SWR Tuning Advice

[NYRHKY94]

Hi Guys:

Looking for some advice/feedback on an SWR tuning issue I'm currently having. I'm seeing a very wide SWR reading swing between channels on my Uniden CB. On channel 1, I have an SWR of approximately 1.1. On channel 19 it's approximately 2.1 and on channel 40 it's over 3. No matter how much I raise/lower the anetnna whip, I just can't seem to get a consistent 1 to 1.5 SWR across all the channels as recommended. I'm using a brand new SWR Micronta meter for the SWR tuning.

Any suggestions on what I'm doing wrong or whether I might have an issue with the CB or antenna?

Thanks in advance!

 

[rfradioconsult]

What length of cable you are using between your radio and SWR meter?

 

[NYRHKY94]

The cable length is the one that came with the antenna (Liliitle Wilson magnet mount). It's approximately 15' long with a standard PL259 on the end.

 

[rfradioconsult]

What length is the jumper you are using between the radio AND your SWR meter; not the coax length to the antenna.

 

[NYRHKY94]

Sorry about that (need to read more closely). The "jumper" cable between the radio and the SWR meter is only 2' long.

 

[rfradioconsult]

Describe how you have the antenna mounted.

 

[NYRHKY94]

It's a Little Wilson "magnet" mount on the trunk.

 

[Highlander_821]

The length of coax and jumpers should not matter. Based on the curve you are getting, you need to shorten the antenna to bring it close to resonance at channel 20. Try adjusting it as short as you can get it, and post the new results. You might actually have to trim the whip a little if you are still showing long. But you shouldn't have to.

 

[kb2vxa]

It's unlikely you'll get a "flat" SWR reading across the board, the important thing is to get it as low as possible in the center of the band. Lengthening the whip lowers it on lower channels and shortening it makes it lower on he higher ones so with that in mind you know whether to make it longer or shorter, check it on the band edges and shoot for lowest the middle.

You may have to snap off a bit of rod from the bottom end, cut a groove with a hacksaw or file and snap it with two pair of pliers. Just a LITTLE at a time, no more than say about a quarter of an inch, if you make it too short you're screwed.

It doesn't matter how long the jumper between the radio and the meter is, both will be removed when you're finished so when you connect the coax directly the reading you got is what the transmitter will see.

 

[rfradioconsult]

Before performing major surgery on your antenna; if possible temporarly set the antenna in the middle of the roof with no large metallic objects nearby, then re-check your SWR. The easiest way to trim the whip is nick it with a file or a bench grinder then snap it with a pair of pliers; a hacksaw will not nick the whip.

 

[JayMojave]

Hello NYRHK94:

These little Will Wilson Antennas are a very short antenna meaning they will not have a very useable bandwidth. The SWR measurements sound about normal for that type of antenna. I have taken those antennas apart only to throw them in the trash. But they will work for a shorter low performance antenna. But the Wilson 1000 or 5000 is a much better antennas.

Coax length will show different SWR measurements when the antenna design is allowed to radiated RF Energy down the coax. This is seen many times in mobile antenna installations when not enough ground plane is used.

I'd say what you have is what you have the top whip length adjustments to the Little Will Antenna will show insignificant changes in SWR and performance.

Hope this helps.


Jay in the Mojave

 

[NYRHKY94]

Guys:

Thanks to all for their feedback & advice! This site has so many helpful folks on it. I did move the Little Wilson Mag Mount around to different locations on the trunk (my preferred set-up) and sure enough there was a difference in SWR readings. By moving the antenna about 3" back from the upper trunk lip (centered near the back window), my SWR readings on both channel 1 & channel 20 were in the 1.2 range. Channel 40 was still high at 2.7 or so. Acceptable for my minimal use (i.e. traffic reports).

P.S. I took the plunge on a Wilson 1000 a couple days ago and it should arrive today. I also purchased the Wilson short load replacement whip to go along with it, as I do have a height issue with the garage. Once I have the 1000 installed, I'll take some SWR readings with both the 62" whip and short load and see what I get.

Thanks again guys!

 

[Highlander_821]

Good move on the Wilson 1000. I have one and love it. It works very nicely as a 10 meter antenna, too.

 

[ERICMYERS]

super basic concept, but not addressed yet.

calibrate out in the open, like the middle of a large parking lot, not in the garage.
Eric

 

[rescuecomm]

I use a small set of bolt cutters to trim antenna whips. Just remember everyone around needs safety glasses on when you cut. The small piece becomes a fierce ballistic.

Bob