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"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. |
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