An A/B comparison on 40m over a 14,700km path using QRSS

This article reports an experiment to compare two nearby transmitting systems on 40m over a 14,600km path using QRSS.

The receiving station was W4HBK. The web page displaying his grabber image contains no data on his receiving system, but gives his location as Pensacola, FL (USA).

The two transmitting stations are about 18km apart about 100km S/SW of Sydney (Australia):

Both stations were using 5W of RF output power, and A1 QRSS telegraphy using a Simple Morse beacon keyer with a quite standard transceiver in CW mode adjusted for 5W of output using an external power meter.

Fig 1:

Fig 1 shows the modelled pattern of both antennas at 8° elevation (the path angle for best signals over the circuit), red is VK2DVK and blue is VK1OD. The circuit azimuth angle is 77° (13° on the chart coordinates) and the gain of VK2DVK's antenna is about 2dB higher. These figures do not include feed system losses.

Grabber images


The following images were from the W4HBK grabber. They are not time continuous as about one third of the grabber images were corrupt, but these four images were from about one hour after the path had 'opened'.

VK1OD is on 7039.850kHz, and VK2DVK is on 7039.870kHz.

Note that the graph on the right hand side is a near instantaneous condition, and a single capture of that type is somewhat limited. The 'waterfall' display to the left is more useful in forming a view of performance over time with propagation variation.

The grabber is obviously subject to lots of interference (the vertical stripes), but the capture in this interval was less affected than earlier when neaby data services were causing large receiver gain reduction (by AGC), evidenced by the noise moving left off scale in the right hand plot.

Fig 2:


Fig 3:


Fig 4:


Fig 5:

Figs 2-5 show the signals to be fairly similar, VK1OD might have a small edge slightly more often, but it would be difficult to assert that one station was 3dB better than the other on the basis of these charts.

Results could be quite different in different directions and different path elevations, and possibly at different times.

Signal strength usually improves for a couple of hours after this capture, to the point that 100mW can give modest S/N ratio, see QRP QRSS Beacon Transmitter - on air.


The following grabs were the best ones from the next day, conditions were a little poorer. This time, VK1OD is at 7039.905kHz and VK2DVK at 7039.895kHz.

Fig 6


Fig 4:

The grabber setup denies evaluating S/N with much accuracy in this experiment, in the grabs above the noise is off scale in the right hand plots.

Links / References


Version Date Description
1.01 22/09/2012 Initial.

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