Set 10        Receiver with loop antenna

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This receiver has a 26x38 cm loop antenna, made of 660x0.04 mm litzwire.
The loop antenna has 16 windings, and is wound around a frame made of wooden sticks.

Circuit diagram: Set 10

The transformers (type: 952.431) are with the 16 Ω output windings parallel connected, this gives an impedance of 8 Ω.
The connected headphone however gives a load which is twice as high (16 Ω).
This will make the input impedance of the transformers (normally 80 kΩ) almost double.
The total input impedance of the two transformers will now be about 300 kΩ.

As loudspeaker, a modern headphone is used (Sennheiser model: HD202).

With this receiver I took part in the Elmar memorial crystal radio dx contest 2006, and received 4 stations:
See the Contestlog Elmer 2006.xls

During the Dutch BTTF crystal receiver contest (december 2005) I received 6 stations with this receiver.
See the Contestlog BTTF 2005.xls

However, the number of received stations was quite low.

I measured the Q factor of the complete receiver, which was quite low (see measurement 1).
To find out the reason, first the diode was disconnected, this increased the Q quite a lot (measurement 2).
Then the two transformers were removed (measurement 3), because they were at close distance to the coil, there was influence on Q factor.

The next measurements are done with 1.4 Volt peak-peak across the LC circuit

Then  I connected 3 schottky diodes (5082-2835) in parallel to the receiver (measurement 4).
In measurement 4, a load resistor of 1.5 MΩ is used, because this is about the impedance of my transformer unit1.
 

Set 10 version 2

Then I replaced the 1.5 MΩ resistor (measurement 4) by the transformer unit 1, and connected a driver unit to it.
Both sensitivity and selectivity of the receiver was now much better then first.
With this version of the receiver, I took part in 2006 in a contest, and received 24 stations.
See the Contestlog sprint 2006.xls

Circuit diagram of: set 10 version 2 At the output, transformer unit 1 is connected.

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