On 24 August 2013 18:55, Joseph Gray <[email protected]> wrote: > David,
Hi Joseph > That is quite a difference between the two certificates. The Techmaster one > doesn't tell you anything about what they actualy measured, or the > uncertainties. You have to trust that they know what they are doing and > that they actually did it. I think Techmaster certificates are useful to T+M dealers, as they can sell things for a higher price. Their certaificates are also useful to end users that just need a certificate to satisfy some institute or body. But I don't believe it would satisfy a competent engineer who really wanted to know if the instrument was working properly. A competent enginner would not be too conviced. When an Agilent VNA calibration expert (Ken Wong) wrote on the Agilent VNA forum that "I will be very skeptical when a VNA calibration service does not include a cal kit and verification kit." and that Techmaster cal certificate did not use a verification kit, one has to be sceptical. The fact Techmaster also issued a cal certificate for a calibration kit makes me suspicious too. Apparently you need access to primary standards to verify they are in spec. There is something else interesting on that Techmaster certificate. Note it says "option 010 added". That is a software option (enables a Inverse Fourier transform to convert frequency domain data to time domain). It is no longer sold by Agilent. I do wonder if that was legally added. Buying that option for a new VNA costs several thousand dollars, but the 8720D was last made in around 1999, and has been unsupported since 2004. I suspect these cal labs are useful for things like getting software options added! Agilent will certainly not sell the option. > With the Agilent certificate, there is data to > give you confidence that things were done properly. Yes. Note the Agilent calibration is not acreditated by anyone. I could have had an acredited calibration, but I did not want to pay the extra 50% or so. From what I understand, the VNA would be calibrated in exactly the same way. But it costs Agilent money to get acredited for the calibration, so they pass that cost onto those that want it acredited. For me personally, I trust Agilent know how to calibrate VNAs. There is going to be more VNA expertese in Agilent than arguably any other institution. > Thanks for posting those. It was educational. I'm glad you found it useful. > Joe Gray > W5JG Dave, G8WRB _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
