29 Apr 2015


G3WKW (134km) was spotted yesterday on 6m WSPR.  I am pretty sure I can only get a path to Bob via aircraft reflections and I think it was aircraft approaching London Heathrow. Although I copied Bob's 5W I did not get spotted by him, although I am using a lower ERP and my signal was probably in the noise at his end, if indeed he was listening/looking.  Bob's 5W was around -24dB S/N with low Doppler. Of course, with aircraft, the WSPR software may not have decoded a stronger signal with more Doppler or more multi-path. It is not uncommon to see reflections from many aircraft in a single WSPR burst. Often decodes are impossible unless aircraft flight patterns result in low Doppler.

In this regard, WSPR may not be the best mode. Also WSPR TX bursts are nearly 2 minutes long and this is a long time with passing planes. Other digital modes with shorter TX bursts are probably better. In this regard, passing planes are more like MS bursts so modes well suited to MS would be better.

1 comment:

G3WKW Bob said...

Well I have to admit that when you spotted me I had not been listening because for the previous hour the %Tx had somehow been stuck at 100! How that happened I do not know. Put it down to change of WSPR version use of touch screen PC and remote over LAN operation that I did not notice. So I must have made 30 transmissions and perhaps at 10 watts before you spotted me the once. I think for it to be aircraft reflection it needs to fly along the path or parallel to it else the Doppler will be too great. When on 10 metres I have often seen strong traces fro G3JKV in Dorking but not decoded because of the strong aircraft reflections.