QRP QRSS Beacon Transmitter - on air

This article describes an on air test of the QRP QRSS Beacon Transmitter project.

Fig 1:

Fig 1 shows the project under test. The transmitter output power is measured at 100mW, the antenna is Bowral 7MHz dipole for local contacts.

W4HBK grabber

A test was run on 01/07/2012 from 0000Z to 1300Z and the results observed on W4HBK's grabber at a distance of 14,668km:

• RX TS-440 with 400Hz filter;
• Ant 30/40 trapped inverted V with apex at 20m, legs pulled out north/south, located in a small swamp behind the house; and
•  fed with 60m of RG-6.

Raw data

VK1OD showed up in just four 10min grabber frames as shown below.

Fig 2:

Fig 3:

Fig 4:

Fig 5:

The signal is fairly indistinct in each of the frames, though because the content, timing, frequency and shift of the signal are know, the signal at 7,000,820 is likely to be VK1OD.

Image stacking

The above four images with 'stacked' using Rot'n'Stack to average the signal levels across the four 10min frames.

Fig 6:

Fig 6 shows the stacked image. The images were aligned on the xx:x9 time markers at left and right sides of the plot. It is evident from the blur on the middle time markers that the Spectrum Lab images have a little error in their rendering.

The message can be read with confidence from Fig 6, it is "VK1OD =" starting at about 8s after the x0 minute. Frequency, frequency shift, message content and timing reconcile with the transmitter.

The other signals in the 'stacked' image (NU7B and WA5DJJ) are not enhanced because they are not repeated on a 10min cycle. NU7B's signal is at QRSS20 and takes longer than 10minutes, WA5DJJ's signal at QRSS6 takes less than 10min.

Key to the ability to 'stack' the VK1OD signals is that the keyer sends a message that is accurately timed to repeat on a 10min cycle.

Interestingly, in 13 hours of monitoring, the signal was perceptible in only 40 minutes of capture around 1130Z which is 0430 (1.5h before sunrise) at the receiver (Pensacola FL, US) and 2130 at the transmitter (Bowral NSW, AU), (4.5h after sunset). Propagation probably depends on the so-called grayline conditions, D layer intensity (and absorption) decreasing albeit with delayed decreasing F layer intensity at the transmitter, increasing F layer ionisation but still depleted D layer intensity near the receiver.

The 100mW QRSS transmitter was received even though the antenna is designed for local contacts, and NVIS design.

Thanks to W4HBK for the captures.

Links

• QRP QRSS Beacon Transmitter
• Bowral 7MHz dipole for local contacts
• Simple Morse beacon keyer
• QRSS observation utilities
• http://www.hanssummers.com/qrsskit.html
• http://www.etherkit.com/transmitters/openbeacon.html

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