>
>
>-----Original Message-----
>From: Don Kessler <ki6sz@compuserve.com>
>To: amps <amps@contesting.com>
To: <amps@contesting.com>
>Date: 07 September 2000 03:40
>Subject: Re: [AMPS] Blown TL922A... What to do?
>
>
>>
>>Tom wrote,
>>
>>"Sounds like you have outgassed. You need to take more nichrome...
>>
>>The tank is typically a virtual short for VHF and UHF energy,
>>because it has a capacitor shunting the input.
>
>That's not quite right, Don. The tune C has inherent inductance, so you get
>resonances. The resonance frequencies vary with shape, size and capacitance
>setting, but in all that I have put on the network analyser, the lowest
>frequency resonance is 'series', or low impedance and the next resonance is
>'parallel' or high impedance. I'm using the term resonance to mean points
>where the impedance goes purely resistive.
>
>The one I looked at yesterday was 100pF max, .06" spacing and about 2.3"
>cube overall. The first, series, resonance came in at 90-150MHz, depending
>on C setting, and the higher one was in the 200-300MHz region. The higher
>frequency one was low Q.
>
>Looking back to previous comments and threads:
>
>The impedance at the capacitor terminal is low either side of the series
>resonant point. How low depends on how far you move in frequency, but it
>doesn't suddenly go high impedance at any frequency 'close' to the resonant
>point.
>
>Adding inductance in series with the capacitor (to simulate the lead from an
>anode) changes the resonant frequencies, but doesn't change the overall
>characteristic.
>
>Adding a L/R parallel circuit in series with the capacitor introduces loss
>as the frequency increases, but does not introduce multiple resonances. As I
>understood what he said, Rich suggested that the separate current paths
>through the L and the R should produce multiple resonances.
I did not say this, Steve.
cheers.
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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