Carl wrote:
> Or find someone with Microwave Office and plug in the numbers at let it do
> the math. Ive used that program for everything from VHF to millimeter wave
> before retiring.
>
> Having AutoCad to assist with the dimensional stuff is a big plus.
>
> Carl
> KM1H
I think the original poster wanted an understanding of stripline design -
something you do not get by plugging in dimensions into expensive closed-source
'black-box' software.
The theory of transmission lines can be found in many books.
The theory behind the finite difference code I wrote, which can compute Zo for
odd shaped lines
http://atlc.sourceforge.net/
can be found in an article I wrote for QEX. A PDF can be found at
http://atlc.sourceforge.net/qex-december-1996/atlc.pdf
The basic C source code is reproduced in full - about 100 lines of it! The
version on Sourceforge is of course a lot larger than that in the QEX article.
Dave
> ----- Original Message -----
> From: "Dr. David Kirkby" <david.kirkby@onetel.net>
> To: "Roger" <sub1@rogerhalstead.com>
> Cc: <amps@contesting.com>
> Sent: Thursday, November 19, 2009 6:13 PM
> Subject: Re: [Amps] Stripline design
>
>
>> Roger wrote:
>>> I'm looking at building a 2-meter amp using a stripline with a pair of
>>> 3-CX800's or 4CX-800's, but I've not found any real data on the design
>>> (dimensions) of the actual strip line. Another possibility is building
>>> the 6 'n 2 amp in the ARRL classic amp design handbook. I also have a
>>> Henry 2002A using a single 3CX-800 with a strip line.
>>>
>>> Unlike using the tube characteristics and designing a standard Pi or
>>> Pi-L network for a given Q, I've found no information on strip lines in
>>> any of the hand books. Yes, there were a couple of amps using one and
>>> the dimensions were given, but if the design information was there I
>>> missed it.
>>>
>>> The only thing I found on the net were the download sites that appear
>>> free until you give them your information and then they want you to
>>> pay. I'd probably sign up if they told me the charges up front.
>>>
>>> 73
>>>
>>> Roger (K8RI)
>>
>> The theory and the practice do not always agree too much, but some of the
>> RSGB
>> and ARRL manuals do cover the theory
>>
>> Basically you need to make a transmission which has an equal and opposite
>> reactance to the tube. The reactance of a length l of a transmission line
>> of
>> impedance Zo is easily calculated - the equations can be found in any
>> decent
>> book on transmission lines. If you want some references, I can dig you out
>> a few
>> - I've got several on my book shelves which cover this.
>>
>> You will need a reasonable understanding of maths to follow the
>> derivation, but
>> if you only want the result, it is quite simple. It has a coth()
>> (hyperbolic
>> cotangent) in the formula if memory serves me correct, but a handhold
>> calculator
>> can compute that.
>>
>> The impedance of things like coax lines are easily found from theory. For
>> non-standard shapes, you might like to look at
>>
>> http://atlc.sourceforge.net/
>>
>> which is free and open-source finite difference software. I wrote that
>> software
>> - there is no need to sign your life away.
>>
>> It needs a Unix or Linux or Mac OS X system to run on. (That said,
>> somebody has
>> compiled it to run on a Sony Playstation!) I can't be bothered with
>> Windows. At
>> the time I wrote it, the software was very expensive in terms of CPU time
>> needed, but that will not be an issue now.
>>
>> I believe the results are very accurate for enclosed air-spaced lines. For
>> multiple dielectrics, with open structures, the accuracy drops a bit.
>>
>> The problem is that while one can do a lot in theory, the practical
>> aspects
>> means that some things can't be modeled (at least with software I'm aware
>> of).
>>
>> You can't consider a tube to be electrically small at 2m. If you have a
>> shoring
>> link at the end, you can't consider it has zero length, but neither can
>> you
>> model its effect accurately.
>>
>> So basically, while you can do all the theory, in practice it will come
>> down to
>> cut-n-try.
>>
>>
>>
>>
>>
>>
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