Whistle point

One speaks of a whistle point when interfering and undesired signals are apparently received in a radio receiver that do not come from the antenna, but rather come from the demodulator of the receiver itself.

When turning the frequency scale of a single sideband receiver , unmodulated signals can be heard as whistling tones. The pitch results from the difference between the set frequency and the frequency of the signal.

When cranking, a high-pitched tone can first be heard, the frequency becoming lower and lower until the set and received frequencies are the same. If you continue to turn in the same direction, the pitch rises again.

Since every receiver (apart from very simple architectures) contains oscillators , the harmonics of these oscillators can fall into the reception range and thus cause whistling. If there are several oscillators, mixed products can also create the whistling points. Modern receivers with microprocessor control always generate a series of undesirable high-frequency signals through the clocks of the processor, display, keyboard scanner, etc., which appear as whistling points if there is insufficient shielding.

literature

• R. Rudersdorfer, with the collaboration of U. Graf and H. Zahnd: Funkempfangerkompendium. 1st edition, Elektor-Verlag, Aachen 2010, ISBN 978-3-89576-224-6 .