Experiments with LC circuits part 11
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In this article some measurements on my
detector unit 1 .
Detector unit 1.
The received voltage across the LC circuit is measured when tuned to my local station "Groot Nieuws Radio" on 1008 kHz (100 kW 41 km distance).
In this test, the diode in the detector unit is disconnected.
No external antenna is connected, only the coil in the unit is used as a loop antenna, which is tuned with the tuning capacitor.
The following test setup was used:
The voltage across the LC circuit is measured with a high impedance amplifier (version 2), followed by this diode detector and a voltmeter.
The detector unit is turned in 20 ° steps in the horizontal plane, in every step the received voltage is measured.
By this means, the directional properties of the detector unit are measured.
This test is also done at different situations,
Measurement 91 - inside the house at 0.7 metre above ground, and at daytime.
Measurement 92 - outside the house at 0.7 metre above ground, and at daytime.
Measurement 93 - on the attic at 6.0 metre above ground, and at daytime.
Measurement 94 - inside the house at 0.7 metre above ground, late in the evening when the sun was down for hours.
A direction of 0° means, the back of the
receiver is facing the north, and the front is facing the south.
From my location, the transmitter is in the direction of 50°.
The measured voltages are the peak levels off the (un-modulated) carrier.
The next diagram shows the results of the measurements.
Received voltage at different coil orientations
As we see, the received voltage is maximum when the back or front of the detector unit is pointed towards the transmitter.
This is logical, because then the maximum of magnetic field lines go through the coil.
The difference in received voltage between inside and outside the house seems to be small.
Also there is hardly any difference between daytime and night-time values.
The received voltage on the attic is slightly higher, then on ground level.
On the attic, the directions of maximum received voltage seems to be 20° beside the transmitter direction.
Or the compass which I used to determine the direction had some error on the attic.
I have a lot of stings stored on the attic, maybe something magnetic was too close to the compass.
Later I thought, maybe the error in the compass reading was caused by the solar panels on my roof , under which I did the measurement on the attic.
The solar panels and connecting cables form a very large "one turn loop", with several Ampere DC current through it, producing a magnetic field.
But a later check showed there was only influence from the solar cables when they were within 20 cm from the compass.
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