The other night I had a conversation with Ernie (VE3EJJ) about spectrum analyzers, etc. and he asked if I had tried tuning in CHU or WWV on the spec. an. yet. Sheepishly I said “no,” having never thought to undertake such an endeavour.
By tuning a transceiver to the appropriate frequency (~3.33MHz USB for CHU), it is possible to “zero beat” your transceiver to determine the frequency accuracy of your radio. The process is similar to tuning a guitar while plucking two strings which are harmonically related. A “beat frequency” will exist while the two tones are not identical – the closer in frequency the tones, the lower the beat frequency. A beat-tone sounds like a gradual quietening and loudening of a signal.
In my case, using a spectrum analyzer with the appropriate settings will allow an observer to actually see where the transmission occurs in the radio spectrum. By narrowing the span which the spectrum analyzer will sweep, one can obtain a very favourable receiver bandwidth (RBW) to very accurately determine where the peak of the transmission occurs. In the case of CHU, it was found to be at 3.330000MHz which indicates that the internal standard in the Rigol DSA815-TG is extremely good. I would like to repeat this experiment with an atomic standard or a GPSDO (GPS disciplined oscillator).
Testing for frequency accuracy higher in the spectum, I tuned the spectrum analyzer to 10.000000MHz which is where WWV can be found. Again, the frequency accuracy of the DSA815-TG was found to be extremely good as the signal of interest was seen to peak at 10MHz on the spot. Using a 10Hz RBW and a 1kHz span with trace averaging, I confirmed the results as indicated.
Although I still would like to have a 10MHz frequency standard for the lab, the above results have helped to push the RbDO further to the back-burner for now. I am continually impressed with this little spectrum analyzer!