Round the World

Home ] Up ]


Click HERE for the Amazing Online Ham Radio Flea Market

Click to Buy and Sell Ham Gear Online





6.7m fibreglass poles for sale click ***HERE***

  Search G3CWI's site

Summits on the Air - click here


It is not uncommon for signals to go right round the world - often several times. The following plot shows round the world echoes from the Inskip transmitter about 80km from me on 9 December on 25MHz. The bottom line at 0ms is the ground wave, from about 0830 until 1600, the faint trace at 10ms is backscatter. The really interesting return is even fainter and is the horizontal line at about 138ms running from 0900 to 1100. This is a round-the-world echo from Inskip (40,000km).

25MHz RTW 9 Dec 2002.bmp (160254 bytes)

The following plot was done on the previous day by Peter PLX and Andy G0TJZ/P. Peter was transmitting Chirps and Andy was receiving them. The first response is the groundwave, the second is backscatter and the third is the RTW echo - there is a timing offest in the system so it does not appear at the usual 138.5ms. One of the interesting charactersitics of RTW echoes is how little spread there is in them, suggesting strongly that a single mode of propagation and path is responsible for the effect. On a good day it is quite possible to see 1RTW, 2RTW and even 3RTW with just a 100 W transmitter!

wpeD.jpg (41930 bytes)

The following plot from Peter Martinez shows 3RTW (just!).

wpeD.jpg (33983 bytes)

An experiment is being run at the moment to attempt to understand how focussed the RTW returns are.

Here are some results that I received on 16th December using RTW software by Andrew Senior. The test signal was a special chirp transmitted by Peter G3PLX on the 24MHz amateur band (100W transmitter and vertical antenna). The signals were received using a standard amateur receiver and a doublet antenna. The plots show that groundwave is received, followed by some backscatter then the first RTW echo, followed by the second. I could occasionally see 3RTW too but that was too weak to reproduce here.

1RTW example.bmp (456054 bytes)

1RTW and 2RTW.bmp (456054 bytes)



Home ]