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CONGRATULATIONS!!!!!!!!!!!!!!!!!
FROM 0.01KM ON EARTH MODE SOME MONTHS AGO NOW YOU
WENT ON 3.6KM!!!
73
SV8GXC
----- Original Message -----
Sent: Monday, June 21, 2010 7:55 PM
Subject: LF: Earth mode DXing today -
3.6kms!
MODS TO THE SYSTEM
Some significant steps
taken with my local earth mode / induction tests today, which I'll summarise
here. Spectran screen captures will appear on my earth mode web
page tomorrow.
- Firstly, having installed the K1EL keyer chip, I decided to use its
internal 800Hz sidetone oscillator, after a bit of LP filtering, to drive my
4W PA. This arrangement now allows me to run either QRSS3 or 10wpm CW
beacons on 800Hz at the flick of a switch. It is more stable than the
external twin-tee oscillator I was using and is perfectly suitable for QRSS3
at audio frequencies.
- Secondly, I modified my loop/preamp to have marginally better
sensitivity at around 700-900Hz.
- A quick "by ear" test with the switch in the 10wpm position and the
0.5km range I'd managed before was achieved using the 80cm loop and the 20m
baseline earth electrodes.
QRSS3 DX
Now here comes
the real fun. At this point I decided to take my loop, preamp and
laptop equipped with Spectran out into the field to see what I could see/hear.
- My first location was a field 0.75km south of the QTH just out of
the village. Although nothing could be heard, the QRSS trace was solid on
the screen.
- Next step was to proceed further south along the Heath Road out of
Burwell (QTH JO02dg) to a point 2.5km away from the QTH. Again, with
Spectran, a good signal was visible on the screen. At one point when
rotating the loop I could hear the signal too.
- The next test was to go out of the village on a different road (towards
Cambridge) to a car park adjacent to the Devils Dyke. This was 1.4km
away from the TX but about 40 degrees further to the west than the earlier
test locations. Immediately the loop was set up (leaning against the back of
the car) a good clear signal was visible, again no audible signal though.
- At this point I decided to "go for broke" and drove down another rural
lane to a roadside spot 3.6km away from home, but in the direction of
fire of the TX earth electrode loop. Setting up beside the country lane I
could see the QRSS signal on the screen!! Best orientation was with the loop
orthogonal to the village, which by now was too far away to see over the
slightly rising ground.
At this point my laptop batteries were dying
and I had to get some food for my wife for tea, so I packed up and came home,
very happy.
CONCLUSIONS
- Going from 10wpm CW to QRSS3 has made an amazing difference: signals
that cannot be heard are visible, and at decent distances. This is a new
experience for me, but not others here.
- The free running sidetone oscillator in the K1EL keyer is fine for
QRSS3, certainly for tests of about 1-2 hours long.
- I suspect some "utility coupling" is going on, although at the
furtherest point loop orientation did line up with the village. Is the
signal propagating along the water pipes to some extent?
- With "utility coupling" I suspect that getting a report from G6ALB in
the next village will already be possible on VLF as I've already heard my
signal at a greater distance than he is from me.
- At VLF, I am wondering just how far is possible in semi-rural areas with
manageable 50Hz noise levels (it is well filtered in my RX) and with some
degree of "utility coupling" which is inevitable in today's world where
pipes and wires criss-cross everywhere.
- Even with just 4W and QRSS, remarkable distances can be achieved.
Clearly I could get further than 3.6km already with the same equipment at
each end.
NEXT STEPS
- I need a location right out in the wilds (a bit hard to find in SE
England) for further tests, to see what performance is like without any
coupling into water pipes etc..
- Add the screen shots and audio clips to the sub-9kHz
webpage.
- Increase the area of the TX loop part that is in the air as this could
add another 3dB to signal level.
- More power? Loops at both ends? ....?
73s
Roger
G3XBM
--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM GQRP
1678 ISWL G11088
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