Re: Re CB

[Tom Mandera <tsm1@domain.elided>]

> >Have you tuned the antenna with an SWR meter?
> 
> My CB has an SWR meter built in but I do not really understand the
> concept. It doesn't seem to do anything noticable.

First,  the internal SWRs are not always the most accurate.. YMMV.

With an SWR meter you hit ch 1 and ch 40, and check your SWRs.. Standing 
Wave Ratio.  What you are measuring is how much signal "goes out" the 
antenna lead, and how much "comes back".  Over 3 is VERY bad (blowing the 
final amplifing transistors in your radio, Bad), while under 2 is OK.  
1:1 is, of course, perfect.

This comes back to the old experiment with your mom's clothesline.  If 
you disconnect one end, and start "whipping" the clothesline up and down, 
you get a wave.  At some point, you get your "wave" balanced out so that 
it is in sync.. that is, you lift your arm and go down, one wave runs 
along the clothesline, hits the end-post, and comes back.  Around this 
time you send another wave, and it hits the first dead on.. in sync.  You 
end up with a stronger wave.

Once you have the sync waves down, jerk yer arm and throw it all out of 
whack.. now your two waves are cancelling each other.. wasting energy.

Same idea on your CB.  You trim your antenna until your SWRs are as low 
as you can get.. when the SWR is 1:1, your "waves" are matching up, 
resulting in the strongest possible transmission signal.. with 3:1 or 
some other larger number, they are effectively canceling each other, and 
your signal is very weak.. you've just wasted most of your signal before 
it ever leaves your antenna.

(It's this continued wasting of the signal and "feedback" that can blow a 
radio's final transistors by making them overheat.. I've had a few radios 
fixed because the previous owners blew the finals)

End of my electronics lecture.. :-)  (shoulda stayed in that EE program.. 
instead of heading for CS)

-Tom Mandera, Helena MT
http://www.tmcom.com/~tsm1/scout
'72 and '77 Scout II
EE Wannabee