Actually when I meant to maximize the forward gain then that implied only
giving up maybe 5db front to back. Say, from 25 to 20. And usually with
those OWA stacks I modelled the F/B got maybe worse only on low angles, thus
I wouldn't mind some DX coming in to the back of my beam.
Definitely they are both important but I wouldn't want to give up 0.5 db
gain for better F/B. I think 1 db of gain would mean about 1-2% difference
in the CQWW score on average.
Moving those long boom antennas closer actually maximizes vertical angle
coverage. If you read my long post a few days ago then I describe in my
example that when stacking 2 beams only 0.5 wl you get another usable lobe
while when the spacing is larger you are heating up the air at 90 degrees.
And should you have a stack of four, as Jiri has on 10m (13;19;25;31), you
are able to switch them so that you get every possible angle out exept very
low of course. That exactly what I would use on 10m if I couldn't go higher.
73s
Tonno
ES5TV
----- Original Message -----
From: "Bill Tippett" <btippett@alum.mit.edu>
To: <towertalk@contesting.com>; <tonno.vahk@mail.ee>; <jirka@jimaz.cz>
Sent: Sunday, July 29, 2001 3:48 PM
Subject: Re: [TowerTalk] The best stacking distance for long-boom yagis -
0.5 wavelength!!
>
> Hello Tonno, Jiri et al!
>
> I was curious about your statements:
>
> Tonno ES5TV wrote:
>
> >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.
>
> What are you trying to maximize for contesting? Several years ago
> I was of the opinion that poor F/B was actually desirable for contests,
> especially when I was using only one antenna. Having used my stack for a
> couple of years, I now believe F/B is more important. My reasoning is
that
> I believe a good pattern (F/B) is extremely important for hearing the very
> weak stations better in heavy QRM. If I want to hear in another
direction,
> for example EU and SA, I am more likely to spray my transmit signal to
> cover both areas on transmit, but then listen only in the desired
direction
> for very weak signals by switching on receive. The same may apply to
> takeoff angles...I want to maximize my vertical angles on transmit, but
> then I want to select the best combination to hear very weak signals. I
> think you are saying maximize for angle coverage but why not better F/B
> also?
>
> Jiri OK1RI wrote:
>
> >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.
>
> I also don't understand how moving antennas closer maximizes
> vertical angle coverage...I think this would make the vertical angle
smaller
> (centered for the height of the stack midpoint). I prefer a stack with
fairly
> wide vertical separation. If signals are extremely low angle, the full
> 3-stack or top 2-stack combination will be best. If signals are fairly
> high angle, the lower 2-stack will be best. If signals are very high
> angle, the lower antenna alone will be best. Maybe you are talking about
> always using your stacks as full combinations and not switching them as I
> do using the StackMatch (any combination of the 3 antennas). Is that what
> you mean?
>
> In my opinion the most important parameters to maximize are as
> follows (approximately in order but #1 and #2 are very close):
>
> 1. Azimuth angle coverage (not just beamwidth of a single Yagi but also
the
> ability to spray in multiple directions simultaneously)...this can of
course
> be accomplished by being able to independently rotate antennas in a single
> stack or better yet have another separate set of antennnas that can easily
> switched/combined for other directions.
>
> 2. Vertical angle coverage (transmit with a broad vertical angle but
switch
> on receive to optimize S/N for weak signals).
>
> 3. F/B or pattern of the array is very important when trying to optimize
> S/N when receiving weak signals.
>
> 4. Forward gain is least important! When 10M is wide open, a dB or two
> is insignificant (S9 + 40 dB versus S9 + 41 dB). This is also why guys
> who run illegal power are really wasting their efforts in the wrong area
> IMHO!
>
> I would be curious to know your thoughts on the above.
>
> 73, Bill W4ZV
>
>
>
>
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