On 12/20/2010 5:21 PM, Fuqua, Bill L wrote:
> It just occurred:
>
> The characteristic impedance of a transmission line is equal the square
> root of the unit length inductance divided by the unit length capacitance.
> By adding a conductor on the inside of the hollow center conductor that is
> not at the same potential as the holllow center conductor you change the unit
> length capacitance.
The unit length capacitance is *between* the inner and outer
conductors. Lines fed in through stubs will have no effect on this unit
length capacitance .
73
Roger (K8RI)
> If the wire is at the same potential as the shield the character
> impedance will be lowered. That does not necessary make it a bad transmission
> line but
> one of a different impedance.
>
> 73
> Bill wa4lav
>
> ________________________________________
> From: Fuqua, Bill L
> Sent: Monday, December 20, 2010 5:07 PM
> To: Fuqua, Bill L; Jim Thomson; amps@contesting.com
> Subject: RE: [Amps] wires through center of coax
>
> If the potentials on the wire as it enters and exits the hollow center
> conductor maintained the same as that on the center conductor and it may
> also be necessary to have the same velocity factor for the wire going thru
> the center conductor as well.
> Use of chokes on both ends of the wires and having the came dielectric
> constant between the wire and inside of the center conductor as you have
> between the center conductor and outer one.
> 73
> bill wa4lav
>
> ________________________________________
> From: amps-bounces@contesting.com [amps-bounces@contesting.com] On Behalf Of
> Fuqua, Bill L [wlfuqu00@uky.edu]
> Sent: Monday, December 20, 2010 4:53 PM
> To: Jim Thomson; amps@contesting.com
> Subject: Re: [Amps] wires through center of coax
>
> Under the right conditions it can be done.
> ________________________________________
> From: amps-bounces@contesting.com [amps-bounces@contesting.com] On Behalf Of
> Jim Thomson [jim.thom@telus.net]
> Sent: Monday, December 20, 2010 11:04 AM
> To: amps@contesting.com
> Subject: [Amps] wires through center of coax
>
> 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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