On Sun, 15 Nov 1998 14:23:14 +0200 "John Fielding"
<johnf@futurenet.co.za> writes:
>
>Hi Carl - I am currently designing my "ultimate amplifier" using a
>Pi-L
>network. Like you I struggled to calculate the necessary values, that
>is
>until I used the ARRL Radio Designer software!
Havent tried that software yet John; used to do it by hand but now using
DOS based engr programs that my son got at college.
>
>I designed the Pi section to match into 300 ohms first of all, and
>then
>having optimised the values (comparing them to the values published in
>the
>ARRL Handbook). I then "fixed" these in the program and optimised
>the L on
>the output.
Optimise how? What Q did you wind up with in the L?
Works pretty good, the predicted response is always
>better
>than 30dB down at twice the working frequency. Input match (as the
>anode
>sees it) is better than -30dB and S22 is about the same.
Have you tried it at power yet? Getting it to work on paper was no
problem for me....it just was unruly at QRO until I reduced the L Q.
B&W had similar results when they first bought the Viewstar PT-2500A.
73 Carl KM1H
>
>Thought this may be of interest to all on the net.
>
>John ZS5JF
>
>
>-----Original Message-----
>From: km1h@juno.com <km1h@juno.com>
>To: amps@contesting.com <amps@contesting.com>
To: <amps@contesting.com>
>Date: Saturday, November 14, 1998 6:29 AM
>Subject: Re: [AMPS] Pi-L networks
>
>
>>
>>
>>
>>On Fri, 13 Nov 1998 12:47:23 -0000 Peter Chadwick
>><Peter_Chadwick@mitel.com> writes:
>>>
>>>Does anyone have any comments about the Q of the L network section
>in
>>>Pi-L
>>>networks? I have seen it suggested that the impedance at the middle
>of
>>>the
>>>pi-L should be the geometric mean of the input and output
>impedances:
>>>the Q
>>>of the L will then be given by
>>>
>>>Q = sq.rt.(Ri - Rl)/Rl
>>>
>>>where Ri is the intermediate impedance in the Pi-L (i.e. the
>geometric
>>>mean)
>>>and Rl is the load impedance (usually 50 ohms)
>>>
>>>For an 1800ohm plate load, this gives a Q of 5 for the L section,
>>>which
>>>appears to be the right order of magnitude.
>>>
>>>Of course, the Pi section would run at the usual Q - 10 to 15, or
>so.
>>>
>>>Comments, please?
>>>
>>>73
>>>
>>>Peter G3RZP
>>
>>Peter,
>>I thought the same until I started to actually use that concept
>>Peter....wound up with higher than expected voltage at the Load
>>capacitor....read "arcs".
>>By formula that should not have occured leading me to believe that
>there
>>is more to it than static design on a piece of paper.
>>I now "design" for a Q of 2 to 3 in the L and have had no further
>bad
>>experiences. The spectrum analyzer confirms the L is performing as
>>expected.
>>
>>73 Carl KM1H
>>
>>
>>
>>>
>>>--
>>>FAQ on WWW: http://www.contesting.com/ampfaq.html
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>>>
>>>
>>
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>
>
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>
>
___________________________________________________________________
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Get completely free e-mail from Juno at http://www.juno.com/getjuno.html
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Administrative requests: amps-REQUEST@contesting.com
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