[Lowfer] Analog VS SDR LF comparison

[Douglas D. Williams]

Next comparison will be frequency stability. Most weak signal LF modes
depend on highly accurate frequency stability and precision for both
transmit and receive.

Not having any sophisticated test equipment, my methodology is simple. I
tune to WWVB and watch the signal on Argo for any frequency drift.

IMO, any receiver stable enough for QRSS60 is "stable enough" for 90% of
all QRSS work. Well, I went one better and set Argo to QRSS120. From the
top to the bottom of the Argo screen captures represents about 3 Hz. From
the left to the right side is about 3 hours.

I let both receivers warm up for about 20 minutes prior to starting the
screen captures. The AMRAD LF converter I leave on pretty much all the
time, so it was already warm. As you can see on the left side of the screen
captures, 20 minutes was not long enough for either receiver to finish
warming up. In fact, it took almost an hour for both receivers to
completely finish their "warm up" frequency drift. This is in a temperature
controlled environment with central heat and cooling.

Once the one hour warm up was complete, at approximately 14:32 on the
screen captures, it becomes quite obvious that the Winradio receiver is
more stable. With that said, both systems are quite stable enough for
QRSS120. The Winradio has almost no discernable drift on the screen capture
after the initial warm up period. The R75 + converter seems to only drift
about a tenth of a Hz up and down over the three hour period, after the
initial warm up.

Note that the R75 has the CR-282 high stability oscillator option, and the
AMRAD converter also has a large OCXO. In my opinion, most of the drift of
the R75 + Converter is from the R75 itself, rather than the converter. I
could confirm this by testing the R75 without the converter, and may do so
later on.

R75 screen capture:

https://dl.dropbox.com/u/33457409/R75%26Winradio%20Comparison/R75QRSS120.jpg

Winradio screen capture:

https://dl.dropbox.com/u/33457409/R75%26Winradio%20Comparison/WINRADQRSS120.jpg



And here are a couple more captures after the initial warm up period has
scrolled off the left side:

R75:

https://dl.dropbox.com/u/33457409/R75%26Winradio%20Comparison/R75QRSS120%282%29.jpg

Winradio:

https://dl.dropbox.com/u/33457409/R75%26Winradio%20Comparison/WINRADQRSS120%282%29.jpg


Conclusion:

The Winradio Excalibur Pro is the clear winner in stability, but the R75 +
Converter combo is plenty stable enough for QRSS120 or "faster".

Since the latest build of Argo also includes both QRSS600 and QRSS1200
modes, it would be interesting to test the Winradio Excalibur Pro to see if
it would be stable enough for either one of those modes. Perhaps I will
later on.

-Doug KB4OER


>
>