[UK-CONTEST] OT but Likely I'll get answer....

[Adrian Rees]

Hi all
Thanks to those that replied (on and off list).Most of the mail I have read, one or two I havn't as I didn't get time before I left for the office this morning.
 
Just to clarify a few things, as I may have added to the confusion :)
 
I am installing a number of towers in a field. Each of the towers is spaced around 40 m from each other in a square formation. (No guesses whats going on here...eventually!). 
 
The distance from the shack to the tower bases, varies between 40 and 100m. Height of these four towers is 20 -25m. In addition I will be installing a further two towers, at a distance of  nearly 350m from the shack.
 
Minimum feeder cable run is therefore 60m, maximum 375m.
 
Each tower will support mono band HF yagi's.
 
The fundamental problem is location of the shack, in relation to the towers. ie, 240V mains feed to a shack located close to the Towers will be very costly in terms of cable and installation. Furthermore it will also necessitate installing a seperate shack !
 
So, I plan on using a building that already exists, with plenty of 240V Power (in fact 3 Phase as it was once a dairy).   
 
Back to the original problem: Feeding 4 - 6 Towers with Coax will be costly, in terms of actual cable, and loss. (At 14MHz, RG213 over a run of 300m has loss, with connectors) of 7dB or more. This equates to 100W in, 18W out....not accetable!).
 
So the thinking is, install 9:1 TLT type Baluns at each end of a length of 450 Ohm Open Wire Feeder. Connect RG213 (in lengths no longer than say 5 or 6 meters) to the Baluns and connect the RG213 to Radio and Aerial. This would, in theory, produce a loss of around 1.15dB. Which is much more acceptable.
 
So far the experiments I have carried out, support the theory. 
But, I want to achieve an efficient match as possible (lowest loss) and length of the Open Wire Feeder can cause impedance variances depending upon Frequency / Length. What I want to do is install the Open Wire Feeders, measure the impedance presented, and build the matching TLT Balun.
 
Making the Open Wire Feeders isn't a problem (plan on using 1.5mm solid core insulated wire and 3 - 4" Spreaders. This will be supported on 6 - 8 Foot Posts, cross arm and Ceramic / Glass insulators. (The insulators came from a job lot of ex Scottish Power 11Kv Line Insulators...have enough of them!).
 
Thanks All
 
Adrian