[TowerTalk] Collins vs Modified Lewallen Feed Method

[dan hearn]

Hi Mike: When I lived in Dallas, I used a 4 sq system for about 15 years
on 80 SSB and CW. The first 11 years I used 4 Hytowers with the stubs
removed and a  hybrid coupler phasing system with some success. There
was noticeable deterioration of performance on CW vs SSB where it was
tuned.
  I then did a rebuild. The tubing stingers on the towers were connected
at the top of the towers and extended for resonance at 3650khz. The
measured bandwidth of the verticals was considerably greater with this
change and I used the array for a year in that configuration with
improved results.
  During this time, I used a 4 channel oscilloscope with 4 equal length
coax lines to toroidal sampling transformers at each tower base for
measuring current amplitude and phase in the verticals. I did not find
it possible to get the currents in the 90 deg verticals closer then
15-20% in amplitude and phase to the 0 and 180 deg verticals. IMO the
hybrid coupler ports are not terminated in 50 ohms in the 4 sq and it is
amazing to me that this system works as well as it does. 
  Now, the importand part: I decided to build something to allow me to
set both current and phase for the 90 deg antennas. I built a Lewallen
LC phaser which could be adjusted and a tapped autotransformer (ferrite
core) for amplitude adjustment. With this system, I was able to put the
phase and amplitude to the exact desired values. However, the
adjustments held only over a fairly narrow frequency range. I planned to
build a second unit for CW and relay switch them but personal plans
caused a move to the northwest(Spokane) and the system was dismantled
after a years use. Did this phasing system work well? You bet it did. I
felt that my DX signal was better than with the hybrid coupler. This
system was good for 39z from Dallas and the other one came after the
move to Spokane, Hi.(Tnx, JT1CO),
73, Dan, N5AR 

Mike wrote:
> 
> Hello TowerTalkians,
> 
> Been following the discussion on the K8UR array.  The discussions involved
> the use of a hybrid couple/Collins feed method.
> 
> The plan for 80 meters is to install a phased array from a 125 foot tower
> (with a 2 element shorty 40 meter and a TH7DX on top with all coax lines
> and control wires inside the tower).  Researching the phase shifting
> approach to use and found the Modified Lewallen method doesn't use a dummy
> load hung from one of the hybrid coupler ports as in the Collins Method
> (Antennas and Techniques for Low-Band DXing by John Devoldere, ON4UN).
> 
> For my application, the phase switching point will be 60+ feet up the tower
> which would mean putting up a large dummy load (1500 Watts RTTY is used) at
> that point on the tower.
> 
> So what's electrically wrong with using the Modified Lewallen instead of
> the Collins method?
> 
>         73,
>         Mike, K4GMH
> 
> 
> 
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