Whats a good antenna for a basic cobra 29

Lol, that's what I would think but why do so many people, even antenna manufacturers say to use 15-18' coax whether that entire length is needed or not?

 

I've ask several people the reason and as of yet none have given the reason.

Secondly, the magic 18' would be wrong anyway, because 18' is not the correct length for a 1/2 wave length for 27 Mhz.

Leon
(kc0iv)

 

So why does everyone tell me 18 ft ?

 

It is a myth just like extra channels and export radios it has been told so long to so many that when you question it people will not beleve you ....

A coax does not tune anything and if it does you have a problem .....

 

Some CB shops that repair will tell you it has somthing to do with a "majic number length".
Notice how all manufactures go with 3', 6', 9', 18'. Somthing to do with electrical enginerring formulas or somthing like that?
Have heard it to from only one C.B. repair shop.

 

The "magic number length" is the problem. The engineering formula for 27 Mhz is none of the lengths shown.

Leon
(kc0iv)

 

Simply put, 18 feet is the halfwave length of the CB frequency. But, only when the signal is traveling through air. Your cb frequency is traveling from the radio to the antenna through coax.
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Back in the old days of CB radio, they sold 18 feet of coax because that would allow you to mount your antenna anywhere on your car.
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.The halfwave length of the CB frequency traveling through metal, like the metal wire that is the center conductor of your coax, is actually 11 feet 10 inches. Now that 18 feet of coax will infact work; but, because it is more than 50% longer than the halfwave length of the CB frequency traveling through the coax that you are using --- that proves the halfwave length of the CB frequency does not have anything to do with how long your coax should be. Now aren't you sorry that you asked?
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.And still people believe that 18 feet is a "magical" length. Sheeesh!

 

Learned something new today.. Thanks for taking the time to help us out..

 

Goes to show you can learn alot here by simply paying attention.... this forum is amazing!

 

1/2 wave of ch. 19 (dead center of the cb band @27.185 MHz) is 17' 2.6", so 18ft. still is incorrect.
I remember from 25 years ago during my avionics/radio technician training that CBers used multiples of 3 foot coax sections for some justifiable reason, but I sure can't remember what that reason was, see-ins how it makes no sense, frequency wise...