Hi Stefan,
2011/10/12 Stefan Schäfer <[email protected]>:
> Reminds me on local LF experiments. But even on 8970 Hz i have 38 confirmed
> receptions, see http://dl.dropbox.com/u/19882028/VLF/VLF_11th_all.png
I have read your adventures in the "dreamer's band" and I admit it has
been very inspiring.
Yes, I am planning some VLF activity soon. I have already got a kW
capable audio amplifier, so all I will need is to measure the
impedance at 8.9 kc (or so) and figure out the matching and also to
get some people around the area to connect their soundcards to an
appropriate antenna! The latter will be a bigger challenge I suspect.
>> By the way, has anyone in the group experimented with transmitting
>> into the ground with earth probes?
>
> Yes, G3XBM, others and me. I have a 700m long "earth antenna". The electrode
> pairs are 600m distant. Average height above ground is about 6m (2...10m). I
> was received in 46 km distance at 8970 Hz in DFCW-600 (Michael Oexner) and
> about 450 km in QRSS-3 on 137.7 kHz (F5WK). G3KEV also reported about traces
> of my transmission on LF. He is 830km distant. I used 100W RF power.
Was the 450 km reception done during the day or night? At that
distance I am guessing the RX station is not receiving anything from
the earth, it will all be coming from above ground. I am curious if
this was pure ground wave or sky wave.
By the way, why did you elevate the wire off the ground? I am just
letting the (insulated) wire sit on the ground. I think that this
results in more energy transferred in the ground capacitively. Maybe I
should try elevating the wire to see what difference that makes.
> Well, on VLF it is a pure earth antenna but on LF it must be a mixture of
> that and a low short wire above ground.
> I haven't done excessive experiments on LF, like finding the radiation
> pattern and so. Maybe that would be interesting.
With the limited experiments I have done, I think there is some
directionality but it's hard to say if this is due to the geology of
the area or the direction of the earth dipole.
> If you have a region with plenty space, you must try a loong baverage to EU
> please :-) You could also use that for TXing whithout expecting too much of
> course, just for the fun. Can you arrange a 3 Lambda wire in VK? :-)
If it can't be done in VK, then it can't be done! I may need to travel
a bit further out, but I am very very sure this is possible here. Now,
where do I get 6.6 km of wire? :-)
> What are your plans and who is the next distant LF station to you? How many
> amateurs can radiate a 1 W ERP signal in VK, do you know?
I don't know of anybody that can radiate 1 W in VK. Not a lot of
amateurs per square km here and generaly not much activity on LF. I
think there may be a couple of well equipped amateurs in NZ but if
they are active, I am unaware of their schedules.
Anyway, I am having a good vibe about experimenting more with the
earth dipoles, so the next steps will be more wire, more power and
different configurations. I am feeling much more relaxed pumping more
power in the ground because it has such a nice and predictable purely
resistive impedance - no fiddly and dangerous inductors are needed,
just a good ol' impedance transformer.
So many things to try, so little time!
73, Dimitris VK1SV
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