[TowerTalk] RE : Stubs

[hermans]

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 at contesting.com
[mailto:towertalk-bounces at contesting.com] De la part de Gregg Seidl
Envoyé : mercredi 18 juillet 2007 3:39
À : TowerTalk at 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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