Not as elegant nor as good like the ones exposed before but this is a poor
man's, or emergency, stack match.
Needed:
Two antenna selector switches with two antenna ports
One antenna switch with three antenna ports.
One antenna tuner with bypass switch or a 2:1 unun or a fixed matching network
that brings the 25 ohms to 50 ohms or 37 to 75 ohms if needed or a Q-line
transformer
Equal lenght lines come from the antennas and each line arrives to the input
(common) ports of each the two-antenna port selectors.
Then connect from, say, antenna port #1 of each of the two-anntenna switches,
coax jumpers of equal lenghts that will go to each of the sides a "T"
connector. The third or common port of the "T" junction connects with the
middle position of the three-antenna selector switch. (Could be logical to
connect to position number one, so when BOP is wanted, all selectors go to #1
position and the matcher in line, but it may be worth to check the simmetry and
the paths of the selectors for phasing's sake. Better keep simmetry and
color-code the positions)
The remaining two ports of the three-antenna selector connect with equal
lenghts of coax to the antenna ports #2 of each of the two-antenna selector.
I.E.: Position A of the three port switch goes to the selector of the upper
antenna. Pos C goes to the lower antenna selector and B in the middle is left
for "Both"
The input of the three-antenna selector goes to an antenna tuner with bypass
capability. OR: Instead of the matcher, a 2:1 unun or a fixed network matching
device or a quarter wave transformer line of the proper impedance (SQUARE ROOT
OF 25 times 50) can be inserted between the common of the "T" junction and the
port B of the three position switch. NOTE: You can insert the matcher here too,
specially if it is one of the always-on-line-tune.
For BIP : Select the middle position (B) of the three-port switch and select
port #1 on each of the two-port switches. The matcher must be in-line to take
care of the 25 to 50 ohm transition.
Upper: The three-port switch selects the position that goes to the port #2 of
the two-port selector linked to the upper antenna. And, of course, select port
#2 on that switch! Select the bypass in the matcher if used.
Lower: Same as upper with the corresponding two port selector and the
corresponding port at the three-port switch. Select the bypass in the matcher
if used.When selecting a single antenna, the other two-port switch can be left
in any position.
WARNING!!!!!: It is very easy to get the wrong switching and pour all your
power in to a dead end! That is a no-no, specially if your amp has no
protection for that mishap. Better if done with coax relays or in line relays
with foolproof selection, but to do this I would rather get or clone a stack
match.This is an emergency solution. Positions can be color coded, one color
mark near the right selectors position's for each of the antenna combinations,
. Not the best choice for a long term usage of after 40 hours of contesting on
a Sunday's afternoon. But it can do the trick while in a hurry.
Some antenna tuners are easy to modify to form part of a better version of this
bad idea :o)
BTW: There was an interesting article about phasing with quarterwave lines
combinations, I think it was written by K1EA for The DX Magazine around 1990.
If anybody here knows the issue number I would appreciate to know. I have
looked for this article in my colection with no success.
73
David
HK1A
EC5KXA
ex-HK1KXA
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