Todd, you already have sent me the appropriate SelfCAL circuitry, but I did not recognize (understand) it as such! I also received a hint from another volt-nuts, John, about the complete documents for the DATRON 1271 on the KO4BB site, which is very similar, and also contains a SelfCAL module, being a bit different than the one inside the 1281. The schematics for the 1271, anhow reveal how the transformer inside this module provides different voltage ratios. The transformer there is labelled +9.93V, +/-7.23V (that's the main references value), 1.83V, 1.00V and 0.19V. These ratios were generated with a precision switch mode / chopper circuit, and as the ratios on a transformer are very stable, you only have to measure them once during initial calibration. Obviously that is good for ppm ratio accuracy in the SelfCAL procedure. So thanks again Frank

No problem. I was just looking back at the documents wondering if I missed anything. The transformer solution is interesting and I see that the 8508A has a second low voltage transformer (T1). I have no idea if it performs the same function using a different calibration. On Sat, Oct 31, 2015 at 9:33 AM, Frank Stellmach <frank.stellmach@freenet.de > wrote: > Todd, > > you already have sent me the appropriate SelfCAL circuitry, but I did not > recognize (understand) it as such! > > I also received a hint from another volt-nuts, John, about the complete > documents for the DATRON 1271 on the KO4BB site, which is very similar, and > also contains a SelfCAL module, being a bit different than the one inside > the 1281. > > The schematics for the 1271, anhow reveal how the transformer inside this > module provides different voltage ratios. The transformer there is labelled > +9.93V, +/-7.23V (that's the main references value), 1.83V, 1.00V and 0.19V. > > These ratios were generated with a precision switch mode / chopper > circuit, and as the ratios on a transformer are very stable, you only have > to measure them once during initial calibration. > > Obviously that is good for ppm ratio accuracy in the SelfCAL procedure. > > So thanks again > > Frank > > > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. >

On the subject of the Datron/Wavetek 1281, the one I received did not have a calibration key. It did have a jumper wire connected across the cal switch which I would like to remove. I want to keep it in its original configuration if possible. I do have keys for the Datron 4700 but the key does not fit. There is a seller of a Datron 1271 that is including a key and I may have to contact them for a copy if I cannot find one from a local volt-nut. If anyone has a copy to sell, I would appreciate it. Thanks, Todd