[Amps] wires through center of coax

[Fuqua, Bill L]

I believe in your case the RF potential between the wire and the inside of the inner conductor are the same at the entrance.
This is fine. Earlier I said that would be a condition that would work. We   1/4 wave chokes in in our Mobley buncher amplifier years ago.
They were a bit long since it operated at 20MHz our newer post acceleration Klystron buncher operates at 90 MHz is a bit more conventional in design.
Basically a 12kW FM transmitter syncronized to our beam pulse.  Must be fun to work with MegaWatts of RF.   I can see that it may
get exciting at times. We work at much lower energy.

73
Bill wa4lav
 
   
________________________________________
From: John Lyles [jtml at losalamos.com]
Sent: Tuesday, December 21, 2010 1:13 AM
To: Fuqua, Bill L
Subject: Re: [Amps] wires through center of coax

Bill
In my example, the wire enters the central region of the center
conductor, which is over 3 inches OD. It comes in through a short
circuit via a quarter wave stub at the operating freq., so the wire is
grounded at that end. Actually it is a pair of wires which go to a 100
ohm platinum RTD, to measure temperature of a capacitor paddle at the
other end of the coax line. So I don't care what the coaxial capacitor
is in there, as long as main RF currents on the OD of the center
conductor and ID of the outer conductors do not penetrate into the
central region where the wire is.

Best Regards
John

On 12/20/10 2:56 PM, Fuqua, Bill L wrote:
> It can be done under the right conditions. for example if the wire is at the same RF potential
> as the RF as it enters the coax. Then it just becomes part of the center conductor.  But if it
> is not then, as an example ,the wire is at ground potential then you have produced a coaxial capacitor
> that will create some other impedance than the coax's characteristic impedance.
>      Sometimes you will see wires going down thru coaxal resonators but on the ends they are held to the
> same potentials as the ends of the center conductor.
>
> 73
> Bill wa4lav
> ________________________________________
> From: amps-bounces at contesting.com [amps-bounces at contesting.com] On Behalf Of John Lyles [jtml at losalamos.com]
> Sent: Monday, December 20, 2010 2:12 AM
> To: amps at contesting.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
>
>
>>       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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