"Cecil Moore" wrote in message
om...
Dave wrote:
"Cecil Moore" wrote:

Owen Duffy wrote:
This has nothing to do with the stated myth: Measurements with a Bird
43 of the conditions on the Thruline section are invalid unless it has
some minimum length of 50 ohm line on both sides of itself.

Would you be willing to make the same statement about an MFJ wattmeter?

now your are just trying to muddy the waters... i wouldn't trust an mfj
to measure anything!

No, I'm just trying to get back to the original discussion which
was: Do SWR meters need 50 ohm coax surrounding them to establish
the assumed 50 ohm environment? The majority of SWR meters have
no Thruline and MFJ seems to make no attempt to establish a 50
ohm environment like Bird does. What is the Z0 of a meandering wire
surrounded by an aluminum box?

The original discussion (V/I ratio is forced to Z0) had nothing to
do with Bird wattmeters. The original discussion was about SWR meters
in general (which the Bird is not). The mythbusters thing was an
interesting diversion away from the original question which remains
unanswered.
--

an interesting diversion until everyone was convinced that you were off the
wall. now its time to re-open a dead thread???.

as far as cheap swr meters, the daiwa, swan, and mfj manuals all require 50
ohm coax 'for accurate readings'... a joke by any standard of measurement
for that type of instrument. but just to put this one to rest quickly... i
set up my tdr and ran some quick measurements. this tdr will resolve a 6"
75 ohm jumper in the 25' or so of 50 ohm test cable that i used. i measured
an mfj-815b and a daiwa ns-660pa and they are indistiguishable from the 50
ohm line. so the answer is yes, they do internally look like a 50 ohm line
section.