the scenario for me typically is that I come back to N4ZA, give him my number
and when he comes back to me I realise he is N4ZR...upon correcting the call
he now is a dupe...big deal....the software says zero points...next QSO.
QRZ
Olde Jim
K4OJ
Known For Orange Juice
The Florida Contest Group
>From broz@csn.net (John Brosnahan) Fri Nov 8 02:29:07 1996
From: broz@csn.net (John Brosnahan) (John Brosnahan)
Subject: RG-8 as Capacitor
Message-ID: <199611080327.AA24805@ns-1.csn.net>
At 08:35 PM 11/7/96 -0600, you wrote:
>Several weeks ago, there was a discussion on the reflector as to feeding a
>inverted-L antenna on 160, Mine works great now, but my variable tuning
>capacitor is a little light for the KW. Someone was talking about making a
>capacitor out of RG-8.
>
>Can some one point me in the right direction to find the information to do
>that? I guess you can use the coax's dielectric between the shield and
>inner conductor. Anyone have any sucess at doing this???
Lee,
Coax works great as a capacitor WHEN THE REQUIRED LENGTH IS VERY
SHORT COMPARED TO A WAVELENGTH. You can use 30 pF per ft and get a
close approximation to the value you need, but you have to remember that
the stuff is a transmission line and the capacitance gets transformed by the
length of the line, resulting in needing more coax than it seems that you
would just based on length. Once you get to 20 or 25 pF at 6M it starts
getting harder and harder "to get there from here". That means that if you need
more than a couple hundred pF on 80M things get a little flakey. You can
overcome this problem by making the required capacitance from a number of
short lengths of cable in parallel--great use for all of those 1-5 ft pieces
left over.
Or you can use a Smith chart and just figure out what you need for the reactance
desired.
Good luck.
John
John Brosnahan W0UN
24115 County Road 40
La Salle, CO 80645
Log Padding is a NON-CONTACT sport! (W0UA)
|