The usual method is to lift the first chokes ground lead with a vacuum relay
and another (or a dpdt one) to remove the short around the 2nd choke. A
variant is to leave the second choke in the circuit.
Carl
KM1H
----- Original Message -----
From: "Vic K2VCO" <vic@rakefet.com>
To: <amps@contesting.com>
Sent: Friday, June 10, 2011 1:22 PM
Subject: Re: [Amps] RF choke switching
Correct, but if there is a bypass capacitor to ground in between the chokes,
then the
additional impedance provided by the big choke -- even if lower than it
could be due to a
nearby resonance -- is still useful. The voltage applied to it will be much
lower than if
it were the only choke in the circuit and it won't burn out. So at worst the
second choke
would not be of much help on certain frequencies.
On 6/10/2011 8:09 AM, Larry Benko wrote:
> Vic,
>
> Look at my post of a few hours ago. Two non-resonant chokes in series
> can together be resonant. This is basic circuit theory and there is no
> way around the issue.
>
> Larry, W0QE
>
> On 6/10/2011 8:43 AM, Vic K2VCO wrote:
>> Because if I do this, the bigger choke will be out of the circuit
>> completely on the high
>> bands. My method will leave it there, after the bypass, to provide
>> additional filtering on
>> the HV lead to the power supply.
>>
>> On 6/9/2011 11:12 PM, Angel Vilaseca wrote:
>>> Vic,
>>>
>>> Why not use the vacuum relay to short the big choke? That is what is
>>> done on the tank
>>> circuit when bandswitchig.
>>>
>>> 73 de HB9SLV
>>>
>>> Vic K2VCO a écrit :
>>>> I'm planning another amplifier (2 x 4-400A, 1.8-28 mHz) and I was
>>>> thinking that I would
>>>> deal with the "RF choke problem" by having two chokes in series. The
>>>> one nearest the
>>>> plates will have enough inductance for 20-15-10 meters with no series
>>>> resonances below
>>>> 30 mHz. The second will be 1 or 2 mh to provide enough inductance for
>>>> the 1.8-7 mHz
>>>> bands. I will use a vacuum relay to connect a bypass capacitor from the
>>>> junction of the
>>>> two chokes to ground on the high bands. Of course there will be further
>>>> bypassing at the
>>>> cold end of the big choke.
>>>>
>>>> That way, both chokes will always be in the circuit to help keep RF out
>>>> of the power
>>>> supply but the resonances and distributed capacity of the large one
>>>> won't upset the
>>>> higher bands.
>>>>
>>>> Is this a good idea or am I missing something?
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--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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