Dave wrote:

"Cecil Moore" wrote in message
et...
I think if you will recheck that posting you will find the assertion
was that a Bird 43 cannot give valid readings by sampling at a point.
The line must be at least 1/4WL, and preferably 1/2WL, so that voltage
maximums and minimums will exist and can be measured.


i want to see a quote from a manufacturer's or good laboratory manual for
that 1/4 or 1/2 wave thing on the bird also.


Cecil was quoting someone else there, and is completely innocent :-)


Here's how the Bird 43 measures VSWR. It contains a pair of needle-fine
voltage probes, powered by small explosive charges. When coax is
connected at either side, it fires those probes out into the coax until
it finds a voltage maximum and a voltage minimum. Then it computes the
Voltage Standing Wave Ratio and a recoil mechanism reels the probes back
in. It's so slick, it all happens before you even know it.

Warning: when handling a Bird 43, keep all sensitive parts more than
1/2WL from those sockets!


An alternative possibility is that the Bird 43 does give valid readings
by sampling at the point where it physically is.


--
73 from Ian G/GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek