[CQ-Contest] On Echos and LDEs

Clive Whelan clive at gw3njw.fsworld.co.uk
Thu Nov 1 00:24:33 EST 2001

Heino Jukka wrote:

> Back Scattering. When you send a signal it may echo (bounce back). Echo
> is about .1 secs or less. It is reasonable to expect that if you get an
> echo, then conditions for getting a qso to that direction is possible (if
> there are someone ready, HI). Some kind of "condition radar". Used much at
> higher HF and VHF; needs fast transmit-to-receive switch, fast AGC,
> reasonable power (and directional antennas).

Actually you don't need high power or a gain antenna to hear your own 
backscatter echo, but certainly good QSK is a prerequisite. That said, very 
good conditions are required to hear this from 100 watts and wire/verticals, 
on 21Mhz and exceptionally on 28Mhz. Nevertheless it is a frequent 
occurrence here in sun spot maxima.

For me the most outstanding event was in the CQWPX CW of 1999, where in 
midsummer the grey line pointed directly into South America in the evening. 
I have notes in my ( TR) log detailing precisely when it started and 
finished. Later that evening KL7 and KH6 were worked with ease around 
midnight and at the same time HL was also worked with 100 watts and a 
doublet at less than 30 ft a.g.l. Of course at that time of year, it hardly 
gets dark at our latitude (about 52N) which is more northerly than any part 
of the contiguous U.S.A., and about the same as VO1 I think.

> Real LDE, delays in seconds,

In 40 years I have only ever experienced this once, and that was about 3 
years ago on 3.5Mhz, with a delay such that I heard my complete callsign at 
about 30 wpm, probably about 1-2 seconds? Why this should favour a much 
lower frequency I have no idea. However it certainly implies that much less 
e.r.p. is involved than for backscatter or round the world echoes. The 
parallel seems to be with VHF ducting which similarly requires only low 
power. Whatever the mechanism, it certainly was a really  weird experience!


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