Stefan,
if I remember well the antenna voltage of an unloaded and untuned small loop
antenna is proportional to the loop area (all : please correct if I am wrong).
So, as Marcus suggested you could measure the induced voltage in a loop with a
known area and based on the voltage ratio (earth antenna versus reference loop)
you could calculate the effective area of you earth antenna.
73, Rik ON7YD
________________________________________
Van: [email protected] [[email protected]]
namens Stefan Schäfer [[email protected]]
Verzonden: woensdag 14 juli 2010 14:02
Aan: [email protected]
Onderwerp: Re: LF: RE: DLF passive received with earth antenna
Hello Rik, VLF,
Yesterday i have measured the receiving voltage of DHO38 on my earth
antenna. I used an impedance converter with an OP AMP, so the input
impedance can be seen as infinity. I got a signal level of -20 dB.
Markus/DF6NM calculated/measured that i have to add 11 dB when comparing
the broader MSK signal to a narrow reference level of my VFO (I set
SpecLab to a 3 Hz FFT when recording the DHO level). My VFO causes a
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
kHz. The distance between TX and RX is 411 km and the angle between TX
and the antenna optimum is 3 deg (so one has to add a factor 0,998 =>
negligible). The problem is that i do not know the ERP but maybe one can
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
antenna with a known area A. I will do this in some days. Maybe it is a
more accurat measurement since propagation effects are compensated that way.
Rik (or others), how would you estimate the effective antenna area of
the loop for that frequency with the given parameters?
Sadly the earth antenna is orientated to Markus with its minimum, so i
cannot do any test with Markus' RX. BUT, Michael Oexner, one of those
who have received my signal of the kite antenna, is in a distance of
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
configuration i want to try to reach a new record in "earth mode DX",
currently 10km as written in Roger's list.
An important information is achieved when estimating / calculating the
effective antenna area: One can see if an increase of the wire length (
or better said: the distance between the ground electrodes) results in
an improvement of this area with the power 2. When doubling the distance
between the electrodes results only in a liear improvement of the loop
area, the soil conductivity seems to be higher below the added wire. So
it would make more sense to add another wire on the other electrode, on
the top of the mountain. Then, the antenna can be used as a "short"
dipole as well. Maybe for 137 kHz.
All this is a really interesting field. I think not only for VLF but
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 correct
> load you would be able to calculate the efficiency of the antenna (knowing
> distance to and ERP of DLF)
>
> 73, Rik ON7YD
>
> ________________________________________
> Van: [email protected] [[email protected]]
> namens Stefan Schäfer [[email protected]]
> Verzonden: vrijdag 9 juli 2010 0:26
> Aan: [email protected]
> 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
>
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