Item nr.

Gerard TelRaam Loop antenna

Directional and tuned antenna.

Data for Gerard TelRaam
ProductionThe Netherlands, 2003.
BandsMW (522-2000kHz).
CabinetWood. Size (height) 124cm.

The Design

Following a design of Dave Schmarder, this antenna, built as a crystal set has a quite big open loop coil. In this way, the coil itself operates as an antenna and this allows the set to be used without an outdoor antenna or ground. After construction, in Zeist we receive Arrow (675kHz, 120kW, 15km) and 747AM (747kHz, 400kW, 60km) using the coil only. Arrows comes in strongest and generates about 50mV of DC over the resistor following the detector. These stations have now since long ceased operation.

You can see the crystal receiver circuitry on this photo, but later I have removed it, because I use this construction mainly as a MW antenna for active receivers.

You can calculate the construction of Loop Antenna's approximately with my Excel sheet LoopAnt; see the TelRaam Calculation.

Obtained9/2003 from home made.
Sound samplePLAY SOUND   It was intended for MW, but because the capacitor has no padding cap, its capacity can go quite low so the upper frequency limit is around 2000kHz. Connected to my Philips D2999 (with a toilet roll on the capacitor to reduce hand effect during tuning), I received amateur stations on the 160m band. If I understand Rudy well, he operates a square antenna with quarter wavelength sides near Hamburg, at a height of 16m above the ground. Call DK3XY reports Karwitz so in der nähe means 80km away, recorded at about 403km from Karwitz.

This Object

It was a construction project with my daughter (10y). It took us one evening to build the wood structure (including the drilling of holes), one evening to spin in all the wires for the coil, one evening to collect and mount electrical parts, and one evening to solder and finish. (In one evening we work for about an hour, then it is bed time.)

Dave writes on his page that one needs good ears, but a larger coil improves performance. So we made the coil a little bit bigger than Dave's: the width of the coil is 80cm and it has 13 turns. The 13 turns with variable capacitor form the resonance circuit, the coil is tapped 6 turns from the ground to connect the diode (1N34A).

An outdoor antenna can be coupled through a 2-turn coupling coil. But coupling also works the other way: through the coupling coil, you can feed the HF energy to another receiver. The set then works as a tuned, directional, magnetic coil antenna, which may improve your MW reception dramatically. When tuning, especially in the higher MW regions, you will observe a considerable hand effect: touching the metal tuning knob will change the frequency, so if you tune to max signal and lose your hand from the knob, signal gets worse. To remedy this, I attached a large plastic disc to the tuning condenser. It size allows very exact tuning.

I recommend everybody who has a 10-year daughter to build this set. It is fun!

Part of Gerard's Radio Corner.
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