Searching Local QRM

The following sonagrams and FFTs will help you to find local intruders:‎

Plasma-TV from Loewe (German product!) – shortwave killer – sonagram: 3500 kHz ‎‎– receiver set to USB – producing QRM from 0.1 – 28 MHz‎

click to hear the sound

Plasma-TV from Loewe – German product - shortwave killer – ‎
sonagram and FFT: 3500 kHz – AM - producing QRM from 0.1 – 28 MHz‎

Click to hear the sound 

Plasma-TV  shortwave killer – sonagram on  3515 kHz – USB ‎

Click to hear the sound

‎ harmonic radiations on all bands

Click to hear the sound



TV – switching power supply
accumulations in 30 kHz increments, 50 or 100 Hz spectral lines‎

Click to hear the sound


Radiation of a computer monitor, switching power supply

Click to hear the sound


Radiation of a TFT- computer monitor‎
very weak (9 dB over white noise), but audible – ‎
spectral lines in 50 kHz increments

Click to hear the sound

Radiation of a broadband DSL-Modem on 10, 21 and 24 MHz‎
‎-‎ very unstable signal – radiation source: DC power supply cable -‎

Click to hear the sound

DC PS black cable with filter (white) – 30 dB reduction of the disturbing ‎signal!‎

Radiation of a brandnew combined fax-telephone ‎
device (made in Thailand) ‎
Spectrogram with Perseus - showing the interference from 10 kHz – 30 MHz!‎

Clcik to hear the sound


‎             0                    5                    10                   15                   20                   25                    30   MHz‎

The same device -  spectral lines with 50 kHz and 400 kHz increments – ‎here: on 10 MHz ‎

Click to hear the sound

PLC – shortwave killer in Portugal
producing QRM from 1  - 30 MHz – reported by CT4AN‎

Click to hear the sound

You can get similar sonagrams with all soundcardprograms, which are displaying a “waterfall” !!!‎

For example: Gram50, Spectran, Multipsk and others. Spectrograms are not very helpful in such ‎cases. Waterfall = sonagram. Additional sound files are available here for comparaison purposes

Screenshots: DK2OM with Wavecom W61 and Perseus‎                                                 

credits: ‎
Wavecom Elektronik – Buelach –Switzerland
SSB-Electronic – Iserlohn – Germany‎
Compiled and published by DK2OM

Published April 2009