I have built a design out the ARRL handbook using a toroid transformer,
and SM 100 ohm resistors in parallel to make up the 50 ohm sections. I
could get 40 dB return loss to about 50 MHz, when matching a 50 ohm
load. This gives an idea of the accuracy of your bridge, ie the higher
the return loss in this situation, the better the bridge, assuming an
accurate 50 ohm load. I used a spectrum analyser as the detector and the
venerable HP8640B for the source.
You can even measure small inductances (I got reasonable accuracy to
about 100nH) using a series RLC combination on the end of a length of
coax as the unknown load. (ie do it remotely!) R=50, C=is known, L is
unknown
At some frequency there is a max return loss. At this freq XL=XC and
X(LC)~0, assuming perfect components. Thus the load is 50 ohms. You can
work out L knowing C

Richard

Henry Kolesnik wrote:
Does anyone recall seeing an article for constructing a return loss bridge
in RF Design in late 80s or early 90s? I'd like to see if I can get a
scan, I've been bitten by the RLB bug.
tnx
Hank WD5JFR