Hi Tonno,
Broadside phased Beverages and short verticals do work! As you
should have seen in your modelling, broadside spacing determines
the angle of radiation with optimum front-to-side ratio.
I've had excellent results with broadside phased Beverages at W3LPL,
and more recently with broadside-endfire arrays of short verticals
(W8JI passive 8-circle arrays).
Beverages and short verticals are so lossy that they don't interact with
each other even at very small spacings.
During my professional career I worked on Beverage arrays with 32,
64 and 128 broadside phased Beverages for 3 to 30 MHz. The Beverages
were installed over a field as precisely flat as a football field but much
larger. There were no obstructions or other antennas within hundreds
of meters of the array. in every direction.
The patterns were verified by a transmitter flown on an aircraft -- flying
in a precisely controlled pattern accurately reported by telemetry --
and received by the Beverage array. I wish we could afford to do
this precision pattern measurement with our ham antennas!
On 160 meters you should achieve best results by phasing just the
two outer Beverages. The middle Beverage doesn't contribute much,
as you should see in your model.
On 80 meters your Beverages are probably too long, its likely that
signals arriving at the far end of your Beverage have the wrong phase
relationship to signals arriving at the near end. Y ou should achieve
the best results by phasing only the two closest Beverages.
Your model won't accurately predict this because antenna models
always -- incorrectly -- assume a constant-phase received signal
wave front. In many cases the wave front on 80 meters will not be
phase coherent across an array more than one wavelength wide
nd/or more than one wavelength long.
Perhaps your lack of broadside directivity is caused by common
mode signals leaking into your system from the outside of the coax
cable shields. You didn't mention common mode chokes in your
antenna description,
73
Frank
W3LPL
----- Original Message -----
From: "Herbert Schoenbohm" <herbert.schoenbohm@gmail.com>
To: jimlux@earthlink.net, "TopBand List" <topband@contesting.com>
Sent: Tuesday, September 11, 2018 3:27:12 PM
Subject: Re: Topband: [TowerTalk] Advise needed on phased beverages
Jim, yes, I suspected they might interact of course. But can I avoid it?
> ungrounding both ends of the unused beverage would also not eliminate
> coupling I am afraid?
If the feedlines are a half wave or multiples of a half wave you should try
terminating the unused shack end. This electrically places the termination
right at the feed point.
Herb Schoenbohm, KV4FZ
On Tue, Sep 11, 2018 at 11:10 AM jimlux <jimlux@earthlink.net> wrote:
> On 9/11/18 6:19 AM, Tonno Vahk wrote:
> > Jim, yes, I suspected they might interact of course. But can I avoid it?
> > ungrounding both ends of the unused beverage would also not eliminate
> > coupling I am afraid?
>
> Exactly... no convenient way to change it in the field.
>
> A model can tell - run the model with the wire in and wire not in and
> see what the difference is.
>
>
> >
> > Height is ca 2m +/- 0.5m.
> >
> > I did not model switching in any other way than simply creating
> > feedpoint for both beverages. No feedlines in the model. Could such long
> > feedlines even if the same length, create a trouble?
>
> Sure - the feedline is an impedance transformer, so it changes the
> impedance at the feed end of the antenna. For instance, if it were a
> quarter wavelength (or an odd multiple), if you short the shack end,
> it's an open at the antenna end, and vice versa.
>
> I'm not sure how sensitive a beverage is to end termination impedance.
>
> If you're using NEC or a derivative, you can put a TL card or NT card in
> to do the transmission line and the model will show the effect.
>
>
> >
> > On 11 Sep 2018, at 15:19, jimlux <jimlux@earthlink.net
> > <mailto:jimlux@earthlink.net>> wrote:
> >
> > On 9/11/18 5:00 AM, Tonno Vahk wrote:
> >> Hi,
> >> Last weekend I finally got into experimenting with phased beverages,
> >> something I was planning for some time.
> >> I installed 3 broadside 219m (718ft) long beverages into the forest
> >> looking at 90 degrees and separated 60m (200ft) from each other (120m
> >> between the outer ones).
> >> I took great care to make sure the wires are straight and fully
> >> parallel to each other as well as starting from the the same line.
> >> I use DXE 9:1 beverage transformers and DXE 470 ohm termination
> resistors.
> >> I brought 150m (500ft) 50 ohm cable from each beverage feedpoint to
> >> the shack and connected to Microham Stack Switch (like Stackmatch).
> >> All the cables were of identical length to ensure same phasing.
> >> So I presume this system gives me full ability to test any combination
> >> of those 3 beverages alone or phased with each other?
> >> Well, all the 3 beverages alone are quite identical indeed which is
> good.
> >> But now when switched in pairs or all 3 together I am not seeing much
> >> effect. I do know what the patterns should look like and I presumed
> >> the effect would be strong especially with signals coming from side
> >> but most of the time I notice no difference with any signals when
> >> comparing any single beverages to combinations.
> >> This is puzzling. Modelling suggests I should for example have very
> >> big improvements in suppressing signals 45 degrees off on 160m when
> >> using 2 phased beverages 120m apart as well as when using all 3
> >> beverages on 80m but I did not notice such drops of 10-20db almost in
> >> any signals from any off directions.
> >> I could hardly notice sometimes the expected 3-5db increase in the
> >> signals from the right direction but not always as well.
> >> Can some of you having experiences with phased beverages tell me if I
> >> have done something wrong in my setup?? Should I test them
> >> differently? Are the phased beverages overrated and in real life there
> >> is seldom a significant improvement over 1 single wire beverage that
> >> is already long enough like 220m in my case?
> >> Look forward to any input. I can send the modelled patterns and maps
> >> of my beverages in picture files to anyone interested.
> >
> >
> >
> > 60m (your separation) is about 3/8 wavelength on 160, and the elements
> > are long (1 1/8th wavelength) so they'll interact signficantly, even if
> > disconnected from the feed (just like parasitic elements on a Yagi).
> >
> > How high off the ground are the wires?
> >
> > How did you model the switching?
> >
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> >
> >
> >
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