In the summer of 2011 I got together with Bill W4HBK and started testing for the lowest power needed to communicate a message (my callsign WA5DJJ) between my location in Las Cruces, New Mexico and his location in Pensacola, Florida. This time we were going to try a new to us technique of precision timing of the transmitting call sign using the standard 6 second dits modulated as QRSS FSKCW and a technique of stacking 10 minute grabber frames to build a composite picture. What this essentially does is enhance the signals and de emphasize the noise. It is a technique that is used by the astronomy buffs to enhance their star pictures to brighten very dim stars in their CCD captures. The first test was run at 250 mW power output from my transmitter. (The transmitter is both crystal oven frequency stabilized and the keyer uses an exact repeatable software program written by N0QBH) The following screen shots are the results of our tests. This test takes some weeks to perform as we also had to wait on good propagation between the two sites.



These screen shots were put in here to show you the difference between the Raw Data and a Stacked Image.

The above screen show is the raw picture showing my call sign along the bottom of the screen shot at 40mW power level.

The screen shot below is essentially the same image but stacked with 4 or more similar 10 second screen shots to enhance the signal presence. The signals that are transmitted on an exact 10 minute schedule will be enhanced. The ones that are not transmitted on that schedule are not. The signal at the top is P29ZL from Papua, New Guinea who is stabilized. Signal with the triangles is not 10 minute scheduled and you can see in the stacked image that the triangles run together and become unintelligible in the stacked image. The image above mine at the bottom is Chris WB5FKC who is both stabilized and using a modulation technique of Differential Frequency Shift Keying (DFSK). As you can see the weaker signal in the raw data was made very readable in the "stacked" image.


100 mW TEST


This image was at 100mW and was so clear that we didn't need to stack the image to prove it was me. The propagation was better this day than it had been so the 100mW test went quickly.




We stepped quickly through the steps between 100mW and 100uW and the pictures were essentially the same for the stacked images. Here Bill W4HBK annotated the signals in this "stacked image. My power level in this screen shot was 100uW (Yes I said 100microwatts or .0001 Watts)




48.8uW TEST


This is the stacked image for 48.8uW. At this time I had broken my previous record of 65uW for the path between us that I had accomplished in the 80 second test. As you can see, The call sign of WA5DJJ is clearly visible in this screen shot. Now to decrease the power some more... 23.9 uW (The reason for the odd numbers down here at this range is the difficulty of making fine adjustments in the transmitter power)



23.9uW Test


This is the "stacked Image" of my signal at 23.9 uWatts. We are getting a lot of noise at this level and the stacked images are not as clean as they were earlier. But My call sign is still clearly visible along with others on the page. Some of the dynamic range is also lost as some of the signals are clearly much stronger than mine and may be distorting the image. Some change in stacking techniques may be required to help pull my signals out of the noise. The test is continuing at a power level of 8.51uW. We are getting down to the ESP Level now.


8.51uW TEST


This is the "stacked image" of my signal at 8.51uWatts. My signal is clearly visible using 12 of the grabbers 10 minute images (that is 2 hours of copy or 120 minutes). W4HBK said that it was visible on the 4 Hour grabber image for quite some time so the propagation between Las Cruces, NM and Pensacola, FL must have been very good at these low power levels. A screen shot of the 4 hour grabber is shown below and if you look along the 10,139,915 Hz line you will see my signal is visible for almost 2 hours off and on.

So, The quest continues. The transmitter is now at 3.89uWatts. We are watching for another bubble in the 30M propagation. Hopefully, we can add another power reading or two to this website before the little FSKCW signal can no longer be seen.


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