On Sun, 21 Dec 2003 17:27:21 GMT, Allan Butler
wrote:

Thanks Richard;

I can understand the need to calibrate and verify everything as you said.

One of the things that popped up was your comment on making certain that the
source matches the intended load Z. When I worked on receivers in the past
we used to use what is called "hard microvolts". This was done by putting
a 3dB pad in the line between the receiver and the signal generator. That
way the impedance of the generator was more likely to be 50 ohms even though
the generator was specified to be 50 ohms.

I always remember that it was hard microvolts because it was harder to make
specifications on the radio with the attenuator in place.

Thanks for all the pointers. It is amazing that some people don't
understand that the equipment may be up to snuff, but the procedures are
blowing the results out of the ballpark.

When we used network analyzers we always tried to make the device we were
developing so it could plug into the face of the analyzer. If that was not
possible we would use cables made by the factory for that analyzer, clean
all the contact surfaces thouroughly, make certain that connectors were
torqued properly for the series and then do a full calibration at the end
of the cables so the analyzer would be able to give us results as good as
possible.

Unfortunately I don't have access to that type of equipment anymore
otherwise I would be using that.

Thanks again for the information.

Al Butler
ka0ies

Hi Al,

You are welcome. Visits to some of the Hamfests should reveal a lot
of microwave plumbing that could do all of this for you. Few who
traffic in that trade know the original cost of that stuff, and it
goes for literal pennies on the kilobuck. Then there are those who
are savvy enough to charge a healthy hunk of change - I would trust
them more for at least knowing how to preserve their investment.

Example: I recall seeing an HP Coaxial slotted line for sale at $20
and the fellow offering that the detector probe stripped from it would
make a neat depth gauge. How my heart sank....

As for your discussion about the 3 dB pad, its application is to serve
as isolation from source Z variation. It usually came in the form of
a T resistance network if I recall correctly.

Hammering out all these variables in the SHF lends perspective to what
matters, and how much, at a manageable scale that can be handled all
in one place on the bench (unlike spreading out over 10's of meters
for HF).

73's
Richard Clark, KB7QHC