
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