Cb antenna for dummys!!!

Since this thread is called "CB Antenna for dummies", this dummy has a question, when I changed my Wilson 2000 shaft from the small 5" or whatever small size it is to the new replacement which is 18" shaft, will it effect of change my SWR? It's on a 379 (avatar pictured). I figure someone on here has changed to a taller shaft at one time and if it effected anything.

 

Yes it will effect your SWR. You will have to trim the whip.

 

When I do the switch to the longer shaft, how long can I use the radio before I get the SWR tuned in?

 

i personaly wouldn't use the radio before the SWR would be check again.

 

I never use a radio until I've checked the SWR!!

 

smart man

 

Not as much as you might think

 

Widely believed, but inherently incorrect. First off, a resonant dipole, high enough (in wavelength fractions) above a decenrt earth ground, has an impedance of about 72 ohms. Conversely, a resonant vertical element over an *adequate* counterpoise has an impedance of about 33 ohms. Note that both "perfect" antennas have an SWR of about 1.5:1.
In neither case does the half connected to the coax shield provide a reflection surface from which RF will bounce skyward. In both cases, the major portion of the signal goes toward the horizon, or 15--30 degrees upward from parallel to the ground.

Some NGP antennas use a measured section of the coax from the feedpoint back towards the radio (delineated by a wound trap to set its length) as a way to set the impedance to something the radio will see as an acceptable value. Some others, most notably Fibreglas° marine styles, are actually hollow forms with the coax going halfway up inside,. There, each side of the coax feeds one end of a helically wound vertical dipole -- one going up, one down -- to achieve a NGP antenna independent of coax length. The windings affect the potential range downward somewhat, but having the whole thing a few feet above a vast watery ground plane still works better than the whole array over pavement or a rocky mountain trail somewhere.

HTH,
73

 

I didn't respond because I didn't see it. I don't subscribe to threads so I don't know what's going on until I read it.

But that said the problems related to straps or wiring (straps prevent parasitic non-resonance emissions aka static creation) in the system is to provide continuity for an rf ground but doesn't always need to be so large that it handles a lot of current. The current can be mitigated with proper tuning of the ground system itself - which means for the most part having equal "close to frequency" resonance on both parts of the antenna so the strap handles an equal amount of current.

However if we are talking about the entire system from power to rf, then a large wire (strap) would be needed to handle the entire system current, a good example is an isolated commercial two way system.