Tuning dual antennas...and etc ?'s

"The guy I bought the radio from recommended 18ft cables and I've stuffed the excess under the dash."

what is the radio guide (RG) number of the coaxial cable?

 

Thats excatly what I did to set my dual's just make sure you have a good single coax when you are setting them. mine work perfectly having about 1.5 to 1.7 on each side with a 10 watt dead key 1.3 on the low side dead key

 

You need to handle the excess coax length properly or you can cause yourself a minor problem. Do not make it into a small tight loop. That creates impedence that can throw off your tuning of the antenna.
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It is preferable that you form the excess cable into the shape of a figure "8" that is 10 to 14 inches long. Secure it with tape such as electrical, duct or whatever you have available to prevent damaging the insulation. To bad someone advised you -- incorrectly -- that 18 feet of coax was a good idea. It was not. I suggest coax be 12 feet or shorter to avoid having alot of excess coax to deal with.
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When you compare 18 feet of RG8 and only 12 feet of RG58, the RG8 coax gets 0.12% more signal to the antenna but is twice the price of RG58.

 

"When you compare 18 feet of RG8 and only 12 feet of RG58, the RG8 coax gets 0.12% more signal to the antenna but is twice the price of RG58".

and neither RG type can be used for phasing dual antennas.

 

ALMOST TRUE .....

There are ways to use short lengths of 75 ohm coax and feed them with
RG-58 but it's just as easy to run the RG-59 ....

 

"There are ways to use short lengths of 75 ohm coax and feed them with
RG-58 but it's just as easy to run the RG-59 .

yeah, so?

 

SO ........

It can be done but at 27 mhz is not going to give you any advange .....

On 2, 222 and 440 and up it does .....

 

" Using two identical / properly matched antenna's increases gain by 3 db. "

NOT TRUE ........

Only true if they are stacked ABOVE each other like they do on VHF verticals. Otherwise you get a distorted partern that will show gain and loss ...

Here is a 3 DB Gain antenna stack for horizontal gain .... and 4 stacked for 6 db gain also a 7 db gain vertical antenna using 3 5/8 waves stacked .