highoctane

I recently picked up a 102" steel whip antenna from Radio Shack since I broke the last to Firestick and Firefly antennas I had. Initially SWR was off the scale over 3.0. I pretty much new I had a bad coax cable at that point. I went back and picked up a stronger mount(for the longer antenna) and a new 20ft coax from Radio Shack. I wanted to get an 18ft but they had only 12 and 20. I did not coil up the extra tightly, but wound it in a very long oval up the aft end of the roll bar. The entire cable is run down under the roll bar padding, the length of the roll bar, back to the factory sub, then out under the tail gate seal. No sharp bends or kinks. My radio is a cheap Cobra 19 Ultra III that had a 1.3SWR with my 4ft firestick.


Here is how the antenna is mounted.







Afetr doing all this, I retested and my SWR is at 2.1 on ch.1, 2.0 on ch.20, and 1.9 on ch.40. I do not want to trim the antenna to tune SWR, since the instructions say not to, and I was told my the local cb shop not to cut a steel whip antenna, only fiberglass. What else can I do to lower the SWR? Is the receive and transmit range drastically effected by having a 2.0 swr compared to a 1.0-1.5ish SWR?

NQ3X

I'd leave it if I were you. Your SWR readings show the antenna is slightly too short. But it's dashed difficult to add length to a steel whip! Also, if you're using the radio's internal SWR meter, it's probably off.

Modern radios are designed to work into SWR of 2-3:1. Optimal, of course, is 1:1, but that's most often theoretical. What's important is whether or not you're transmitting and receiving signals. I think you'll find decent reception and transmission with your whip, as it is very, very close to a 1/4-wave vertical. SWR with shortened antennas is usually - and deceptively - low, as the antenna itself is a high-Q coil instead of a proper radiator.

The thing to do is get out there and test it. I think it'll work just fine.

Bob

Sahara Lee

The coax, antenna, mount and vehicle all work as a system. To the radio, it's all seen as one entity and any of the four can adversly affect SWR and transmission. Typical SWR should be less than 2 across the board. Close to 3 and you risk damaging your radio.

Take a look at FireStik's knowledge base:
HIGH SWR TROUBLESHOOTING

Entire library is here. You might want to book-mark this one:
Tech-Docs Index

NQ3X

I say again: SWR of 3:1 or lower is JUST FINE. Modern radios have power-reduction circuitry built in to automatically reduce power when SWR climbs above a certain point, usually 3:1.

There's too much obsession with SWR on these boards.

Bob

gunuck

Could nots see in the picture if you have the spring installed under the whip.
Since the antena reads being short the spring will add lenght.
So the SWR should improve.

Cheers.

highoctane

No spring. I heard the spring might help. I've been thinking of getting one so the antenna doesn't bend as much when hitting stuff.

goldtr8

Adding the spring should get you closer.

Sahara_Maverick

And a quick disconnect also adds a bit.

CW Spook

The proper length for a quarter-wavelength CB antenna is 108", which is obtained using the heavy spring with a 102" whip. Here's a quick way to determine the proper length for any frequency:
Frequency Wavelength Calculator

BoneShkr

I have a 108" whip, and a heavy spring from my old YJ.
Where can I mount it on my New JKU?
I was thinking of putting it on top of my rear bumper on
the passengers side, and running the coax through the
bottom of the rear quarter panel of the same side.
No quick connects. This will be a hardened mount. With
the shielding grounded on both ends.