All,

What methods are commonly used to dissipate high RF power in vacuum
chambers, apart from conduction cooled plates?

Any response is welcomed.

Thanks.

Bobby.

Bobby wrote:
All,

What methods are commonly used to dissipate high RF power in vacuum
chambers, apart from conduction cooled plates?

DO you mean cooling the transmitter circuits, or absorbing the
transmitted RF from the satellite or whatever?

Heat pipes are used to pull heat from circuits to an external radiative
heat sink on satellites.

NASA and such places probably have aneonic(sp!) graphite cone RF
absorbing foam on the walls of the chamber.

Bobby wrote:

All,

What methods are commonly used to dissipate high RF power in vacuum
chambers, apart from conduction cooled plates?

Any response is welcomed.

Thanks.

Bobby.

Well apart from forced air or water cooling for anodes, the heat from
cathodes isn't enough to
have to worry about since its heat radiates to the anode where it is
removed by anode cooling.
The tungsten cathodes of large RF tubes need to run hot so they don't
try to cool them.


Patrick Turner.

Patrick Turner wrote:
Bobby wrote:

All,

What methods are commonly used to dissipate high RF power in vacuum
chambers, apart from conduction cooled plates?

Any response is welcomed.

Thanks.

Bobby.

Well apart from forced air or water cooling for anodes, the heat from
cathodes isn't enough to
have to worry about since its heat radiates to the anode where it is
removed by anode cooling.

Try running a 3CX1500A7/8877 heater with no forced air through the
base. Expected lifetime 30 minutes.

The tungsten cathodes of large RF tubes need to run hot so they don't
try to cool them.

All thermionic valve cathodes have to run hot, the clue is in the THERM
bit of THERMionic. No heat, no free electrons.

The cathode itself _must_ run hot. However the metal/glass or
metal/ceramic seals have a very much lower tolerance of high
temperatures. Cooling of the cathode seals is essential for most high
power tubes.

Many of the older 'carbon' anode glass RF power tubes (e.g. 3/500Z)
need to run the anodes at dull red heat (~1000C) to activate the
thorium getter which is coated onto the outside of the anode. This is a
very good reason _not_ to run typical linear amplifiers at less than
their rated output - you will kill the cathodes by positive ion
bombardment.

To answer the original question, the only way to dissipate RF power in
a vacuum is to radiate it from an aerial. All the previous answers have
been about dissipating the heat produced as a by-product of RF power
generation. In a vacuum chamber, getting good coupling into the walls
may be difficult so the aerial may nor work as expected. Tuned
recieving aerials with resistive loads may be needed.

best

Andy