[TowerTalk] Hardline ?

[Michael Tope]

Cqtestk4xs at aol.com wrote:

> 
>In a message dated 4/20/2009 10:12:14 PM Greenwich Standard Time,  
>garyschafer at comcast.net writes:
>
>A 1/2  wavelength (or multiple of) of 75 ohm hardline could be used and  
>when
>hooked to a 50 ohm antenna, 50 ohms will be seen at the other end of  the 75
>ohm line.
>
>
>
>That's true, but difficult to do for a tribander.  The 1/2 wave xfrmr  is 
>simple to do for monoband setups, but becomes more complex for triband  
>situations, which is what most guys have.
> 
>73 Bill  KH7XS/K4XS
>  
>

A multiple of a 1/2 wave at 3.55 MHz should cover 20, 17, 15, 12, and 10 
meters (these bands are approximately 4, 5, 6, 7, and 8 harmonics 
respectively).  The greater the multiple, the worse the bandwidth. A 
more bandwidth independent solution would be:

http://www.arraysolutions.com/Products/baluns.htm#50:75%20ohm%20Xfrm  
(see AS-75:50-1)

At $85 a pop this may be the may be the cheapest solution on a "time is 
money basis". It has fewer connections to waterproof than the 
asynchrounous transformer solution and doesn't suffer from the bandwidth 
problems of the multiple of a 1/2 wave line scheme. Which solution is 
best depends on the particular circumstances. It is an interesting 
system design problem.

73, Mike W4EF..........