Where do I find pirate or hobby radio stations on Short or medium wave?
Some bigger shortwave stations broadcast for 24 hours, or even over a whole weekend, maybe once a month. Other stations broadcast on an irregular basis; basically when they can and usually for a short time only, maybe an hour or so, or even less.
Medium Wave: Stations, mostly from the Netherlands or Greece are found at the top part of the band, between 1602 and 1700 kHz. Many portable radios only cover up to 1620 kHz, so you will need a radio capable of receiving these frequencies. The band can get quite busy in and just before the hours of darkness.
48 metres: Stations are usually found in the segment between 6200 and 6400 kHz, but are sometimes found above or below those frequencies. Frequencies around 5800 are being used more often recently. AM is mostly used, although low power stations may use SSB to cover greater distances, at the expense of sound quality. This band and 43 metres work best in the hour before darkness, and an hour or two after sunset. In summer the band can stay open for short and medium skip all night. In the middle of winter short and medium skip tends to stop quite soon after dark, and only longer distances are possible, e.g. 800 km or more.
43 metres: A few European stations use the segment above 6800 up to 6995 kHz. This is the part of the band where North American pirates mostly operate. Listen for US pirates late in the winter evenings. Some stations may be found below these frequencies (above is the 7.0 - 7.2 MHz amateur band).
Other bands: Some stations operate in or just above or below the short wave broadcast bands. Around 3905 or 3930 is often used in the 75 metre band , above 7500 kHz is sometimes used (41 metres), and other frequencies on the edges of the shortwave broadcast bands.
Studying the various web sites that log stations (like this one!) can give you a guide to where other stations might be in the future.