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Date: Wed, 14 Jul 2010 14:02:37 +0200
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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Subject: Re: LF: RE: DLF passive received with earth antenna
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Hello Rik, VLF,

Yesterday i have measured the receiving voltage of DHO38 on my earth=20
antenna. I used an impedance converter with an OP AMP, so the input=20
impedance can be seen as infinity. I got a signal level of -20 dB.=20
Markus/DF6NM calculated/measured that i have to add 11 dB when comparing=
=20
the broader MSK signal to a narrow reference level of my VFO (I set=20
SpecLab to a 3 Hz FFT when recording the DHO level). My VFO causes a=20
level of -9 dB in SpecLab when it (the VFO) is set to 44 mVp.

So, we have a single turn loop and measure a level of 44 mVp at 23,4=20
kHz. The distance between TX and RX is 411 km and the angle between TX=20
and the antenna optimum is 3 deg (so one has to add a factor 0,998 =3D>=20
negligible). The problem is that i do not know the ERP but maybe one can=
=20
normalize it to the ERP. Does anybody have an idea of the ERP of DHO38?

Markus meant i can make a reference measurement with a small loop=20
antenna with a known area A. I will do this in some days. Maybe it is a=20
more accurat measurement since propagation effects are compensated that wa=
y.

Rik (or others), how would you estimate the effective antenna area of=20
the loop for that frequency with the given parameters?

Sadly the earth antenna is orientated to Markus with its minimum, so i=20
cannot do any test with Markus' RX. BUT, Michael Oexner, one of those=20
who have received my signal of the kite antenna, is in a distance of=20
about 50 km. The angle is abt 35 deg ( so a factor of 0,8).
This week i will increase the antenna length to about 500m. With this=20
configuration i want to try to reach a new record in "earth mode DX",=20
currently 10km as written in Roger's list.

An important information is achieved when estimating / calculating the=20
effective antenna area: One can see if an increase of the wire length (=20
or better said: the distance between the ground electrodes) results in=20
an improvement of this area with the power 2. When doubling the distance=
=20
between the electrodes results only in a liear improvement of the loop=20
area, the soil conductivity seems to be higher below the added wire. So=20
it would make more sense to add another wire on the other electrode, on=20
the top of the mountain. Then, the antenna can be used as a "short"=20
dipole as well. Maybe for 137 kHz.

All this is a really interesting field. I think not only for VLF but=20
also for LF, if soil conductivity is low enough :-)


73s, Stefan/DK7FC



Am 09.07.2010 00:39, schrieb Rik Strobbe:
> Stefan,
>
> I you could measure the power delivered by the earth antenna to a correc=
t load you would be able to calculate the efficiency of the antenna (knowi=
ng distance to and ERP of DLF)
>
> 73, Rik  ON7YD
>
> ________________________________________
> Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.=
org] namens Stefan Sch=E4fer [schaefer@iup.uni-heidelberg.de]
> Verzonden: vrijdag 9 juli 2010 0:26
> Aan: rsgb_lf_group@blacksheep.org
> Onderwerp: LF: DLF passive received with earth antenna
>
> Roger, LF,
>
> Just forgotten to mention: Today i tried just for fun if it is possible
> to make the Deutschlandfunk DLF / 153 kHz audible in a car speaker (4
> Ohm) without any additional energy sources and using my 300m earth
> antenna that is fixed installed on the hill.
>
> It is possible! The level is not too loud but you clearly can understand
> all what they say when holding the speaker in a distance of 0,5m to the
> ear. I just used a bridge rectifier out of 4x BAT47 diodes and a 10nF C,
> that's all ;-)
>
> There was not really a difference when using a 1:4 audio transformer (4
> Ohm on low impedance side).
> Currently the R-loss of the earth antenna is 1 kOhm although it was 650
> Ohm in the last TX test. Probably this is due to the heat...
>
> Maybe it has to be mentioned that DLF transmitts 500 kW and is in a
> distance of 40 km to that QTH ;-)
>
> 73, Stefan
>   =20