I have in mind a Camping trip, go stay in
a field near Roger and have a few contacts on WSPR and ROS. No need to take a radio,
just stick the soundcard In/Out to a couple of ground stakesJ
-----Original
Message-----
From:
[email protected] [mailto:[email protected]] On Behalf Of Graham
Sent: 22 June 2010 23:35
To: [email protected]
Subject: Re: LF: VLF QRP Earth
mode: 5.1km DX tonight but no such thing as a free lunch
Why not try ros mf-1
into the ground, that's based round 1 Khz ? no
need for a time locked pc ?
Sent: Tuesday, June 22, 2010 11:10 PM
Subject: LF: VLF QRP Earth mode: 5.1km DX
tonight but no such thing as a free lunch
Second try at this post (without picture
that may have been too large)......
Further tests today to work out how far a signal on 838Hz will propagate
through the ground or air and how this happens. First thing
I tried was to go along the same country lane to the south of the village as
last evening at a distance of 4.2km (0.6km further than last night). Nothing,
zero, ziltch, and disappointment.
So, I then returned to the very same spot as last night (3.6km) and sure enough
the QRSS3 signal was clearly visible on the Spectran display. This was with the
loop pointing home across the fields. Then the crunch point: I put the loop on the ground flat on the road and the
signal went up. So, this was pretty conclusive proof that the signal was being
aided by pipework in the road. To check this, I moved 50m into a field and away
from the road and tried listening/looking for the QRSS3 signal with the loop
both flat on the ground and facing home - nothing at all. This was conclusive
proof that, at this distance at least, conduction through pipes was helping the
signal reach this far.
Next test was to go to a different roadside location some 4km west of the QTH
and try the same test again. Nothing copied at all, either with the loop
vertical or horizontally on the ground. I repeated the same test on the way
back towards home about 0.5km west of G6ALB's QTH, but again nothing seen.
Before coming home, slightly disappointed, I ventured up along a fenland road
where the soil is really dark peat. To my surprise, the signal was copied again
at good strength on the roadside 4.1km
west of the QTH with the loop facing the QTH. Again, I repeated the earlier test
and placed the loop horizontally on the ground. The signal was SO strong that
the Spectran trace turned red and I could clearly hear the QRSS3 signal by
ear!
A drive up a road called Lord's Ground Drove resulted in the signal still being
copied well just beyond Lord's Ground Farm at a distance of 5.1km. At this point I phoned my wife at
home and asked her to switch the TX over to 10wpm CW and the signal was
recorded with Spectran and clearly audible with the narrow filters in. Using
the crystal earpiece instead of the PC I was not able to hear the CW in the
50Hz noise. Listen to this recording at 5.1km from the TX but use
narrow filters around 838Hz to hear the 10wpm beacon signal clearly.
CONCLUSIONS
1.
At local distances (up to 0.5km) the signal
propagates by both conduction through the ground (aided by pipes in the ground)
and by induction (proved by the orientation of the loop when well away from
roads and pipes)..
2.
At greater distances (3-5kms) the signal reaches
its destination by conduction through the ground aided by pipes in the roads
and with inductive coupling into the loop at the RX.
3.
There is no evidence of induction playing a real
(long distance) part in propagation at 5.1km distance.
4.
When the signal is being "utility
coupled" the direction with respect to the TX earth electrode pair (and
loop formed in the ground) is not important. What matters more is whether there
are metal pipes between the TX and RX locations; if these are not present then
the signal will not be received, I think, at any great distance. There is some
possibility that coupling may also be possible as a result of overhead cables,
but this has not been tested.
5.
Even allowing for the conduction aided by pipes, I
am amazed that just a 4W TX into a 20m baseline earth electrode pair can be
copied so well at 5.1km (and probably considerably further), and even more
surprised that 10wpm CW copy was possible at this range.
6.
"Utility coupling" aided VLF earth mode
communications could be very viable over a range of at least 5kms.
FURTHER
WORK
1.
Try an E-field probe at 5km and greater distance.
It should reject 50Hz noise more and may work as well as the loop?
2.
Try to establish the limit of true induction
communications unaided by ground conduction paths.
3.
Sea coast earth mode test with one electrode in the
water and the other at the TX end, say, 100m inland from the water's edge. Just
how far would you be able to receive the signal along the coast using another
electrode pair or an induction loop?
So,
some useful further tests, but some disappointment. "There is no such
thing as a free lunch", as they say. For real VLF work Stefan's true
radiation experiments are where the action REALLY is.
All good fun and I've learnt a lot. There's a screen shot of the received QRSS3
signal (strong!) plus the recording of the 10wpm CW signal at 5.1kms on my earth
mode website .
73s
Roger G3XBM
--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM GQRP 1678 ISWL G11088
