[TowerTalk] Upside down and 3 high stacks

[k3lr]

In the wireless telephone industry we mount antennas "upside down"
on a regular basis. 10 years ago you had to order the antenna
for "inverted" mount. Which as Rus NJ2L pointed out, allows 
water to come out of the upside down antenna. Other than that 
mechanical issue, the antennas are the same. Most manufacturs 
have gone to the "remove and install" the plug method now
so that the antenna can be mounted either way. 
It is common to mount cell site omni-directional receive 
antennas inverted.  
 
On another topic:
 
Look for an upcoming antenna article in CQ-CONTEST Magazine
which will detail my switching and matching design for
"3 high" monoband stacks. This method allows 7 combinations 
of 3 monoband antennas with correct matching transformers 
(coaxial lines) for 2 or 3 antennas in phase. 
 
The selections are: 
1) top only 
2) mid only
3) bottom only
4) all 3 fed in phase
5) top 2 fed in phase
6) bottom 2 fed in phase
7) top and bottom fed in phase
 
It provides for a low impedance at the antenna terminals 
when 1 or 2 of the antennas is not being fed. It uses the 
proven current forcing method. It does not change the electrical 
length of the feedline from the switch box to the transmitter 
output regardless of what combination is chosen.
It is a single band solution, but the method can be applied to
a multi-band design using W2FMI UN-UN broadband transformers. 
 
My boxes use 7 SPDT relays and 10 SO239 connectors (UHF females). 
I am not an N-connector fan on coaxial cable if the center 
pin of the male connector is not captivated. 
I have witnessed several instances where the N-connector 
center pin will drift out of the female connector. If the 
N-connector is captivated (held in place by the connector 
body) or we are talking about hardline connectors, 
I am a big N-connector fan.
 
The switch box uses 6 wire control. It is fed with a matrix
box designed by W3YQ and will not hot switch.
 
We have used these "3 high" boxes on 20, 15 and 10 meters 
for 5 years. The contest men that have used the 3 high 
switches at K3LR have found them to be reliable. They have 
also commented that using "all 3" is almost always the 
best combination when all 3 antennas are aligned at the 
target area or station.
 
All 3 antennas in each stack are mounted on the same 
tower and have independant rotors.
 
I have run models with out of phase combinations, however
I do not think the additional switching hardware is 
worth the angle/gain diversity that would be available for
the antennas, spacings and heights I currently have. 
 
I hope you will find the future article in CQ-Contest
magazine interesting.
 
73!
Tim K3LR
 
K3LR@contesting.com

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