RTL 234 kHz power, April 2018Pieter-Tjerk de Boer, PA3FWM firstname.lastname@example.org
Below is a plot of the signal strength of RTL's 234 kHz longwave transmitter as
received in Enschede, the Netherlands over the month of April 2018.
Vertical axis is relative power in dB; carrier power has been averaged over
1-second intervals and plotted as dots. Horizontal axis is UTC time.
At night, the signal strength is highly variable: fading due to skywave and groundwave.
At daytime, there's only the groundwave. The remaining fluctuation must be due to the transmitter power varying. We see that it varies quickly by about 4 dB, presumably due to dynamic carrier control techniques. But more surprisingly, we see that it is 1.8 dB lower on weekends!
Many LW/MW radio stations change their power in a diurnal pattern, typically reducing power at night when propagation is more favourable due to the skywave. But for a weekly pattern, the reason can only be commercial; perhaps fewer listeners in the weekend?
In fact, if we zoom in a bit, we see that RTL also has a daily power reduction:
every weekday evening at 18:00 UTC, 20:00 local time, power is also reduced by 1.8 dB,
just before the skywave influence starts:
We can't see at what time next morning the power is increased again, since that happens during the skywave period.
Presumably, all of this is done to save energy and thus expenses. Nominally, the RTL transmitter runs at 1500 kW, according to MWLIST. Subtracting 1.8 dB from that gives 1000 kW.
Looking back at earlier data, the weekend power reduction has been going on since at least November 2017. It is only tied to weekends, not to other holiday days, like May 1st (last day in the above plots) or the days around Christmas and New Year.