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Re: [Amps] plate bypass capacitor

To: <amps@contesting.com>
Subject: Re: [Amps] plate bypass capacitor
From: "Roy" <royanjoy@ncn.net>
Date: Sat, 8 Aug 2009 12:46:15 -0500
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Concerning,

"...At 80 meters, 100uH has a
 reactance of 2.2 kiloohms. At 1000V RF, that would make 0.45A of RF
 current going through the choke, and this is the current that the bypass
 cap has to conduct to ground, unless there is something else 
helping...(etc.)"


Plate solenoid choke rated values of inductances are measured at a low audio 
frequency. At RF frequencies they exhibit much, much higher effective 
impedances of up to over a megohm at their first fundamental parallel self 
resonance, which is ideally put into use for highest efficiency.  At 
frequencies lower than the first parallel self resonance, they still reflect 
typically ballpark Zs of about 30,000 ohms or much more to the plate tank 
circuit. This is due to the principle of many self-parallel resonances 
within the windings. So on 80 meters at 1000 volts RF, current through the 
bypass cap would be on the order of only 30 mA or 0.03 A for a 100 uH choke, 
maximum...even smaller currents are likely in practice due to surrounding 
grounded surfaces lowering the primary resonant point. Stay away from 
fundamental series resonances. References are from Ohmite plate RF choke 
engineering papers.

73,  Roy           K6XK 


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