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137 kHz (Read 705 times)
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137 kHz
04/09/11 at 18:15:28
 
Attached is a capture made here on the night of April 6.  Time shown is Central Daylight, and the 800 Hz mark is intended to be 137.780 kHz.  In actuality, the receiver was warmer than when I did the calibration of Argo a few days earlier, so everything is showing high by about 120 mHz (yes, that's lower-case "m" for millihertz, not mega--an important distinction in a world of digital modes); a.k.a., 0.12 Hz.
 
At top is VE3OT, on 137.7804 kHz, beaconing as "MP" in QRSS30 but with shortened spaces compared to dot length.  Right below it is WD2XGJ as XGJ in QRSS60.  Finally, down at 137.777, is VO1NA sending "NA" in DFCW mode.  (Differential Frequency CW uses the lower frequency to indicate a dot and the upper to stand for a dash, while carrier off is denotes space(s) between characters or words.) More about the signal characteristics and how I got them all on screen....
 
The screen capture below includes reception in two modes.  The five minutes at the left (wider spaced 60-second tick marks) were at 30 seconds mode and normal speed, while the right hand 46+ minutes was in 30 seconds slow.  I started out in normal speed because I was specifically looking for MP that evening, but when I realized that had to be XGJ below, I switched to slow in order to be sure I could fit in all of the ident into the window.  For those unfamiliar with Argo, the "mode" settings are optimized for different dot lengths commonly used in QRSS transmission, but there are also "speed" variations (normal, slow, or fast) in how the processed information can be displayed on the screen.
 
Now, 30 sec. slow is very similar but not identical to 60 sec. normal.  I figured it might be the best compromise to display XGJ in all its glory, while still keeping MP recognizable.  Even at that, the short-spaced characteristics of MP's keying could pose problems in identifying true spaces from the (comparatively) dead gaps caused by static crashes.  Fortunately, however, the sheer strength of MP's signal provides a clue: look for the "dog bones," the keying artifacts revealed by the spectrum analysis routines at the beginning and end of each key-down interval.
 
A couple of minutes to the left of the "X" in XGJ is what looks like a shorted dot.  This was actually Warren's 8 wpm CW station ID, which was clearly audible in the speaker.  Both MP and XGJ were strong enough to tell when they were on or off, although being so close in pitch, you couldn't have distinguished which was which by ear.  When both were on, there was a slow beat note between them, of course.
 
The NA capture was serendipitous.  I've captured it a few times before, but hadn't seen anything earlier that evening apart from a few faint traces.  I left the Argo window "tuned" to include that spot, though, just in case.  Ionospheric fading is apparently far more of a factor over the path from Newfoundland to Kansas than it is for either Ontario or Massachusetts to here.  Such is fate, however, that Argo reveals single the strongest detected signal in the image to be from NA, albeit only for a matter of seconds, during the transition from dot to dash in the farthest left letter "A."
 
You never know what to expect in radio.  Cool
 
John
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small06Apr0022.jpg

John
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