An additional source of error is the fact that the 5000 does not tune
continuously. It tunes in steps, and they are irregular, so an
additional correction is required. When you are watching your WWV
phase display, a part of the error you see may be due to this. This
may not be important unless you are trying for sub -100 mHz accuracy.
Jerry W4UK
At 07:12 PM 10/9/2010, AA8K73 GMail wrote:
Hi Jeff,
For about $150 you can get a used Trimble Thunderbolt
GPSDO that will give you a precision 10 MHz reference
signal to put into your Flex Radio. Tune in WWV
and watch the Phase display. The rotation is from
Doppler.
After parking the rig at a convenient frequency a
couple of hundred Hertz below the signal of interest,
I use PowerSDR to record a receive post-processing
USB wave file while the test is going on.
I run the free Spectrum Lab software while playing
back the wave file and watch the signal on the
Spectrum Lab waterfall. You can see it wander in
frequency when the propagation changes. Add that
audio frequency to the frequency displayed in
PowerSDR. I make my best guess for the middle of
the Doppler swings and send it in.
My PC is nothing special, just an AMD Athlon 64
2 GHz and Windows XP. Oh, and download the free
Lady Heather software for monitoring your
Thunderbolt. An awesome program.
The ARRL FMT is on November 10th. Join the fun.
It's not about reading to the milli-Hertz; it's
about developing your skills in frequency
measurement.
Mike - AA8K
On 10/09/2010 06:14 PM, Jeff Singer wrote:
Thanks for the alert on the K5CM Frequency Measuring Test a few nights ago.
That test uses two stations to send a CW carrier on 160, 80 (twice) and 40
meters. A FMT is something totally new to me. My only preparation was to
calibrate the radio carefully against WWV using its built-in scope. My
receiver was in the DSB mode. I used the scope to guess-timate the frequency
to an additional decimal point.
Few entrants use a radio alone. Many have costly GPS based frequency
calibration sources or the like and complex schemes to interpret the
frequency. Experience counts. So does speed, since you only have three
minutes to come to a conclusion. In other words, my entry wouldn't threaten
the experts who come within one or two MILLI-hertz.
But my stock Flex did very well. Three of my four readings were within 1/2
Hz. On 40 meters I was off by .96 Hz. QRN on 40 made the weak signal
difficult to read on the scope. Still, accuracy was better than .25 PPM on
each reading, well within Flex specs. Anyone else participate?
Jeff K0OD
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