[UK-CONTEST] OT But maybe of interest

[Adrian Rees (MW1LCR)]

Hi all
As some of you are aware, I have been conductng (pun not intended!) some
experiments using Open Wire feeder systems to counter Transmission line
loss from (what will be) my shack and Monoband Yagi's.

Some of you wanted to know the results of this, and here's some basic
measurements, carried out yesterday, in between chain sawing fallen
trees!

Using a homebrew 28MHz Monobander (3 Elements) with a measured feed
impedance of (R +/- jX Ohms)27.02 + j 0.50, feeding with 347.85 m (70
Half Wavelengths at 28.5MHz x 99.7% Velocity Factor) of 450 Ohm Ladder
line, with 100w in, gave 61 Watts out. A loss of 1.7dB, or thereabouts.

(The feeder was trimmed to present the same impedance  at the aerial
feed point at the shack end. Therefore on the measurement freq, 28.5Mhz,
the actual feeder length was a multiple half wavelength. This was
matched through a 2:1 Balun). 

The same Yagi, when fed with a length of RG213 (350m), with 100w in,
resulted in 5.4 watts out. A loss of 12.7 dB, or thereabouts.

I plan on conducting similar experiments with 50MHz and 144MHz Yagi's,
just to gain (pun not intended!) more insight into this feeder
mechanism, as I want to feed all my aerials with Open Wire feeder. 

I would appreciate comments on the following:

1. What would be the most efficient method of matching the Open Wire
Feeder, such that the shack end sees 50 Ohms ? (Could be matched at the
aerial or shack end ?).

2. Any ideas how I get open wire feeder around the rotator ?


Thanks
Adrian 
MW1LCR



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