I'm very sorry but I don't undestand what's the relation between Ian's mail
and my previous mail attached at the bottom.
Wasn't my mail clear enough ?
Component Q is one story and used PI network Q totally another one.
The PI Q can be selected but only among the real possible solutions of
the network, not just.
In the HF range if a Q of 10 is applicable, the coil (air or vacuum
capacitors are supposed to have big Q) requirements for such PI are
not so difficult to obtain.
73,
Mauri I4JMY
P.S. Something about the marginal topic of PI resonances....
A PI network can be seen as two back to back L networks matching
a common intermediate impedance between them.
The gap of the L network is that given the loads, only a solution
exists, thus the Q can't be selected but comes out just (Q is
equal to the square root of (Rp/Rs)-1).
L and PI matching networks are low (or high) pass filters and
follow the rules of this kind of 2nd and 3rd order filters.
L network has (one) small resonance (unless the Q is very high) at
the point where the 2 components reactances are the same, in
absolute value.
Stated that's mostly useless to find it out, PI resonances can be
calculated in the same way dividing it into the 2 joined L
networks, as previously described above.
>Rich says:
>
>>? Pi-networks and L networks are not resonant on the working frequency.
>
>What do you mean by 'resonance' in this context? The definition is very
>important.
>
>73
>
>Peter G3RZP
-----Messaggio Originale-----
Da: Rich Measures <measures@vc.net>
A: <itr@nanoteq.co.za>; Maurizio Panicara <i4jmy@iol.it>
Cc: <rakefet@rakefet.com>; Amps reflector <amps@contesting.com>
Data invio: martedì 3 agosto 1999 14.34
Oggetto: Re: R: [AMPS] L-Pi net...downside?
>
>Hams are meant to use grip-dip meters and not worry about "Q" factors.
>On the input circuit (amp "OFF"!), get the deepest dip (check the
>harmonic response), on the output circuit, check for dips across the
>widest frequency range while twiddlying the "load" and "tune" caps. Then
>hope that the tube's input and output impedance doesn't change much as
>soon as its switched on.
? Pi-networks and L networks are not resonant on the working frequency.
>If any dips (other than a nice deep one at the wanted response) are
>noted, Murphy dictates that in the heat of a contest, that combination
>will be tuned by the operator, then possibly bye bye amp.
>
>To tune the thing, if all seems in order:
>Leave the ouptut tuning on best match found, switch on and warm up,
>twiddle the input tuning a bit (exciter's automatic tuner OFF) while
>keeping a beady eye on the location of the HV post, the exciter's full
>power output, the exciter's SWR, and the amp's power output by tweaking
>the "load" and "tune" caps. Compromise for best output power vs input
>SWR. Go and have a cup of coffee while the old nerves unjangle, count
>yourself lucky to have survived such a frightening ordeal.
>Ian, ZS6BTE
>
>Maurizio Panicara wrote:
>>
>> Vic,
>>
>> with some care and a bit of experience in correct positioning and wiring,
>> the problem to find or realize proper components to have and keep a
>> standard PI network whose loaded Q is 10 is a fake one.
>> The problem is that on 10m the residual of plate capacitor plus tube/s
>> internal plate capacitance in some cases are so big that the first usable
Q
>> is not 10 but a much higher value. In that case it's really hard to find
out
>> the proper components (coil) and do not destroy Q with multiband amps
>> related items like wires (even short) and/or switches (even small).
>> If the practical situation allows the design of a PI whose loaded Q is 10
>> and no other parameter is required such network is a totally superflous
>> complication.
>> Go ahead with a symple PI network.
>>
>> 73,
>> Mauri I4JMY
>
>--
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>
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
--
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