On Wed, 22 Dec 2004 00:19:12 +0000, Ian Jackson
wrote:

The point I was trying to make was, if the L-pad was 'not the best
design for a matching network', why are there so many about?
It gives the minimum loss for a match in both directions (with the 43and
86 ohm resistors). What works better?
Ian.

Hi Ian,

The topic is Why Match? and the context is with bench gear,
specifically a Spectrum Analyzer. It is pleasing that no sardonic
quips as to this device's suitability for antenna matching has sallied
forth. Attenuators serve a limited purpose - Isolation. They serve
this well when they don't introduce uncontrolled error. They also
serve as range extenders as do directional couplers, often with
attenuators paired with them.

In the case of using them with couplers, they insure port isolation by
insuring port loading. They buffer any deviance from an expected 50
Ohm load that may be presented by monitoring gear attached through
them to that port. This is by and large the context of the mini
circuits links you offered. The extent of this "insurance" can be
observed by computing how much load is presented to the affected
instrument when the attenuator is left open, or shorted. T or PI
configurations show a higher tolerance. An L Pad is a special case
(less general form) of either T or PI, being that one of the three
elements is replaced with either a short or an open.

73's
Richard Clark, KB7QHC