Sat, 28 Jul 2001 11:36:52 +0300
Thanks, Jiri, for showing up as I hoped.
I had this 6/6/6/6 @13/19/25/31m of yours exactly in mind when I pointed out
that I might not be the only one stacking them so close.
Have you found any difference in stacking OWA and ordinary yagis? As it
seems to me that 0.5-0.6wl goes even better with OWA.
Maybe I should have emphasized in my post that I wanted to find the best
stacking distance for contesting! Not to maximize F/B definitely.
And I was using flat terrain when modelling. The height and the quality of
ground did not have much to do with the results.
But the fact that you get this fat high 90 degree lobe when moving wider
from 0.5-0.6 wl remains.
As my post was so long that many people did not make it till the end
probably I would post my 3 questions again:)
1.How bad is the exsistence of the high fat lobe at 90 degrees? Does it
effect also near field - other antennas on the tower??? Does it cause
interference?
2. Can I trust AO on that? I have found that there is almost perfect match
between AO results and field measurement as far as I can go (impedances,
SWR, etc.)
so I would trust it.
3. Are there any disadvantages when closely stacking beams that I have
failed to notice?
After all it seems that some people have paid too little attention on
modelling their stacks before putting them up and rather relying on "rules
of thumb" and others' opinions and I suspect that contesting community in
total is wasting quite a few db-s this way heating up the air.:)
73s
Tonno
ES5TV
----- Original Message -----
From: "Jiri Sanda" <jirka@jimaz.cz>
To: "towertalk" <towertalk@contesting.com>
Sent: Friday, July 27, 2001 11:00 PM
Subject: RE: [TowerTalk] The best stacking distance for long-boom yagis -
0.5 wavelength!!
>
> Hello all,
>
> since I was directly asked I will come with some answer - or my perception
> of the problem.
>
> 1.It is important to answer the question why to stack the antennas. There
is
> a bunch of answers:
>
> On VHF to obtain more gain for "direct" propagation - not our case, here
you
> want to stack the antennas for maximum forward gain - i.e. the rules
> pronounced by Bill are more-less correct - a little over 1 WL for 1WL
boom.
> etc. There is quite interesting study on this topic on SM5BSZ page and of
> course the "BIBLE" of antenna modeling - www.cebik.com
>
> 2.ON HF I am sure that this is only one - less important point, what you
> really want to do is to cover as many vertical angles as possible. To
> achieve this you need to have the antennas closer.
> Again there is not an easy answer. I do not believe modeling will give you
> real answers since:
> a. I do not know - may be someone much smarter then myself knows - in
which
> angles in a given period of time you want to radiate !?!?!?
> Observation from this year IARU - I was running OL1HQ on 20m SSB. Around
my
> sunrise there was a peculiar propagation - As I have said here several
> times - we do have 2 more-less similar antennas - 6Y (16m boom) + 5Y
(14.5m
> boom) the first one in 24m, the other on other tower in 52m. The
propagation
> was so that it looked like as a completely different frequencies. The
W6/7+
> KH6 comming 59 ! on the high antenna were absolutely not audible on the
low
> one and the W2,3,4 comming over 59 on the low one were absolutely not
> audible on the high one - by absolutely I mean completely NOTHING ! And to
> make the thing more complicated you might hear W3 on the high one better
> than on the low one and W7 better on the low one ?!?!?!? (by the prefixes
i
> mean real location confirmed by zone - not the silly vanity calls I
> personaly do not like - W5 should be in TX, OK... not in NH or CA !)
>
> b.The influence of real ground on the vertical angles of radiation is
> crucial - try to play with different ground models...., terrain slope.....
> Can you pronounce all those variables coming into question. I can not and
> the difference is HUGE !
>
> 3.The amount of energy radiated over the whole space is of course in all
> cases the same. I.e. if you radiate the energy somewhere where you do not
> want it - it will be "missing" somewhere else.
>
> What we (me + OK1RF) have done was putting the antennas closer. We have
had
> for ages 6/6/6 on 10m. They were @12/20/28m since 1986. Last spring we
have
> made an upgrade to this tower and it is now 6/6/6/6 @13/19/25/31m and it
is
> considerable difference. I can not make direct comparison it is just
> "feeling" By modeling we get there just a few 1/10 of dB more - so nothing
> but the vertical diagram looks to me much better. OK2RZ have done a lot of
> testing on 10m and the results are not easily interpretable. What is good
> varies with type of propagation, time of day........
>
> One more thing - do not trust to AO too much. It uses the MININEC 3.02
> engine. It will give you just rough answers. The NEC-2 engines will give
you
> better answers concerning radiation patterns but less precise answers
> concerning impedances and element length. It is a question for NEC-4 or
it's
> competitor EM-professional to get more reasonable answers.
>
> Have I helped ?
>
> 73 !
>
> Jiri
> OK1RI
>
>
>
>
>
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