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 <[email protected]> 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 <[email protected] > > <mailto:[email protected]>> 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? > > > > _______________________________________________ > > > > > > > > _______________________________________________ > > TowerTalk mailing list > > [email protected] <mailto:[email protected]> > > http://lists.contesting.com/mailman/listinfo/towertalk > > > > _______________________________________________ > > > > _______________________________________________ > TowerTalk mailing list > [email protected] > http://lists.contesting.com/mailman/listinfo/towertalk > _________________ Topband Reflector Archives - http://www.contesting.com/_topband
