[Meteor-Scatter] 144 MHz Es

[Keith Naylor]

Hi All,

Actually its just a little more predictable than you think.
Its within the scope of most stations to find there own backscatter 
"echo" point(s).
The opening on the 20th May from here (JO01gn) revealed 2 zones at
1400km and 3000km, a little short for most of the time to EA7/CT
and too long to EA8. (This can vary dramatically with elevation but 
thats another story).
As Graham suggests, there was probably tropo at the EA8 end but I
believe this only extends the virtual Es path by k1/k2, the ratio of the 
relative
refractive  indexes.
Its unlikely that any real reflection occurs on the sea/land as the loss
introduced would be very high at these wavelengths (can be quantified).
Its not unusual to hear stations at the intermediate skip distance, this 
unfortunately
gives the illusion that the signal has returned to earth somewhere.....
Anyway, that remains academic, whats more important is finding if the band
is "open" and to where. Being pre-warned means being well-armed to take
maximum advantage as the band suddenly opens.
To detect your own BS echo does not require any special kit other than
being able to fast switch between TX and RX.  Invariably, you do not
need high power either, 100W is sufficient on "good" days, on really 
good days
you can hear your return, on exceptionally good days there is actually 
stations to work.....
A solid-state switch is relatively easy to implement (see the SM5BSZ pages).
You need a means of generating a short "keying" tone or a gating pulse, 
in the order of 100
microseconds (10kHz), thats rather dependent on what range resolution 
you want to achieve
and what your system will support. The shorter the better as Es is very 
range critical.
The amp usually has to be keyed live using  electronic bias changeover. 
(At 300m/us *2 you
calculate the necessary delay times, I use a sound card and Spectrum 
Lab, but this may
cause problems with the latest modern rigs due to inbuilt TX/RX delay 
mechanisms).
You can process the received return either directly on a scope triggered 
from your
TX pulse or run the output into a sound card and timer. No AGC on RX.
This is not rocket science and this method has been used for plenty of 
years here, mainly
for F2 on 6m.
There was a full  description in QST many years ago (W5FF was the author 
I believe),
I am sure there is a copy somewhere on the web archives.
If you intend to go down this road I would suggest quantifying your RX 
system first, that
is the delay time through your RX  from antenna to audio output. Modern 
DSP radios
screw up totally in this department as do noise blankers that are 
"active" all the time (i.e.
un-modified FT1000's etc).
BTW there are at least 7 recorded Es incidents of OK1 to EA8 since 1982 
and no doubt
a lot more, this particular path is relatively common.
Finally, to work Es succesfully, there is absolutely no substitute for 
being behind the radio
and your finger on the dial....

73's
Keith G4FUF