Topband: Re: Pennent Matching

[Tom Rauch]

KV4FZ writes ... 

> The feed point was fed with 300 twin lead (radio shack 
> indoor type) and after 100 feet of twin lead a 50 foot piece
> of RG-8X connects to the Receiver antenna selector switch. I 
> presume that the 100 feet of twin lead  transformer will 
> give me enough of an impedance boost to get close to the 900 
> ohms that is claimed for the pennant.  

Feedlines and how they are attached can change antennas in 
unexpected ways. Mostly because the world isn't perfect.

This is especially true with small antenna that have low levels of 
receive signal sensitivity. 

Signal leakage into a 100 foot long balanced line can easily 
degrade a low sensitivity antenna unless the feedline is carefully 
balanced and almost perfectly installed.

I'd never consider feeding a low sensitivity antenna with a long 
balanced feeder, when a matching transformer with common mode 
isolation through a split primary and secondary winding is so easy 
to do.

BTW, be sure to NOT drop the feedline straight down near the 
antenna, otherwise you will unbalance the system (no matter what 
isolation device you use) and the coax will become part of the 
antenna.

73, Tom W8JI
w8ji@contesting.com


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