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How to calculate power handling capability of a gamma match capacitor
Hi,
I am going to build a variable capacitor for a gamma match in the usual fashion where there is a rod inside a tube by an insulating tube. I need it to handle legal limit, so how would I go about *safely* calculating/estimating the power handling capability of what I have built? Thanks, Scott, WU2X |
#2
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How to calculate power handling capability of a gamma match capacitor
Scott M wrote:
Hi, I am going to build a variable capacitor for a gamma match in the usual fashion where there is a rod inside a tube by an insulating tube. I need it to handle legal limit, so how would I go about *safely* calculating/estimating the power handling capability of what I have built? Thanks, Scott, WU2X Being safe while you do the calculations, or calculating the safe power handling limit? For the former, which you asked, I suggest sitting in a chair with proper ergonomic design..grin But, I suspect what you're really asking is how to go about calculating the power handling limits of the coaxial structure... Consider two factors: 1) High voltage breakdown. What's the breakdown strength of your insulator? If the two tubes are fairly large in diameter, you can probably approximate the field as the voltage divided by the difference in radii. Air breakdown is 30kV/cm in a uniform field. If the ratio of outer to inner diameters is large (so it looks more like coaxial cable), you might want to use a different formula for fields. Don't neglect breakdown along the surface of the insulator. If the "creepage distance" is less than 3 times the free air breakdown distance, then you've got something to worry about. 2) Thermal limits. How much current is being carried by the inner conductor? What's the path to somewhere the heat can be dissipated? For both of these you'll need to model the circuit so you know the current and voltage across your capacitor. |
#3
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How to calculate power handling capability of a gamma match capacitor
"Scott M" wrote in message ... Hi, I am going to build a variable capacitor for a gamma match in the usual fashion where there is a rod inside a tube by an insulating tube. I need it to handle legal limit, so how would I go about *safely* calculating/estimating the power handling capability of what I have built? Thanks, Scott, WU2X do what i do, copy a known design.... the center conductor and insulation from rg-8 (not foam type) works well and takes full power. cushcraft uses 3/16" aluminum rod inside 1/2" aluminum tubing with something that looks a lot like rg-8 poly insulation to make a slip fit. |
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