[TowerTalk] Advise needed on phased beverages

[jimlux]

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 at earthlink.net 
> <mailto:jimlux at 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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