The compact circuit presented here is perfect for receiving the signals from pulsed fixed frequency transmitters. Chest straps from several well-known brands (Polar, Huger, Kettler, Crane, Outbreaker, …) transmit a short signal burst with a frequency of 5.3 kHz. These signals can be received and used in your own projects, as the author shows on his website .
The circuit uses a ferrite rod with 1000 turns of 0.2 mm enameled copper wire and a (tuning) capacitor to receive the signals. The value of the capacitor (22 nF) has been selected for use at a frequency of about 5.3 kHz, but this can, of course, be adapted for use at different frequencies. The received signals are amplified by opamp (IC1), after which a NAND gate (IC2) turns them into a nice waveform with straight edges. For the supply you can use any DC voltage source in the range of 9 to 18 V. There is a board layout available , which can be ordered via ThePCBShop .
Web links http://www.elektor. com/080093  www.thepcbshop.com