On Tue, 09 Aug 2005 21:48:00 GMT, "SignalFerret"
wrote:

Just curious, what is a piston attenuator? For the life of me I can't seem
to picture it. I know how a slab of resistive material inserted in to a
wave guide works as an attenuator, but how is it accomplished in a coax
transmission line? If someone has a photo, or diagram of the inner workings
that would be great!

Hi Robert,

It is a "below wavelength cutoff attenuator." It is basically two
coupling loops put in a conductive tube the size of a toilet paper
roll. One loop is movable on the so-called "piston" (although the
resemblance ends there, no compression is expected). At the other end
of the "cylinder" is the other loop. As you draw away, or closer, the
attenuation is linearly variable to quite a high degree.

Of course, all other provisos still apply.

There are far more step attenuators than these, however amateurs like
doing simple things difficultly. If sealing the box of the stepped
attenuator was difficult, I can imagine the fun of circular seals.
Nothing precise nor accurate is required for RDF - but low leakage
does win at the end of the day.

73's
Richard Clark, KB7QHC