Jim Lux had a number of theoretically interesting comments on the Array
Solutions app note that suggests checking the phase of two antennae using an
oscilloscope. Since I actually used this technique, and wrote about my
experience in another app note on that same site ( "Notes on Stacking an
open sleeve feed antenna and a direct dipole feed mono-bander"
http://www.arraysolutions.com/Products/opensleeve.htm ) I thought I'd weigh
in.
Many of Jim's comments are accurate, but can be dealt with with only a small
amount of effort.
In my case, I asked a ham who was only about 700 yards away to provide the
test signal. I also asked him to run 1500 watts FSK. That gave me a nice
loud signal to play with.
Next, we did this on 10 meters, and we did it at night while the band was
dead. That helped to ensure a nice clean signal.
Finally, I put a fairly high quality 10 meter bandpass filter (that I had
carefully checked for phase distortion using the same dual input 500 mhz
digital 'scope) in the line, which ensured that I wasn't seeing a signal
cluttered up with stuff from other bands.
In fact, the signals coming into the 'scope were crystal clear and clean.
Then I fed the signals from the two antennas into my 'scope, and laid the
two traces on top of each other on the display - not above and below, but
right on top.
It was trivial to see almost any difference using this setup - the human eye
is very good at discerning differences between two curves laid on top of
each other. You don't have to measure the difference, only see if there is
one.
On top of all that, +- 5 degrees is more than good enough for most ham
applications. Stacking gain goes down very slowly as the phase angles
diverge. 10 degrees of error amounts to around .05 db in lost gain - way
below my threshold of pain.
All in all, the technique (suggested by WX0B) worked extremely well. It was
quick, easy, and plenty accurate enough for my purposes.
Best 73 to all,
***dan, K6IF (ex. N6BZA)
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