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CB Radio SWR & Antenna Tune/Tuning

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11 replies to this topic

#1
WilfredA

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Greetings,

I recently picked up a Uniden PRO538W from Fry's for about $50 bucks or so and wanted see if anyone else was having the same results with their setup.

My SWR readings are the following

Channel SWR
1 1.9ish
20 1.3ish
40 1.1ish

I mounted the unit below the steering wheel, above my left knee on the drop-down panel.
Ran the power directly to the battery, and grounded the CB to the metal supports near the fuse box area.
An 18 ft cable runs down, along the door floor sills, under the rear seats, out and wraps around the rear door (didn't drill or funnel through the rear wiper rubber seal yet) to the mount on the rear tire carrier.

Using a cheap 4' non adjustable fiberglass ground antenna from Fry's and initially had readings over 2 closer to 3, for the lower channels until I purchased a antenna spring which brought it down to its current swr levels.

I thought I needed to increase the length, so I purchased a 64" steel whip from Radio Shack and then tested...
All SWR readings were 3+? Was it because it was metallic instead of fiberglass, in combination with being longer?

Also if all readings were 3+, doesn't that indicate a ground fault? Weird because nothing changed besides the antenna and
all grounding should have been the same?

Did the whip antenna change the ground plane and reflect back much more power?

Not sure, so I changed it back to the 4' fiberglass with the spring.

Should I keep the setup as it is now???... Or... get a 5' fiberglass and see if I can get the SWR's lower?

Also, I installed a PA speaker, which emits a loud static noise when the gain is turned up. Is the gain and squelch supposed to be turned all the way down??? When I turn the gain and squelch all the way down, there is no more static... However the sound volume when speaking is not loud at all. When it emits static, it's as loud as an icecream truck on a hot sunny day. But when I depress the microphone and test, the audio emitted is only about 10% as loud as the static????

Sorry for al the babble, but I figured more information the better....

Thanks in advance, and appreciate any help anyone can provide.

Wil
LNDRVR

Edited by WilfredA, 28 April 2011 - 12:45 PM.


#2
HMBRover

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The fiberglass antenna from Fry's (the same one I have) is your best bet. The idea is that the antenna must represent an electrical quarter wave length on the frequency you are operating. That is the lowest SWR point - approximately 1:1. An SWR under 2:1 is generally acceptable. The fiberglass antenna is made up of a wire wrapped around a fiberglass rod. At the low end the wire is kind of a spiral but at the top it becomes a coil. This combination results in an antenna which is in fact an electrical quarter wave on or near the CB frequencies.

But you are right. Your fiberglass antenna is slightly short, indicated by the 1:1 SWR at channel 40 which is the highest frequency (shortest wavelength) end of the CB band. To fix this, I pried the end off the top of the antenna and added about 5 turns of enamel coated wire soldered to the end of the coil there and then re-installed the cap. This brought the resonant frequency of the antenna down to the lower numbered channels. But you don't need to do this, the tuning is "close enough" and the spring you added helps it get there.

An electrical quarter wave on CB channel 7 is about 104 inches. Since the steel whip is only 64 inches, it is way off the electrical quarter wave mark and that's why the SWR is through the roof. It could be made to work with a loading coil at the base, like you see on a trucker's setup. I like the fiberglass antenna better.

A 5 foot fiberglass antenna will be a different spiral/coil configuration but still designed to be an electrical quarter wave on the CB frequencies. It may be a little more efficient but the SWR isn't guaranteed to be better.

Hope this helps ...
Brian
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#3
WilfredA

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HMBRover,

Thanks for the info... It makes a lot more sense to me now that you explained it. Would you believe that i even bought the 2 foot antenna also to test it out! I had a total of 3 antennas at one time, and almost
gave up should I have to relocate and re-wire an additional time. I also figured out that the squelch and gain need to be turned down all the way when I'm testing out the PA system, to eliminate transmission of the static noise...

I've got some returning to do at Fry's and Radio shack, but I can finally put this project to rest without fear of damaging the radio. Thanks Brian!!!!!!! I can now enjoy my CB!

#4
Disco2Guy

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Nice post Brian, it all makes a little more sense now :)

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#5
RON CT110

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Wilfred, something to consider is a firestik antenna; tunable tip. I bought the FL4 (4 feet) for about $18.95 + tax and shipping from GI Joe Electronics: http://gijoesradioel...?idCategory=131

Tread Lightly Trainer: http://www.treadlightly.org/
SPOT Adventures: http://www.spotadven...?trip_id=178167
"Life is not measured by the number of breaths we take but by the moments that take our breath away" - Anonymous


#6
WilfredA

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Hey Ron, do you know of any place locally I can pickup a firestik??? Probably wouldnt hurt to try one out and be able to return it should it not work out... Curious to see how much difference it might make... Truckstops maybe???

#7
NCLR091

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There is a cb store in san leandro on 14th street almost across from Bayfair mall. According to owner only CB store left in Bay Area. Its small not alot of selection but they have firestik 3' and 4'. Your first impression is how the hell does a place like this stay in business. But the owner is very nice and seems to know his stuff(probably happy to have someone walk thru the door) he told me to adjust firestik end about 8 turns and lock it down i have not tried it yet but i'll respond back. I found his card Clydes Corner Electronics 15796 e. 14th st. San leandro (510) 276-8739

#8
WilfredA

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@ NCLR091

Thanks for posting the address & phone for Clyde's. I'm going to drop by this afternoon and check it out....

-Wil

#9
NigelCowan

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Anyone have a SWR Tuner and going to the Annual Event? If so, any chance you could bring it and help me tune my antenna sometime on Saturday?

Thanks,

Nigel
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#10
HMBRover

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I'll be there on Saturday and wii bring the SWR bridge. Look for the orange DII or come to the ham radio forum at 11:00.
Brian
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#11
NigelCowan

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Thanks Brian!
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#12
RON CT110

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Me too; knew Brian would have one. Come see one of us and anyone else who need help; we can help tune Ham, and CB for ch 7. Look for my truck w/the NCLR Ham freq channel.

Tread Lightly Trainer: http://www.treadlightly.org/
SPOT Adventures: http://www.spotadven...?trip_id=178167
"Life is not measured by the number of breaths we take but by the moments that take our breath away" - Anonymous





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