By a rule of thumb, I remember that the "Q" factor of a of a coax cavity (or
line of a quater wave )is maximum when the physical dimensions are close to
a characteristique impedance Z=75 ohms.
Zc=138 divided by Square root of the constant of dielectricum ( Dielec. Cnt
is 1 for dry air.) multiplied by the quotient of lg D/d ( where D equals
outer diam of the screen, d equals diam of the inner conductor.
Sorry for the formule in plain texte.....
I dont remember if I did the math nor do I rember the relation since it was
a rule of thumb. But this was the way we calculated the dimensions of a coax
cavity in VHF/UHF.
The Band pass equals 1/2Q.
Someone can correct me if I am walked beside my boots?
( Use grain sillos as 1/4 wave stub with max Q on HF....HI HI
Jos (did probably the math fourty-five year ago..........!)
-----Message d'origine-----
De : towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] De la part de Gregg Seidl
Envoyé : mercredi 18 juillet 2007 3:39
À : TowerTalk@contesting.com
Objet : [TowerTalk] Stubs
I always thought that the lower-loss cables have a deeper null.I'm not sure
why though.Maybe because the "Q" would be higher??We use lmr-400 clone here
for our stubs and they work well.Just gotta make one that cuts out 40 meters
from 15 yet. Gregg K9KL
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