On Feb 22, 2005, at 1:15 PM, TexasRF@aol.com wrote:
>
> In a message dated 2/21/2005 4:47:23 A.M. Central Standard Time,
> r@somis.org writes:
>
>
> On Feb 20, 2005, at 6:35 PM, TexasRF@aol.com wrote:
>
> >
> > Hi Rich, no, I said "C1 resonates the network" but no matter, we both
> > know what the intent was.
>
> No capacitor in a L-network or a Pi-network (double L-network)
> resonates the network.
> Hi Rich, here is the plan for the bullet proof dip meter and test:
The only people who need a test are those who do not yet understand how
an L-network transforms E and I.
> ?
> The PA has an 8877 tube in it with a 1000 ma plate current meter
> installed and connected. We can use this meter to observe the
> resonance "dip". The Pi network is adjusted for maximum output power
> with 75 watts of drive power applied. We have to do this with a dummy
> load so any antenna related influence in our test is eliminated.
> ?
> At resonance, the plate load impedance is all resistive, no shunt
> reactance. Off resonance in the higher frequency direction would
> entail the presence some shunt inductive reactance, which in parallel
> with the plate load resistance would cause the load impedance to be
> lowered. Off resonance in the lower frequency direction would entail
> presence of some shunt capacitive reactance, also lowering the total
> load impedance.
> ?
> Since we know from?Ohm's law that current equals voltage divided by
> resistance (or impedance in an ac circuit) we would expect the plate
> ma meter to?be minimum when the load (network) is at resonance and non
> minimum when the load?(network) is off resonance.?
> ?
> Now comes the dip check: Expecting the network to be non resonant, as
> the driver frequency is slowly changed, in the direction of expected
> resonant frequency, we would expect the plate current to slowly reduce
> until we reach the actual resonant frequency of the load (network). If
> we go the wrong way then the plate current will rise. No problem, we
> just tune the driver frequency in the other direction in this case.
> ?
> Once we find the frequency of minimum plate current (the dip), bingo!
> We have found the resonant frequency of the load (network). If it is
> different than the starting frequency then the idea that Pi networks
> do not operate at resonance will be proven. Also,?no dip meters have
> been sacrificed in the process and any question of what influence is
> caused by cover removal is avoided.
> ?
> Anyone out there willing to give this test procedure a try? I am at
> work right now and no access to a big PA to check this out.
> ?
> Standing by for test results!
It's not a bad idea to make sure that you are in the right gear before
letting out the clutch.
> ?
> Thanks/73,
> Gerald K5GW
>
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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