[BC] Assistance With A PI Network Calculation

[Miltron]

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Well, yes and no, Dana. Your T/Y network is a low pass.   Your pi is high pass, which would not be used in an ATU.
The shunt reactances and the series reactances are the same respectively for pi or T; for a 90 deg they're _all_ the same, except for sign, as Harold said. It's just that the T is easier to adjust as usually built, as no one wants the expense of two variable shunt legs. And in a pi ATU, it's a minor pain to calculate the value of the shunt capacitor on the output leg where you have to compensate for the tower reactance.
M
-----Original Message-----
>From: Dana  Puopolo <dpuopolo at usa.net>
>Sent: Feb 24, 2007 8:07 PM
>To: Broadcasters' Mailing List <broadcast at radiolists.net>
>Subject: Re: [BC] Assistance With A PI Network Calculation
>
>A Y network looks like the letter T with a series coil, shunt cap and another
>series coil.
>
>A pi network looks like the pi symbol (actually more like an unside down U).
>It has a coil to ground, a series cap and a second coil to ground.
>
>-D
>
>------ Original Message ------
>Received: 
>From: "Harold Hallikainen" <harold at hallikainen.com>
>To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
>Subject: Re: [BC] Assistance With A PI Network Calculation
>
>Though I haven't worked it out, I THINK a pi network is similar to a 90
>degree T network. For the T network, each component has the same reactance
>as the "characteristic impedance" of the network. And when using a 90
>degree network to transform impedance, the characteristic impedance of the
>network should be the geometric mean of the source and load impedances
>(square root of the product of the two impedances). See
>http://sujan.hallikainen.org/rw/theory/theory13.html .
>
>Again, just thinking about it, I THINK a pi would behave similarly to an
>L. The math is left as an exercise for the student.
>
>Harold
>
>
>> I was going through my junk box trying to determine what kind
>> of AM transmitter I might be able to build with available
>> parts.  I came up with enough parts for a final power
>> amplifier using three 1625s (12 volt version of the 807) in
>> parallel.  Wonder if someone could give me the approximate
>> values of the input and output capacitors for the PI network
>> at 3.8 MHz?
>>
>> The 1625s will have about 700 volts on the plates with 300 MA
>> which is a plate load of 2333 ohms.  The output of the PI
>> network will of course feed 50 ohms.
>>
>> Thanks,
>>
>> Tom
 

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