"Ian White, G3SEK" wrote in message
...
Steve Nosko wrote:
I have the 269 HF VHF UHF analyzer and noticed something strange.
In the "non-50 ohm" Advanced menu 3 mode, with the Zo set to 75 ohms,
an otherwise good 75 ohm load (please assume I know how to tell and I
used a low frequency to reduce errors) shows something like a 1.3 : 1
SWR.
And it had correctly showed SWR=1.5 when Zo was set to 50 ohms?
Yep! An extensive sheck of known good loads showed that the MFJ was
working as expected with reasonable accuracy. I don't have numbers, but 50
ohm loads looked ok and SWR, Z etc all appeared to be reasonable. Just this
one problem. (I have access to Agilent "N" cal kits)
When I called to ask about it, the first tech at MFJ seemed confused
and clearly did not understand. Another call, on another day resulted
in a better tech, but the response was to send it in for
re-calibration. This also seems to be a calculation rather than an
adjustment, no?
Once you know Z it is a simple calculation to get to SWR for another
Zo. Or have I been smoking a bad brand...?
I didn't check this feature as part of the review, but it should be
simply the inverse ratio of whatever resistances you choose to define as
your Zo values.
Woha! I see they have on line calibration manual for the 259B & 269
on line!
http://www.mfjenterprises.com/MFJ-259Bcalibration.php
http://www.mfjenterprises.com/man/pd...alibration.pdf
I don't see anything other than "watch the blinking SWR" .(sounds like
a British insult) for the Advance 3 "calibration".
The MFJ-269 had to go back after the review (which itself was a few
years ago) so unfortunately I'm no longer able to check your findings,
Steve.
But don't recalibrate it yet, because that would be stirring-in
additional variables which will muddy the waters right now. After the
present question has been resolved, you may be able to give the
calibration procedure a little more TLC than there was time for on the
production-line - but you'll need some precision standards to do it.
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek
The problem is the I found nothing wrong when measuring in all the other
modes. Only this one problem and I believe this is a calculation in the
microprocessor, not anything that can be "calibrated" to correct. I was
asking if this is correct. I also see nothing in the MFJ cal procedure for
the 269 for this mode other than "watch the blinkin' SWR symbol" (I
indicates you have set a Zo other than 50.
--
Steve N, K,9;d, c. i My email has no u's.