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Date: Sat, 9 Apr 2011 21:31:40 +0100
Message-ID: <BANLkTikcZJMA+N8mOzurubDVS83VRDNaqg@mail.gmail.com>
From: Roger Lapthorn <rogerlapthorn@gmail.com>
To: rsgb_lf_group@blacksheep.org
DomainKey-Status: good (testing) 
Subject: LF: Another UK earth mode station
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>From the Sub 9kHz Yahoo group <http://tech.groups.yahoo.com/group/sub9khz/>.
M0DTS has started experimenting with earth mode conduction. Note that this
is NOT utilities assisted.

As it was superb weather today i decided to put some work into the tx system
> here.
>
> It consists of two tubes 1" round and 1m long in teh ground, the spacing
> was a convenient length in the paddock here at 17m.
> 75 ohm satellite coax (normally used for other uWave tests!) feeds
> across the two earth tubes.
> I connected my vna across the end of the coax in the shack and measured
> impedance of 94ohm at 9KHz.. not too bad.
>
> A spare TDA2002 was put into service for the simple audio amp (seen this
> before?!) and an audio transformer ( found in an old motorolla PMR
> speaker) was used to step up the output of the amplifier to the earth
> 'antenna'.
> It was not ideal as the output impedance of this transformer was
> measured at about 280ohm with a 4ohm resistor on the low impedance end.
>
> My pc was used to drive the audio amp at 8900Hz with on/off keying to
> ~1W of power into the 94ohm load (about 11v rms)
>
> The transmitter was not connected to any internal house metalwork, only
> the two earth rods outside.
> If i do connect to the house earth end i get trouble with my switch-mode
> psu shutting down!
>
> I received the beeper at 1.1km away in 50hz bandwidth using
> spectrum-lab's down converter to 600Hz, it was quite audible, tests at
> 2km showed no signal but i did not try lowering the bandwidth of the
> waterfall to try and identify it.
>
> The receiving end was the 1m multi turn loop with M0BMU preamp, this was
> tried facing the TX location and nothing heard, as i had read somewhere
> before the loop had to be flat on the ground to hear anything so it
> seems that there was no radiated signal.
> Getting the loop closer to the ground through the undergrowth made a
> large improvement.
>
> More tests to follow soon!
>
> Very interesting this low frequency stuff...
>
> Rob
> M0DTS
>

There have also been some interesting earth mode tests by LA3EQ recently.
Although the real long distance DX comes from those prepared to put the
effort into getting a signal radiated, earth mode is a fascinating mode and
able to be enjoyed by anyone with simple equipment.

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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>From the <a href=3D"http://tech.groups.yahoo.com/group/sub9khz/">Sub 9kHz=
 Yahoo group</a>. M0DTS has started experimenting with earth mode conducti=
on. Note that this is NOT utilities assisted.<br><br><blockquote style=3D"=
margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padd=
ing-left: 1ex;" class=3D"gmail_quote">
<div style=3D"margin-left: 40px;">As it was superb weather today i decided=
 to put some work into the tx system here.<br><br>
It consists of two tubes 1&quot; round and 1m long in teh ground, the spac=
ing <br>
was a convenient length in the paddock here at 17m.<br>
75 ohm satellite coax (normally used for other uWave tests!) feeds <br>
across the two earth tubes.<br>
I connected my vna across the end of the coax in the shack and measured <b=
r>
impedance of 94ohm at 9KHz.. not too bad.<br><br>
A spare TDA2002 was put into service for the simple audio amp (seen this=
 <br>
before?!) and an audio transformer ( found in an old motorolla PMR <br>
speaker) was used to step up the output of the amplifier to the earth <br>
&#39;antenna&#39;.<br>
It was not ideal as the output impedance of this transformer was <br>
measured at about 280ohm with a 4ohm resistor on the low impedance end.<br=
><br>
My pc was used to drive the audio amp at 8900Hz with on/off keying to <br>
~1W of  power into the 94ohm load (about 11v rms)<br><br>
The transmitter was not connected to any internal house metalwork, only <b=
r>
the two earth rods outside.<br>
If i do connect to the house earth end i get trouble with my switch-mode=
 <br>
psu shutting down!<br><br>
I received the beeper at 1.1km away in 50hz bandwidth using <br>
spectrum-lab&#39;s down converter to 600Hz, it was quite audible, tests at=
 <br>
2km showed no signal but i did not try lowering the bandwidth of the <br>
waterfall to try and identify it.<br><br>
The receiving end was the 1m multi turn loop with M0BMU preamp, this was=
 <br>
tried facing the TX location and nothing heard, as i had read somewhere <b=
r>
before the loop had to be flat on the ground to hear anything so it <br>
seems that there was no radiated signal.<br>
Getting the loop closer to the ground through the undergrowth made a <br>
large improvement.<br><br>
More tests to follow soon!<br><br>
Very interesting this low frequency stuff...<br><br>
Rob<br>
M0DTS<br clear=3D"all"></div></blockquote>








<br>There have also been some interesting earth mode tests by LA3EQ recent=
ly. Although the real long distance DX comes from those prepared to put th=
e effort into getting a signal radiated, earth mode is a fascinating mode=
 and able to be enjoyed by anyone with simple equipment. <br>
<br>73s<br>Roger G3XBM<br><br>-- <br><a href=3D"http://g3xbm-qrp.blogspot.=
com/" target=3D"_blank">http://g3xbm-qrp.blogspot.com/</a><br><a href=3D"h=
ttp://www.g3xbm.co.uk" target=3D"_blank">http://www.g3xbm.co.uk</a><br><a=
 href=3D"http://www.youtube.com/user/g3xbm" target=3D"_blank">http://www.y=
outube.com/user/g3xbm</a><br>
<a href=3D"https://sites.google.com/site/sub9khz/" target=3D"_blank">https=
://sites.google.com/site/sub9khz/</a><br><br>

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