Date: Mon, 22 Nov 2010 16:11:07 -0600
From: Larry K4AB <larry.k4ab@gmail.com>
Subject: Re: [TowerTalk] STACKED 40 METER BEAMS MATCH
I use a Stackmatch to feed dissimilar antennas in order to spray RF in two
directions.
For example, during this past Sweepstakes, I fed a tribander at 60' pointed
NW along with a different type of tribander pointing NE.
Both with different types/lengths of feed line.
### Since the 2 x feed lines are different types, and esp lengths,
they will be out of phase, when pointed in the same direction. Since
you have them pointed in different directions.. [ I think this is called
orthogonal, or offset]
its' probably a moot point.
All worked well, but despite claims, the Stack match did not evenly
distribute power to each antenna. In my case, 600 watts to one antenna, and
350 watts to the
other.
### Was each ant 50 ohms and 0 reactance at freq XXX ? If not, that
could easily
account for the 600/350 w split in pwr.
This is probably by design, since I know of no broad banded device (1.8-30
mHz) that can effectively distribute to vastly different loads.
## key word here is... "vastly different loads". I can't see how any broadband
device will evenly distribute power 50-50..to 2 x vastly different loads !
Now if you put 50 ohm dummy loads and wattmeters on each output port,
you will get ur 50-50 split..[ or very close to it]. The 'fix' may be to
install a
simple L network on the ends of each coax.... just prior to plugging the input
ends
of each L network into the stack match. At least that would keep the stack
match happy,
so it 'see's ' 50 ohms + 0 reactance on the output of each of it's ports.
But then if you qsy,
they may each / both have to be re-tuned.
However, the Stack match did keep my amp happy by presenting it with a nice
VSWR.
Someone on this reflector (I forgot who) mentioned that the Stack match has
proven design flaws. Could someone elaborate on them?
## other than the obvious compromise, where the output is designed
for 20 ohms [ sorta mid point between 16.66 and 25 ohms] to handle
2/3 x yagi's... I really don't see anything else obvious. To make a broadband
matching device that handles 40-6m, and 1-2-3-4 x yagi's is tough enough
as is. There may well be some design trade off's, but for the most part, the
basic design is very good. What AS does NOT have control over...is the load
Z
presented to the output ports. When you start installing dissimilar ants,
complete
with dissimilar coax's..and dissimilar lengths, the stack match will see a
real
dogs breakfast on it's output ports. To then expect the power to split 50-50,
may be asking for too much. What does the manual say ?
later... Jim VE7RF
73,
Larry K4AB
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