I've got a question about tuning a Cb. I've got one mounted in my Jeep using the Cooltech gate mount and all is well. I've been wanting to purchase an inexpensive swr meter and check it just out of curiosity. Now the question...I know with my firestik, adjustments can be made at the tip to fine tune (lengthen or shorten) but what if you had a different ant that wasn't adjustable at the tip? How would you adjust it if the swr reading were off?

Silly question I'm sure, far from a CB expert here, so excuse my ignorance.

 

You could add a spring to do some corse tuning on a non tunable antenna. Also you can cut the tip and remove some wire from the top of the antenna to shorten it if you need to tune it shorter

 

The first thing to be done is to make sure your coax is cut at a 3 ft incriment. This means that your coax should be 3'-6'-9' etc. a good length for vehicle application is 18 ft for example. If its cut much outside the 3ft realm even a adjustible ant can not be tuned.

 

I'm registering a Pro Forma objection to this incorrect information, as has already been treated in a previous thread.

Phil

 

To the contrary, a very good question!

A pre-tuned antenna is built to a statistical standard electrical length, estimated for the intended customer. For an example, an antenna intended to be used on a big rig may be built to a slightly different length than one intended for a smaller vehicle. Cobra has some info alluding to this**. The point being, if you have a pre tuned antenna, it is not tuned to your exact needs. The problem can best be dealt with by not buying a pre-tuned antenna.

If the antenna is too long, you may remove wire from the top. If the antenna is too short, adding a base spring may get you close enough. Antennas are cheap and a wise man values his time. Buy adjustable.

The antenna tuning point will vary with the location on the vehicle and particularly with the proximity to other objects such as tires, tops, side of vehicle and height of the radiating element above all other obstructions. In short, a non tunable antenna can be tuned by changing its mounting location on the vehicle. How many holes can you tolerate?

Phil


** Antenna manufacturers literature is normally a very poor source of antenna / transmission line theory.