Tag Archives: doppler

VHF and UHF beacons VK2RSY recorded while mobile

On a trip to Sydney I checked for the VK2RSY beacons on 28.262, 144.420 and 432.420 to see how far out I could hear them.

I was surprised to find I could hear the 28 MHz signal at Sutton Forest and within a few km the 144 MHz beacon was also clearly audible. The 432 MHz beacon was very weak at that point but in the next 20 km it became quite readable. It was interesting to compare the signal levels from these beacons over the next 100 km or so of my trip. The best signal strength from the 144 and 432 beacons was at the start of the downhill slope on the highway just after Mittagong, heading towards Sydney. At that point the 432 MHz beacon signal strength indicated S5, with the preamp ON.

On the way back home from Sydney I recorded the beacon signals and the files are available here, in both MP3 and AMR format. I used a Nokia mobile phone to record these signals – not the most elegant recording method but it’s a start. If you have software to play or convert the AMR format, the AMR file format produces more compact files. I used Miksoft.com’s converter to produce the MP3 versions.

Recording 1 of VK2RSY on 432.420 and 144.420 in MP3 format 1.4 MB – 1 minute, mostly the 432 MHz signal but at about 15 seconds you hear the improvement in signal strength and quality when I switched over to the 144 MHz signal and then back to the 432 MHz signal a few seconds later. AMR format 42kB

Recording 2 of VK2RSY on 432.420 and 144.420 in MP3 format 1.4MB – 1 minute – starts with the 432 MHz beacon and at about 20 seconds, I switched to the 144 Mhz signal and back again. AMR format 42 kB.

I was struck by the apparent change in quality observed when switching between the beacon frequencies. When I was stationary, both signals sounded clean and pure. While mobile the 432 MHz signal showed considerable multipath and smear like a 10 GHz sigal with doppler or rain scatter. I am not sure exactly what caused that effect on this signal . Apart from the blur or smear of the signal there was also at times a second version of the signal on a slightly different frequency, which I assume was an aircraft reflection with doppler shift.

I was asked why I didn’t also check for the signal from the 6m beacon on 50.288.  This was an obvious omission from this experiment and I did have a 6m antenna I could have substituted for the 10m helical.  Something to try next time.  I’ll also try to record that doppler effect signal.

This post was originally set up as a “page” but in a redesign of the site I decided it should be a post instead.