Hi Razvan
Thanks! I hadn't seen AN215 so I'll give it a good read through.
To be fair, I'm still not sure if the the 1830A is better than the N432A or the other way around. There isn't enough technical data available to make a valid comparison. However, I suspect that any differences will be tiny either way.
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In case anyone hasn't tried doing DC substitution with the old HP 432A I put up a quick youtube demo in the link below. Sorry, there's no audio from me but you can see that I have set up three 6.5 digit DVMs and linked to them via GPIB and used them to monitor the connections at the back of the HP 432A. I can then semi automate the process and I also control the 1mW 50 MHz source on the power meter.
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The V0, V1, Vcomp0 and Vcomp1 voltages are measured along with the recorder voltage.
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The Agilent 34401A meter is just measuring the recorder output and the two Keithley meters are connected for DC substitution. They both agree within one or two LSDs when on 6.5 digits so I think it's OK to use two meters here.
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I added some message boxes to the Excel sheet to help explain what is going on and I also log all the voltages including the recorder voltage at the back of the 432A.
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You can see how repeatable the readings are as I cycled through the process several times. I've not had to adjust the 1mW reference in the Anritsu power meter for something like 9 years now. In the last 8 years it has never been worse than +/- 0.01dB according to the 432A using DC substitution. You can also see how close the recorder is when the cal factor is set to 98%.
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Sorry but the video is a bit dim and fuzzy but I think it is OK for a quick and dirty demo.
Regards
Jeremy
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