On 11/24/20 9:28 AM, RVZ via TowerTalk wrote:
Hi Dennis, That's a great idea but I'd need to make a high power LC circuit and don't have the parts. Also, it would need to handle 1,500 watts for heavy-duty contest use so it would require hefty parts. Every time I've tried a Shunt Feed system in the past the SWR gradually changes as the contest goes on. Do you have a recommendation as to where I could acquire parts for an LC circuit that would stay rock stable after several hours of use?
Well - the inductor is going to be some sort of air core - and it will
be reasonably stable over temperature.
It's the capacitor that's going to give you grief, if it's not a air and
plate (or vacuum variable).
Doorknobs are notorious for changing with temperature and for gradual
change in C due to degradation from HV, as are many ceramic capacitors,
unless they're designed for this kind of duty. ATC makes some
multilayer high current capacitors that are pretty robust, as do
Johansen and AVX.
How much capacitance do you need? I looked at some examples and they're
looking for around 500-1000 pF.
ATC 100C at 510 pF and 700Vrms , part # 100C 511 J W 1000 X
https://atceramics.com/userFiles/uploads/pdfs/100c.pdf
Or Kemet, or AVX
Kemet C322C511JDG5TA 0.1% dissipation factor at 1 MHz (Q=1000) - zero
temp coefficient.
https://www.mouser.com/datasheet/2/212/KEM_C1054_HIVOLT_GOLDMAX_300_C0G-1140500.pdf
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