On Sun, 20 Nov 2011 08:16:21 -0800, Fred Abse
wrote:

On Sat, 19 Nov 2011 14:14:45 -0800
John Larkin wrote:

Lots of online calculators are available.

I use this. I'm not sure how good or otherwise it looks in Excel, it was made using Sun Microsystems' Star Office, and exported as XLS. I hope the bitmap appears in the right place to overlay the value fields, I don't have Excel, to try it.

It produces theoretically image-matched attenuators for any combination of input and output resistances and any value of attenuation. Unrealizable combinations just result in negative values.

Derived from Radiotron Designer's Handbook, Chapter 4, "Theory of Networks", Sect. 8(v) "Image impedances and image transfer constant of four-terminal networks". Equations 17a thru 17f apply. There's a neat trick to get rid of the hyperbolic functions.

I wrote it about 30 years ago, as an HP41CV calculator app, and subsequently made a spreadsheet out of it.

See attached file.


Ooh, very nice. Thanks. JF can use that to fix up his design.

John