Date: Mon, 20 Dec 2010 00:12:23 -0700
From: John Lyles <jtml@losalamos.com>
Subject: [Amps] wires through center of coax
Bill - WA4LAV
I hope that running wires through coax center conductor like this won't
cause problems because I am doing it with the 9 3/16 inch diameter
output feeder of a new amplifier I have been working on. I have a
mechanical linkage going through the middler of the center conductor to
the tuning paddle in the cavity amplifier. Also, have a RTD applied to
the back of the paddle (inside) to measure temperature when it is
running. The linkage and wires run through a 1/4 wave stub into the 3
megawatt PA.
73
John
K5PRO
### Running compressed, dry air, < 5% RH [ typ 2-3 psi] up through the
center conductor has been done for a long time..and ditto with the cavity
between the outer and inner conductor's. U have to..or u will get condensation
inside em...
esp when used outdoors.. for broadcast use up tall tower's. Running wires
inside the center conductor should not be a problem... Until the wire exits
out either end... or through the sides via a special fitting.
Jim VE7RF
> I give up. I think most everyone else gets it. It is like a conversation
> I had with some old hams, not much older than I am aboiut some large coax.
> They were convinced that since the center conductor was hollow you could run
> wires up thru it to carry current to lights and rotators without affecting the
> impedance of the coax. Their argument was that current only flows on the
> outside of the conductors. But that is not always true.
> Current flows on the surfaces and in the case of a hollow conductor it is
> true it will flow on the outside as long there is nothing to electric
> create fields on the inside. There are electric/magnetic fields between the
> outside of the inner conductor and the inside of the outer conductor. But
> once you put a conductor on the inside of the hollow inner conductor you have
> created a new bit of transmission line, there are fields now between the new
> conductors and the inside on the inner conductor. That changes everything.
>
> 73
> Bill wa4lav
>
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