[SCCC] SCCC Digest, Vol 88, Issue 7

Fri Apr 9 15:03:50 PDT 2010

Hi Tim

I agree with Glenn on just about everything he said. I have an LM-470 with a
KT36XA 12 feet above the top of the tower at 82 feet and a KT34XA on a TIC
ring at the top of the third section at 54 feet when the tower is cranked
up. I normally keep the tower double overlapped for safety sake. I also had
a 2 element 40M KLM at the top of the tower (which I sorely miss and need to
get off my butt and put back up). I use a WX0B stack match with the
auxiliary function that switches out one antenna to another radio or in my
case into a WX0B Six Pack antenna switch. The six pack allows two radios to
connect to any of six antennas not in use by the other radio. From my
experience there is no benefit in staking gain at this height, at least for
low elevation angles. The patterns in elevation are not the same and the
lower antenna does not add any significant gain. That said, what benefit may
exist is that when in the stacked mode the elevation lobe is wider but the
gain would be better by flipping to either upper or lower. I have not really
seen any benefit between the two combined and the higher antenna in local
contests or DX. I am a flatlander and in a hill top or hill side environment
it may be siginificantly different due to ground gain and the lower
elevation angles. Dave Lawsons book on yagi design concurs with the stacking
gain. The one benefit I have found with the lower antenna is on 10 meters to
the Carribean. This is the only instance where I can flip between antennas
and tell that the lower is significantly better than the upper. I would say
that possibly for local contests the same is true however I do not raise my
tower in local contests so the upper antenna is at 62 feet and the lower is
at 30 feet. I just leave the lower antenna pointed East. In fact in most
contests I use the lower antenna for South America and the Caribbean. Maybe
when conditions improve it will be more useful towards Europe, Africa, and
Asia. It is better than working South America off the back of the upper beam
when pointed at Asia. I do use it to radiate in two directions with the
Stack Match. Again maybe on 15 and 10 it would be more useful as activity
picks up but on 20 the benefit given the amount of hardware in the sky is
questionable. I have had it up through one solar cycle and it is even more
frustrating when you can hear a station but not crack the pile up on the
lower antenna. There are a lot more instances of that at the solar peak. It
does look impressive!

As an aside N6CA and I have ran many simulations on 6 meters for stacking
gain and it seems the lower antenna has to be above 90 feet to obtain good
pattern addition at low angles. The issue on 6 is the lower the take off
angle the earlier the opening and the longer the opening stays in. Also the
difference between an antenna at 50 feet and 86 feet where my is enormous. I
hear people say you only need a 6 Meter yagi at 35 feet to work DX. That is
true but you will not hear what others hear at 70 or 80 feet. It is as
different as night and day. This can be applied to the higher bands. If you
can get in and work stations before others then you are free to work more of
the ones everybody hears. So the lower antenna can be the work horse when
the band is open even though signals are lower, and the upper antenna can be
used as a band opener and closer as well as for long haul and another
direction. In experience even with the close in stations I call several
times on the lower, I give up, swing the upper antenna and work the station
with one call. If I were operating SOHP it may be different. I operate SOLP.
In SO2R the lower antenna is more than adequate for S&P and since I am using
a tribander if I do hear a pile up I can not crack I just swap antennas. 

Finally, Marty, N6VI, had some very intriguing ideas regarding building a
multiplexer filter and reusing the two triband antennas on two radios. That
would allow two independent stations to use both antennas without conflict.
Of course I would only do that with 100 watts! No telling what would blow up
with two 1500 watt stations transmitting. The peak voltages would be four
times that of a single station and that would probably be too high for most
dielectric breakdown ratings. 

The second antenna though not significantly beneficial really adds more
flexibility to your station. Also part of the fun is justing putting it up
and seeing how it plays. That is what the hobby is all about.

Bill
N6RV

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Sent: Friday, April 09, 2010 12:00 PM
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Subject: SCCC Digest, Vol 88, Issue 7

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Today's Topics:

   1. Re: Stacking Tribander on 54' crank up? (Glenn Rattmann)

----------------------------------------------------------------------

Message: 1
Date: Thu, 08 Apr 2010 12:12:07 -0700
From: Glenn Rattmann <k6na at cts.com>
Subject: Re: [SCCC] Stacking Tribander on 54' crank up?
To: sccc at contesting.com
Message-ID: <20100408191120.AF4C2966E at marlborough.concentric.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

Tim,
I applaud your enthusiasm and energy on this upgrade!

I don't have a lot of specifics to add... your intended antenna hardware
looks good to me.  On the question of whether an extra tribander at 37ft
will help, it may depend somewhat on whether you are in a DX contest, or in
a domestic contest.  The club member who has direct experience with this is
Dave, K6LL over in Yuma.  I believe he has a small tribander down low on his
50ft tower, and a KT-34XA and 40m beam on top.  Perhaps he can comment on
how he used this combo.

I'd guess the diversity gained (two separate directions) and less need for
rotating would be helpful.  But at only 17ft spacing I wouldn't expect any
significant stacking gain (when both are pointed at the same target).  There
may be a bit of stacking gain on 10m, but that may not be fully realized due
to the fact that the antennas are different design and boom length.  So,
being able to point different directions, with quick switching, is probably
the main advantage gained.  To take advantage of the system you will want a
stacking switch (U-L-B) that lets you pick either antenna, or the pair
together (splittiing power in two directions, or one).  Because it has to
work on 3 bands, it will have to be one of the broadband-type switchers,
like Array Solutions stack-match.  No doubt, there will be some interaction
between these two tribanders and your patterns could be affected somewhat.
Modelling might identify some potential serious interactions-- but in
general, I'd guess you could live with it.

You didn't mention SO2R.  K6LL and others have done this with one tower and
tribanders, but it's not trivial.  Of course, you would use passband filters
on the radios.  But, you should probably do some serious calculations to
determine if unwanted signal levels are still too high for the receiver
inputs, even with the presence of the filters.  I recommend the W2VJN book
on this subject, before you start running a kW in SO2R with multiband
antennas only 17ft apart.

At my station I'm fortunate to have a lower 20m beam, and a lower 15m beam
(60 and 90ft), which I can rotate independently from the upper ones.  In
domestic contests I typically park them pointing to Ohio, while the very
high 20/15 pair are aimed at north.  This is helpful in working some of the
rare multipliers up that way, and in picking up some of the weaker W7
callers.  I have diversity switching, U-L-B, to take advantage of any
particular situation.

In DX contests I rotate these antennas as needed, to work the two best
(azimuth) openings at the time.  I very seldom employ stacking gain (both
antennas pointing to the same target) in DX contests, but most often just
split power or go to one antenna.  I might use stacking gain to help work
the VU in a ten-minute opening, but after that is accomplished I usually
swing antennas to separate directions again.  No doubt, the switching is
helpful, and often saves rotation time.  Does it make 10% improvement in
score?  There's really no way to know, but probably not that much.  Just a
guess.

When 10/15m improve, I'd guess the fixed low tribander might be pretty
useful in domestic contests.  If you are able to run with it, and then
rotate your higher one north, it will help you (assumes you have the
switch).  Of course, your 40m beam would then be pointed north a lot of the
time, so you will still have to rotate your main mast to bring the 40m beam
toward the east coast, when you do switch bands.  But hey, this keeps you
awake! ;-)

--Glenn K6NA
PS  The LM-354HD is a really great tower.  Congrats on a good choice!

At 05:43 PM 4/7/2010, you wrote:
>Hi all, I am in the process of budgeting and planning for a LM 354HD 54'
>Crankup tower. It's going in my back yard in place of my current 29' of 
>Rohn 25G. I cannot at this time see having two towers installed as my 
>property is not very big (75X100' lot).
>
>Equipment on the tower will be:
>
>24' 4130 Chromolly mast 2" OD x .250" walls
>M2 Orion Rotator
>TB-2 thrust bearing
>Force 12 C31XR 0.5' above TB-2
>Cushcraft A3WS w/30m 7.5' above TB-2
>Cushcraft XM240 17' above TB-2
>80m shortended Double bazooka on pulley mounted off top section of 
>tower @ 54'
>
>With the above in mind, I was considering placing a second tribander at 37'
>fixed on the north-east (stateside contest running). The tower 
>manufacturer is willing to weld an adapter to allow for this.
>
>My question is... is this worth the expense and extra work? Can I get 
>away with running a TH7DXX (have one on hand) at 37' to run the east 
>coast while running the C31XR at Japan? Am I dreaming here with two 
>different tribanders spread only 17' in height? Will it honestly make a 
>difference in my contest scores (CQP, NAQP, NA Sprint, Sweepstakes)?
>
>Thanks for your thoughts,
>
>Tim, N6WIN.
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End of SCCC Digest, Vol 88, Issue 7
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