This year's "Alexanderson Day" transmissions will be Sunday, July 4, at 0900 and 1200 UTC. Transmitter tune-up will start a half hour sooner.
As always, the frequency is 17.2 kHz (not MHz), in CW, from Grimeton Radio in Sweden, callsign SAQ.
The transmitter is a vintage Alexanderson RF alternator. This is a type of AC generator once used around the world to replace "King Spark" right before vacuum tubes replaced everything. The 200 kW or so go to a truly majestic wire antenna on huge towers. The signal is audible worldwide with the right equipment (though that is saying a lot).
A WebSDR receiver that successfully receives other European signals (mostly military) in this low range is at: http://websdr.pa3weg.nl/. Its location gives an excellent chance of hearing SAQ.
The full announcement, with QSL information, is here.