Hello Timon,
Pete's email reminds me of K3NA's excellent eight part series in NCJ
from 2003-2005 describing Yagi performance degradations caused by
multiple Yagis installed on the same tower and on multiple towers.
While many contesters are aware of performance degradations caused
by close spaced Yagis on the same tower, we often forget about
performance degradations caused by Yagis on nearby towers.
Among other things, Eric made us aware of performance degradations
when:
- a Yagi points through a Yagi for the same band on a nearby tower ,
- a 10 meter Yagi points through 15 meter Yagi on a nearby tower,
- a 15 meter Yagi points through a full sized 40 meter Yagi
on a nearby tower.
Eric showed that performance degradations among Yagis installed on
nearby towers is significant when the towers are spaced less than
about five wavelengths apart (350 feet at 14 MHz). According to
Eric's performance modelling, degradation doesn't become
insignificant until tower spacings are greater than about ten
wavelengths (700 feet at 14 MHz).
Multi-band Yagis are much worse, because they cause performance
degradations to Yagis on nearby towers on many bands. I usually
discourage hams from installing them unless thay can be installed
far away from higher performance monoband Yagis.
Some of you have heard me say that a contester can never have too
many antennas... unless (and this is important) they are too close to
each other.
Timon's towers are only one wavelength apart on 40 meters, two
wavelengths apart at 14 MHz and four wavelengths apart on 10 meters.
His Yagis on multiple towers will be much more closely spaced
(especially on 40 and 20 meters) than 40 meters because of their
boom lengths.
My recommendation for his four towers is that he analyze all of the
interactions when each Yagi points through another Yagi on another
tower. His plan to install multi-band Yagis on three of his towers will
surely cause significant degradation of the performance of his high
performance stacked monoband Yagis and he should seriously
reconsider that plan.
The most serious degradation in his proposed antenna system will be
caused by his two 40 meter Yagis that will be spaced much less than
one wavelength apart when boom lengths are taken into consideration.
A better plan is to stack his 40 meter Yagis on the same tower with
each Yagi independently rotatable.
My recommendation is that Timon start with each each of his four towers
dedicated to a single band, this produces the least degradation among
Yagis on multiple towers. After this initial installation is completed,
additional antennas can be added and the resulting performance
degradations can then be evaluated.
73
Frank
W3LPL
----- Original Message -----
From: "Pete Smith N4ZR" <n4zr@contesting.com>
To: cq-contest@contesting.com
Sent: Monday, August 25, 2014 11:47:27 AM
Subject: Re: [CQ-Contest] antenna setup question
K3NA did some sophisticated studies a decade or so agoof the K4JA
multi-tower station, for NCJ. You might be able to find those, Timon,
or get in touch with him.
73, Pete N4ZR
Check out the Reverse Beacon Network at
http://reversebeacon.net,
blog at reversebeacon.blogspot.com.
For spots, please go to your favorite
ARC V6 or VE7CC DX cluster node.
On 8/24/2014 9:40 PM, David Siddall wrote:
> Hi Timon,
>
> With multiple towers available, I would keep my 40 meter antennas off any
> tower with 15 meter antennas -- whether monobander 15's or tribanders. Too
> often 40's disrupt the pattern of the 15's. It seems to be very antenna-
> and spacing- specific, and I am not 100% confidant in modeling for this
> issue.
>
> GL es 73,
>
> Dave K3ZJ
>
>
> On Sun, Aug 24, 2014 at 5:25 PM, Timon Kruijer <Pa1t@xs4all.nl> wrote:
>
>> Hello fellow contesters.
>>
>>
>>
>> I have an antenna setup question.
>>
>>
>>
>> This year (and the next) I am building a new HF station. Next to the house
>> I
>> will have four rotary towers standing in a square which are 40 meters
>> apart.
>> The towers are rotatable and are 25m (83 feet) high from the ground. Every
>> tower will also have a rotor in the top with a 2 meter mast so in total 27
>> meters (90 feet). The towers have rings on 24 meters and on 11 meters (not
>> fixed yet) as they are still lying on the ground.
>>
>> To rotate and calculate the directions for each tower and the top antenna I
>> use Microham Station Master de Luxe.
>>
>> My goal is to have a competitive contest station for SO2R, Multi Singe and
>> Multi-2 use.
>>
>> What would be a good suggestion for the antennas in the four towers?
>>
>> The terrain is flat.
>>
>>
>>
>> The antennas I have available at the moment are:
>>
>> - 2 el Force 12 40 meters
>>
>> - 4 el Steppir 10-15-20 meters
>>
>> - Optibeam 10 15 20 meters
>>
>> - Force 12 c31xr 10 15 20 meters
>>
>> My idea so far is to use these 4 antennas for multipliers etc.
>>
>> I would like to have additional 2 antenna stacks for 20, 15, and 10 meters
>> (which I have to build).
>>
>>
>>
>> A possible setup could be:
>>
>>
>>
>> Rotatable Tower 1
>>
>> top rotatable, Steppir
>>
>> bolted at the tower 20 meter yagi
>>
>> bolted at the tower 20 meter yagi
>>
>>
>>
>> Rotatable Tower 2
>>
>> top rotatable, c31xr
>>
>> bolted at the tower 15 meter yagi
>>
>> bolted at the tower 15 meter yagi
>>
>>
>>
>> Rotatable Tower 3
>>
>> top rotatable, 2el 40m
>>
>> bolted at the tower 10 meter yagi
>>
>> bolted at the tower 10 meter yagi
>>
>>
>>
>> Rotatable Tower 4
>>
>> top rotatable, 3 el 40m
>>
>> bolted at the tower optibeam 10 15 20M
>>
>> bolted at the tower 3 el 40m
>>
>>
>>
>> Or setup 1 multiplier tower and use the others for 10 to 40 meters. Which
>> band to have a double set antennas when this would be a solution?
>>
>> For 40 and 80 meters I will have additional 4 squares behind these towers.
>> Also possible would be to have wire 4 squares hanging on ropes between the
>> towers (between the top rings on 24 meters).
>>
>> For 160 meters the towers can be a 4 square by itself (they are isolated).
>> Also the ropes could be again for a 160 meter antenna.
>>
>>
>>
>> Suggestions and comments are very welcome. Please your ideas.
>>
>>
>>
>> '73 Timon
>>
>> PA1T
>>
>>
>>
>> Home page www.pa1t.com
>>
>> Tel 31 (0)598416308
>>
>> Cell phone 31 (0)657545506
>>
>>
>>
>> _______________________________________________
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>> CQ-Contest@contesting.com
>> http://lists.contesting.com/mailman/listinfo/cq-contest
>>
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