Hello Roger,
Interesting tests. Since the near field is much wider on 1 kHz, you
should get some distance there if you arrange a big ground loop. Do you
plan some /p tests in the near forest beside your house? A simple
battery fed PA in the range of 10 W or below could show interesting
results.
I plan to re-activate my earth antenna as well. It was unused some
months now but spring is coming and i have a new PA to test ;-) Some
tests last year on 1970 Hz were negative due to the high local QRM.
Anyway i'll plan to try it again.
Good luck and fun with your tests.
73, Stefan/DK7FC
Am 12.04.2011 17:46, schrieb Roger Lapthorn:
When testing with utilities assisted earth mode in recent
months I seemed to be getting weaker signals at 8.76kHz compared with
my tests at 0.838Hz last summer. So, today I decided to go back and
recheck results at a lower frequency at test sites 1.6, 2.6, 4.5 and
5.1km away from the 5W QRSS3 transmitter at home. Test locations were
rural fenland roadsides, a National Trust car park and 2 roads in the
next villages.
I used the same TX as at 8.76kHz, but divided down by a further x8 to
1.095kHz using the 4060 divider. The receiver was a horizontally
orientated 30turn, 80cm across, series tuned loop into a low impedance
MPF102 FET preamp with a drain circuit peaked at around 1.1kHz and
emitter follower into PC running Spectran.
My initial test at 1.6km was a total failure - no signal visible at all
in Spectran at 0.73Hz bandwidth. Then I realised that I had BOTH the
garden earth electrodes in use at the TX (neither connected to pipes).
A phone call to my wife and one wire was connected to the pipework in
the house with the other still connected to the earth electrode at the
bottom of the garden some 20m from the house. The signal then appeared
at good strength.
Signals were received at all test locations indicated, but there was no
signal visible (in QRSS3 bandwidths at least) when moving away from the
roads into nearby fields or at some other test locations where pipes
were absent (or plastic). At one location I rested the loop within 2m
of one of the fenland water courses, but nothing was detected. The
image attached (visible on the LF-reflector only) is the signal at
4.5km, which is strong in 0.79Hz bandwidth. Even stronger signals are
possible with more optimum positioning, but I keep having to move my
loop to avoid it being crushed by oncoming farm tractors! I do get some
odd looks too.
My conclusions from the tests to day are:
- This was definitely utilities assisted earth mode. The initial
(accidental) test today with 2 earth electrodes not connected to water
pipes failed.
- Signals are strong close to where the metal pipes are, but
rapidly disappear where no (metal) pipes are close by.
- Signals at 1.095kHz are definitely stronger than at
8.76kHz in the 3-5km range.
There is one more test to do at some point that needs some assistance
locally (I think within 10km to work). I want to try a long stable
carrier test with someone looking in the very narrow bandwidths we've
been using for the radiated tests recently. What I'm wondering is just
how far from the pipes does an earth mode signal "leak"? Using Spectrum
Lab with the very weak signal bandwidths like 0.4-2mHz, the weak
remnants of a signal might just be visible some way from the "easy"
utilities assisted coverage area.
The remaining tests I want to do still with earth mode are:
- River bank or sea coast test - just how far can one get?
- True earth mode in open country without any utilities
assistance
- Earth mode at higher frequency e.g. around 70kHz, which I can
manage with my present set-up. Based on recent OFCOM correspondence I
believe such tests would be legal as long as there is no intentional
radiated signal or interference to others.
This class of experiment is not in the same league as those being done
by the radiating VLF DXers, but fun nonetheless, especially as anyone
can do this sort of test without NoV or special permits needed.
73s
Roger G3XBM
--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
https://sites.google.com/site/sub9khz/
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