>
>snip
>>>I can use a series of measurements to determine the approximate
>>>value of R and L in most cases, but I've also found many cases
>>>that require testing of several PA's to optimize suppression. A
>>>simple formula would certainly save work!
>>>
>>/\ First off, one needs to realize that roughly equal currents need to
>>flow in L=supp and R-supp at the anode's VHF resonant freq.
>Why is this ratio optimum? I would have expected to get greater damping if
>you put a higher percentage of the current through the resistor.
/\ The L/R VHF parasitic osc. suppressor has two current paths. Since
the magnetic fields from these two currents are at right angles to each
other and the inductances are not equal, a staggered-resonance effect is
produced. This tends to decrease the Q of the (virtually unavoidable)
VHF resonance in the anode circuit. Because the peak E amplitude of the
damped-wave ringing is proportional to the Q of the resonant circuit
multiplied by delta-I, lower Q (and Rp) tends to increase stability. By
dividing the VHF ringing current equally, neither resonance dominates the
picture.
cheers, Steve
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
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