>
>K5PC wrote:
>
>"Make sure you have an RF choke accross the output of the amp because is is
>just a matter of time until those "TV" type doorknobs are going to smoke.
>They are not RF rated for 1500 watts."
>
>Not to argue with K5PC, but I've had such caps as plate blockers in my 15M
>3-1000Z for ten years with no problems whatsoever.
>
>What is it about these caps that makes them unsuitable? Ceramic design,
>15KV rating, and with appropriate amounts of C - what is it?
>
? There are no current ratings. Some can handle RF current. Some not.
. Thus, the only way to find out how much current they can safely
handle is to conduct a heating test. I do the test on 1.8MHz (the worst
case) using a paralled roller coil to resonate the 500pF, which is
connected in parallel with a 50-ohm termination. I apply power and check
for heating/ increasing SWR. I measure the potential across the
paralleled circuit, and calculate amperes. TV doorknobs have the wrong
temp. coefficient for use in tuned circuits. // Another problem is that
using two or more caps. for DC blocker service creates an additional
VHF-resonance.
- later, Dave.
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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