Hi Roger!
 
Congratulations to your interesting achievements!
 
I have some questions: What was the antenna current you achieved @ 4 watts on 
0,8 kHz? Will you repeat the experiment on 8,97 kHz? It would be interesting if 
the signal at a given distance/location is stronger or weaker on 0,8 or 8,97 
kHz. Maybe you can create a diagram of the antenna impedance as a function of 
the frequency? This could give you further infos about you ground loop.
Could you use a saw tooth modulator (with a constant output voltage) that 
FM-modulates from DC to 9 kHz with a very slow rise time of say 1 minute? Thean 
you could evaluate the propagation as a function of the frequency (since your 
antenna is non resonant, so very broad band)! This would be most interesting!
 
I will also go on with my tests, reaching the far field on the Dreamers Band, 
there on the hill, without any water pipes or so. I have prepared many small 
and two big earth rods (steel, 1,5m long and a 2kg hammer ;-) ). Additionally i 
have organised further 280m wire... All very interesting stuff and an excellent 
hobby for the summer! :-)
 
GL and go on! Most of us haven't thought that this would work so good over such 
distances. Seems the radio amateurs are re-discovering the VLF band, just like 
at the beginning of radio...
 
73, Stefan/DK7FC
 
 
 

________________________________

Von: [email protected] im Auftrag von Roger Lapthorn
Gesendet: Mo 21.06.2010 18:55
An: [email protected]
Cc: M0BXT
Betreff: 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 <http://sites.google.com/site/g3xbmqrp/Home/earthmode>  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 
<http://sites.google.com/site/g3xbmqrp/Home/earthmode> . 
*   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.g3xbm.co.uk/> 
http://www.youtube.com/user/g3xbm
G3XBM    GQRP 1678      ISWL G11088

<<winmail.dat>>