The RF-Spectrum during 24 hours

This study was performed to get an overview about the variability of the rf-spectrum during 24 hours. Monitoring was done from 19.03.2012, 17:40 to 20.03.2012, 17:10 at the location of Algermissen, northern Germany (52° 15’ 9’’ N 9° 58’ 43’’ E).Time is given as local time. Antenna is the DX500 manufactured by RF-Systems. For solar activity see table 1 (taken from


Solar sun spot number (NOAA)

Solar flux (NOAA)

Planetary K-indices









The rf-spectrum from 100 Hz to 12.500 kHz was scanned with a resolution of 10 kHz and a cycle rate of 1 h using the feature “Monitor” > “Observe frequency band” of the AR5000RA program. So each frequency is represented by 24 samples of agc over 24 hours. Because of strong interference by man made noise the scans at 19:40 and 20:40 hours had to be sorted out. To get a first idea of the diurnal variability of the rf-spectrum for each scan the standard deviation of all agc-data of a scan is calculated and plotted here

Plot: Standard deviation per frequency and 24 hours

The scan started at 18:40 hours displays highest variability and the scan started at 13:40 hours shows the lowest variability. The rf-spectra of these two scans are plotted below:

Plot: rf-spectra from 18:40 hours and 13:40 hours

The main differences between the two scans can be found within the broadcast bands (indicated by grey bars) with exception of the tropical bands. Outside the broadcast bands differences can be noted around 4000 and 6800 kHz.

Based on these findings 8 frequency-sections are selected for further investigation by means of a radar plot. In this type of plot a centered circle indicates no diurnal variance. For each of the 8 frequency sections per scan the mean of the agc-data is calculated. These means are plotted against the circular time axis:

Radarplot: radiosignals plotted against a circular time axis

The blue shaded area of the graph indicates night time. Following the diurnal conditions of the ionosphere the MF band (0.6 - 1.6 MHz, black) shows during night time much higher signal-levels than during daytime. Almost the opposite is true for the 25m band (11.6 - 12.3 MHz, brown). The signals of the 31m band (9.2 - 10 MHz, yellow) seem to behave rather indifferent with respect to night or day. However main activity concentrates between 17 and 22 hours local time. Most listeners can be expected during this period of time. This maximum of activity can also be observed for the 49m band (5.9 - 6.9 MHz, violet) and the 41 m band (7.2 - 7.6 MHz, orange) but with enhanced signal levels during night time.