On Sun, 15 Nov 98 20:11:47 PST "doshhan" <doshhan@vaxxine.com> writes:
>
>Rather than diddle with an extra L (as in PI/L) for another 15 db
>attenuation, I'd consider staying with a simple Pi, and run the amp
>thru an I.C.E. filter that gives an extra 80db attenuation for $34.00
>. The extra bit of attenuation with a Pi/L just doesn't seem to
>justify the additional trouble of the network. I know the other
>advantages of a Pi/L, but still !
>
>Phil VE3OZZ
Thats OK for attenuation above 30MHz but does nothing for harmonics when
operating on the lower bands.
RF pollution is intense around this area particularly during contests.
Many serious contesters are now using switched bandpass filters and/or
stubs to keep the peace.
Yes, L networks increase the cost quite a bit considering the benefit but
they are just one option open to the user.
73 Carl KM1H
>
>----------
To: <amps@contesting.com>
>> Date: Sunday, November 15, 1998 04:23:14
>> From: John Fielding
>> To: km1h@juno.com; amps@contesting.com
>> Subject: Re: [AMPS] Pi-L networks
>>
>>
>> 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!
>>
>> 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. 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.
>>
>> 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
>> >>Submissions: amps@contesting.com
>> >>Administrative requests: amps-REQUEST@contesting.com
>> >>Problems: owner-amps@contesting.com
>> >>Search:
>http://www.contesting.com/km9p/search.htm
>> >>
>> >>
>> >
>> >___________________________________________________________________
>> >You don't need to buy Internet access to use free Internet e-mail.
>> >Get completely free e-mail from Juno at
>http://www.juno.com/getjuno.html
>> >or call Juno at (800) 654-JUNO [654-5866]
>> >
>> >--
>> >FAQ on WWW: http://www.contesting.com/ampfaq.html
>> >Submissions: amps@contesting.com
>> >Administrative requests: amps-REQUEST@contesting.com
>> >Problems: owner-amps@contesting.com
>> >Search: http://www.contesting.com/km9p/search.htm
>> >
>>
>>
>> --
>> FAQ on WWW: http://www.contesting.com/ampfaq.html
>> Submissions: amps@contesting.com
>> Administrative requests: amps-REQUEST@contesting.com
>> Problems: owner-amps@contesting.com
>> Search: http://www.contesting.com/km9p/search.htm
>>
>>
>
>
>
>--
>FAQ on WWW: http://www.contesting.com/ampfaq.html
>Submissions: amps@contesting.com
>Administrative requests: amps-REQUEST@contesting.com
>Problems: owner-amps@contesting.com
>Search: http://www.contesting.com/km9p/search.htm
>
>
___________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com/getjuno.html
or call Juno at (800) 654-JUNO [654-5866]
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|