Sometimes static plots don't convey some of the information that a more dynamic presentation shows. After a lot of effort spent wrestling with file format conversions, I finally managed to get an embeddable video of the phase display of the Flex 5000 PowerSDR program. So here is a movie of the WWV 20 MHz signal phase and amplitude. The display is a polar plot of the signal, with the radial direction giving the amplitude of the signal and the angular coordinate showing the phase of the signal.

Some comments in regards to the Flex display limitations. First the frequency of the radio can only be set in 1 Hz increments, which means that it is difficult to remove frequency mis-tuning rotation of the phase. For example if the actual frequency differs from the tuned frequency by 0.5 Hz, the phase point will rotate at a rate of 1 rotation in 2 seconds. Luckily in this case the discrepancy is much less, so that there is little net rotation except that due to intrinsic phase variations.

The display is the "Phase" selection in the display options on the PowerSDR, which means it is after the detection process. I have set a 20 Hz wide filter centered on the carrier frequency, so we are seeing only the carrier portion of the WWV signal. I needed to set the detection mode to DSB (double sideband) to get the signal display I wanted.

Also for some reason the PowerSDR evidently only displays a portion of the time course of the phase. It appears that it samples two discontinuous portions of the signal to display, so there is a choppiness to the phase points that are displayed. I do not know what portion of the signal is shown, nor do I know the reason for this selection.

Despite these limitation, this is still an informative display. The signal is relatively stable and strong, as you can see from the video. There is only one occasion in which the signal disappears and the phase jumps across the display through the center. This event corresponds to those points in the graphs in the previous posts where the phase jumped by some amount when the signal strength dropped. Also to be noted is that phase wrap is intrinsically not an issue here because the rotation angle wraps around naturally at two pi.

Over most of the time the phase is stable to less than pi radians, though near the end it rotates through almost two pi. This translates to a frequency stability of about 0.02 Hz : the signal path between Boston and Colorado was pretty calm when this was recorded.

With this real-time display it is easy to get an idea of the detailed stability of propagation on almost any signal that is received. It gives another dimension to the perception of propagation conditions affecting a particular signal, and signals on the same band can be quickly observed to get a feeling for more general propagation.

Tangled Spaces