> From: Tom, W8JI:
>
> ...What I've found in real life is the resistor doesn't "steer" the
> null much, it just makes it deeper.
>
> Does it work differently with virtual reality antennas?
>
I can't say that I've done pattern confirmation studies on my
Beverage antennas as I have on my vertical parasitic arrays along
with my past phased vertical arrays (plus having made prior detailed
FCC specified pattern field proofs). I've made assumptions on the
Beverage performance which is a dangerous thing to...
I didn't try to do a worse case search--just looking at the
modeling of a Beverage that I just put up today shows that chosing
a termination resistor for best F/B produces a 58 degree wide area
with a 20 dB minimum null range. My termination resistor chosen
shows a 65 degree wide area with a 20 dB minimum null range and the
four pattern nulls all having greater attenuation at their azimuths
than the similar nulls on the optimum F/B pattern.
There are definite software limitations as well as varying
and generally imprecise ground conductivity parameters that make
exact Beverage performance modeling very difficult. My point is
that I'd rather set my goal at a better pattern even if I'm most
likely failing to precisely achieve it. Highest F/B patterns are
obviously easier to field tune...
Better illustrations would be in horizontal Yagis and phased
vertical arrays. Their modeling is more exact and tuning for the
best front-to-back rarely produces the optimum pattern (unless max.
F/B is your only goal). I still don't understand why the 90 degree
spacing/90 degree phase difference and 180 degree spacing/in-phase
arrays are so common when slightly adjusting the spacing or phase
can produce higher gain with a larger null area...
73, Bill K0HA
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|