[TowerTalk] Petrezewski (sp?) array ..

[Tom Rauch]

> Just make sure that you isolate the grounds so you
> have no spurious resonances due to common shields
> that will detune the "reflectors" to somewhere that
> limits their usefulness.  Just means that you need
> double-pole relays to switch both the center and shield
> for each dipole.


The reason you have to use DPDT relays is the system has no 
balun at each element, which is a VERY bad move in a directional 
array.

If you install choke baluns (aka current baluns) at some point 
between the element and the common switching system, there is 
no need to switch the shields. 

If the feedlines are 1/4 wl long electrically on the outside of the 
cable, you also would not need a balun or a DPDT relay. A balun 
would do very little good because the common mode impedance 
would already be high on the shields. 

In the case of 1/4 wl or near 1/4 wl long feedlines **without a 
balun** switching the shields will make things worse, and should 
be avoided . In this case the shield and 1/2 of the dipole would be 
RESONANT or near-resonant when the shield was opened!!!
Bad news.






73, Tom W8JI
W8JI@contesting.com 

List Sponsor:  ChampionRadio.com - Trylon self-supporting towers, safety
equipment, rigging gear, LOOS tension guages & more!  http://www.championradio.com

-----
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com