WarrenS wrote: > I have been using a simple low cost, high performance alternate solution to > the standard Dual Mixer/DMTD. > The idea is based on an analog version of NIST's "Tight Phase-Lock Loop > Method of measuring Freq stability". > http://tf.nist.gov/phase/Properties/one.htm#oneone fig 1.7 > > By replacing the "Voltage to freq converter, Freq counter & Printer with a PC > data logging DVM, > It was simple enough to be up and running from scratch in minutes, > and the best part, it cost me nothing because I already had the four main > parts that are needed. > When a high resolution data logging DVM is used you don't need the offset > voltage. > To get better performance which seems to exceed most DMTD for low tau > numbers, it takes a little more work > and the use of a higher speed oversampling ADC data logger and a good offset > voltage. > > I'll also add that this is not a popular solution, > but as far as I've been able to determine it is the BEST SIMPLE > configuration, > IF you know analog and have an HP 10811 osc to use for the reference. > I've attached a Basic modified NIST Block Diagram showing what I made: > > The NIST paper sums it up quite nicely: > Using this configuration, it is not difficult to achieve a sensitivity of a > part in 1e-14 per Hz resolution of the frequency counter, > so one has excellent precision capabilities with this system. > (I'm achieving well under 0.1 ps Phase resolution, and 1e-12 at Freq > resolution with 0.1 TC, limited by my noisy reference) > > Note that the logged data is in Frequency and not Phase. > I have found Ulrich's Plotter program great for doing the ADEV graphs > > As always, Negative criticism welcome, > Have fun > ws > > Warren
You need to ensure that the isolation between the 2 sources is sufficient to ensure that locking due to unwanted signal injection doesn't significantly effect the effective VCO EFC to frequency transfer function. This method requires that the one of the 2 sources being compared can be phase locked to the other. This isn't always possible, for example, if one wishes to evaluate the stability of an offset oscillator this technique cant be used. Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
