On Aug 25, 2005, at 9:33 PM, KD7QAE wrote:
> So, many of the plate chokes I have seen described in home brew
> amplifiers and those in use in Ameritron, Henry, Alpha and QRO are
> single layer wound solenoids, many like the one I built. These do not
> exhibit resonant peaks (High Z) in the ham bands as far as I can tell
> based on my limited experience.
A single-layer choke of up to c. 60uH will exhibit no resonances below
approximately 35MHz, however, larger chokes will.
> I am very confused by the assertions
> that I need to build something materially different than these examples
> or face a very inefficient and perhaps flaming amplifier.
Choke fires are definitely not an old wives' tale. To avoid burning
one's hair, choke resonances need to be parked with care
>
> Michael Tope wrote:
>
>> ----- Original Message -----
>> From: "Jim Forsyth" <jim@forsyth.net>
>>
>>
>>
>>> This mini thread is about a case where the resistance of the
>>> inductor WAS
>>> significant and possibly DID affect the resonant frequency
>>> appreciably.
>>>
>>> Jim, AF6O
>>>
>>>
>>>
>>>> At the risk of sticking my foot in my mouth again, R generally
>>>> doesn't effect the resonant frequency of an RLC circuit appreciably
>>>> provided that the Q is reasonably high. On the other hand, a plate
>>>> choke when you look at it very closely is really a distributed RLC
>>>> circuit, so one has to be careful about applying simplified 3
>>>> component
>>>> lumped element models. I'd love to see a rigorous analytical
>>>> treatment
>>>> of this if anyone knows of a good reference.
>>>>
>>>> 73 de Mike, W4EF........................................
>>>>
>>>>
>>
>> Yes, I understand that, Jim, but I was having a hard time believing
>> that
>> you could get away with deQing a choke enough to shift the resonant
>> frequency significantly without turning it into a fireworks display.
>> I did
>> some google searching and there seems to be little in the way of
>> analytical information on plate choke design. Mostly it seems to be
>> an empirical art (e.g. use X # of turns closewound on a D diameter
>> form kind of thing). My best guess of the equivalent circuit would be
>> a bunch parallel RLCs in series, but even that I suspect is
>> oversimplified.
>> The fact that it has multiple staggered parallel and series
>> resonances,
>> for instance, can't be explained by a simple 3 component lumped RLC
>> model.
>>
>> 73 de Mike, W4EF..............................................
>>
>>
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>>
>>
>
>
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>
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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