Huge problem with tuning SWR

**kd123465** · 08-20-2009, 09:46 PM

I unsuccessfully tried to tune my COBRA 75 WX ST CB with a Radio Shack SWR meter. I first placed my antenna on the center of the roof and also tried putting it on the trunk. I kept changing the position and the height, but anytime I got a low SWR reading (about 1.1 or 1.2) I would try to drive the car, and the reading would randomly change. I then found out, even a slight change in position of the coax cable would major changes in SWR reading. Is this normal. Also, I am planning on having a temporary antenna mount, so the coax cables are permanently mounted anywhere. THanks for the help.

**mrcllusb** · 08-21-2009, 08:02 AM

Sounds to me like either you have a faulty coax cable on your antenna,or you have the extra coax just bundled up together..

**srtga** · 08-21-2009, 05:52 PM

Did you set your SWR in an open area with the car doors closed?

**stano0098** · 08-21-2009, 09:03 PM

Originally Posted by srtga

Did you set your SWR in an open area with the car doors closed?

X2

and try to distance yourself from power lines.

**kd123465** · 08-22-2009, 10:50 AM

I think I have the coax cable bundled up, but there is about 10 feet of extra cable. Should I cut and couple the coax even though the antenna box specifically says not to do that?

**chriskohtc** · 08-22-2009, 11:02 AM

DO NOT CUT THE COAXIAL CABLE!!!

Also do not coil the coaxial cable up into a circle. There is an optimum way to coil them up--think its a large figure of 8. But I'm not sure, trying to search online on where I found it.

**voyager7** · 08-22-2009, 03:18 PM

Originally Posted by chriskohtc

DO NOT CUT THE COAXIAL CABLE!!!

Also do not coil the coaxial cable up into a circle. There is an optimum way to coil them up--think its a large figure of 8. But I'm not sure, trying to search online on where I found it.

Ditto.
A large figure 8 is correct.
Also you may have a bad swr meter. I know it's new but that does not mean it can't be bad.

**haansgruber** · 09-01-2009, 02:53 PM

Check the PL-259 coax connector and the coax itself for nicks and cuts. The coax is usually the proper tuned length from the manufacturer. Try to find a way to route the coax in such a way that it is not bundled. Even though it has a shielded braid around the center conductor it still has what is known as skin effect (electrical currents traveling along the outside of the coax). If you loop the coax make sure the loops are not one on top of the other ie: a coil which will have some sort of reactance. Unlike resistance, reactance is undesirable in a circuit. Near field (proximity to each other, in this case coils of coax, can cause them to react to the near field electrical currents of one another) Also; crimping the shape of the round coax can change the impedance.

I hope this helps

haans