Message-ID: <4C099741.90808@iup.uni-heidelberg.de>
Date: Sat, 05 Jun 2010 02:16:01 +0200
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3
MIME-Version: 1.0
To: rsgb_lf_group@blacksheep.org
References: <001401cb02f4$4aa9d130$0401a8c0@xphd97xgq27nyf>	<00b701cb030b$c6268d50$0201a8c0@Clemens04>	<01CA4D0605FB409ABD7D2F0A98DC46BD@df2py>	<4C08002C.5070500@iup.uni-heidelberg.de>	<4C09114F.5090605@iup.uni-heidelberg.de> <AANLkTimyVeB_56ycD4DhU9wTP8z72HovaRusP4_LEapW@mail.gmail.com>
In-Reply-To: <AANLkTimyVeB_56ycD4DhU9wTP8z72HovaRusP4_LEapW@mail.gmail.com>
Subject: Re: VLF: 2km on 8,97 kHz using 6W TX power and a 120m earth antenna
Content-Type: multipart/alternative;
 boundary="------------020205080107030005010400"
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


--------------020205080107030005010400
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

Hello Roger,

Am 04.06.2010 21:48, schrieb Roger Lapthorn:
> Stefan,
>
> A few observations on your tests using the earth electrode "antenna" 
> today:
>
>    1. In my experience, most of the signal transmission is by
>       induction, so I think it would be worth trying to receive the
>       signal with a loop antenna when the received signal may be much
>       stronger than on the E-field probe. In my case I use a 30turn,
>       80cm square, loop which can be rotated to minimise 50Hz
>       interference.
>
Yes, a loop would be a better RX antenna when transmitting with such a 
earth antenna, at least in the near field. But i do not have a loop RX 
antenna and my goal was to compare by both grabbers that use E field 
antennas. It is important to have a signal within the dreamers band to 
compare the grabber setups. Here, a weak signal may be even an advantage 
since it is easier to compare the S/N (readability) of those 2 systems. 
If i want to produce a strong signal i think i prefer the kite ;-)
>
>    1. On my 10m and 20m baseline earth electrodes I was measuring
>       resistance of between 40-60 ohms between 1-9kHz, so your figure
>       seems very high. This may be as a result of the soil and rock
>       type in your area but this is worth checking. If my theory of
>       the "loop in the ground" is correct then a poor conductivity
>       soil would result in a larger effective loop area within the ground.
>
This hill is very stony and so the losses are high as well. I had 
problems to push those earth rods into the earth. They stopped in about 
30...40 cm. I had just 2 of them. In the next test i will take 2x3 
copper earth rods (already prepared). Probably my next near field test 
will be in 3,2km and i will use a 800m wire antenna, also on a hill.
>
>    1. Did you try matching the PA to this high impedance through a
>       transformer? I think not in this test, so better results may
>       well be possible.
>
My PA has an output transformer where you can get 12V,24V,36V,48V and 
96V (about, depending on the battery voltage, of course). These 96V were 
not enough. So i just have to add another winding for 96V and switch it 
in series to get a 6dB stronger signal or i use a second ferrite core 
transformer for e.g. 400V output (no problem). Additionally the earth 
losses will be reduced. But my main interest will be the kite antennas ;-)
Maybe i will do a test with Bernd/DF8ZR in 16km, using a 800m antenna 
and 600W. This can be done with rain and without wind ;-) But it depends 
on Bernd's interest...

73, Stefan/DK7FC

--------------020205080107030005010400
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
  <meta content="text/html; charset=ISO-8859-1"   http-equiv="Content-Type">
</head>
<body bgcolor="#ffffff" text="#000000">
Hello Roger,<br>
<br>
Am 04.06.2010 21:48, schrieb Roger Lapthorn:
<blockquote   cite="mid:AANLkTimyVeB_56ycD4DhU9wTP8z72HovaRusP4_LEapW@mail.gmail.com"   type="cite">Stefan, <br>
  <br>
A few observations on your tests using the earth electrode "antenna"
today:<br>
  <ol>
    <li>In my experience, most of the signal transmission is by
induction, so I think it would be worth trying to receive the signal
with a loop antenna when the received signal may be much stronger than
on the E-field probe. In my case I use a 30turn, 80cm square, loop
which can be rotated to minimise 50Hz interference.<br>
    </li>
  </ol>
</blockquote>
Yes, a loop would be a better RX antenna when transmitting with such a
earth antenna, at least in the near field. But i do not have a loop RX
antenna and my goal was to compare by both grabbers that use E field
antennas. It is important to have a signal within the dreamers band to
compare the grabber setups. Here, a weak signal may be even an
advantage since it is easier to compare the S/N (readability) of those
2 systems. If i want to produce a strong signal i think i prefer the
kite ;-)<br>
<blockquote   cite="mid:AANLkTimyVeB_56ycD4DhU9wTP8z72HovaRusP4_LEapW@mail.gmail.com"   type="cite">
  <ol>
    <li>On my 10m and 20m baseline earth electrodes I was measuring
resistance of between 40-60 ohms between 1-9kHz, so your figure seems
very high. This may be as a result of the soil and rock type in your
area but this is worth checking. If my theory of the "loop in the
ground" is correct then a poor conductivity soil would result in a
larger effective loop area within the ground.<br>
    </li>
  </ol>
</blockquote>
This hill is very stony and so the losses are high as well. I had
problems to push those earth rods into the earth. They stopped in about
30...40 cm. I had just 2 of them. In the next test i will take 2x3
copper earth rods (already prepared). Probably my next near field test
will be in 3,2km and i will use a 800m wire antenna, also on a hill.
<blockquote   cite="mid:AANLkTimyVeB_56ycD4DhU9wTP8z72HovaRusP4_LEapW@mail.gmail.com"   type="cite">
  <ol>
    <li>Did you try matching the PA to this high impedance through a
transformer? I think not in this test, so better results may well be
possible.</li>
  </ol>
</blockquote>
My PA has an output transformer where you can get 12V,24V,36V,48V and
96V (about, depending on the battery voltage, of course). These 96V
were not enough. So i just have to add another winding for 96V and
switch it in series to get a 6dB stronger signal or i use a second
ferrite core transformer for e.g. 400V output (no problem).
Additionally the earth losses will be reduced. But my main interest
will be the kite antennas ;-)<br>
Maybe i will do a test with Bernd/DF8ZR in 16km, using a 800m antenna
and 600W. This can be done with rain and without wind ;-) But it
depends on Bernd's interest...<br>
<br>
73, Stefan/DK7FC<br>
</body>
</html>

--------------020205080107030005010400--