The suggestion that there is a window for Radio Botswana reception on 4830 kHz from 0400 (when Radio Tachira signs off) to 0900 (when Radio Botswana signs off) is not totally correct. Tropical band reception is only possible with a darkness or near-darkness path. Long distance reception of a signal on 60 meters ceases to be possible shortly after sunrise at the transmitter site. According to my DX Edge screen, "Arnold" passes thru Botswana at around 0500 UTC at this time of year (i.e., July).
Tropical band reception from northern South America - stations like Radio Tachira 4830 - is pretty predictable. They're there almost all the time. Good conditions mean a better signal, but there's usually something there even under the worst conditions.
Tropical band reception from southern Africa (and eastern Africa) is a lot more dependent on the conditions. You might try several weeks and not hear a peep from Radio Botswana. Then one night when conditions to southern Africa are exceptionally good you may hear them mixing with or even on top of Radio Tachira BEFORE Tachira's 0400 sign off. Listen for their interval signal of cows mooing and chickens crowing. Also check their 90 meter frequency. I think it's 3355 kHz, but check the World Radio TV Handbook or Passport to World Band Radio to be sure.
Reception of all but the easiest tropical band stations requires regularly tuning the bands so that you are there when there's a good opening. Most of the stations are NOT normally received regardless of when the reception window is open. Only occasionally are conditions good enough to allow reception of these weak signals. But if you check frequently (especially from Sept to April), you may be amazed at how many stations you hear once or twice under good conditions.
If you want to know more about hearing stations in the tropical bands, join NASWA (The North American Shortwave Association; 45 Wildflower Road; Levittown, PA 19057). NASWA has the best coverage of any North American radio club of both tropical band and international shortwave broadcasting. Send $2 for a sample copy and see for yourself. The NASWA reprints service offers around 250 collections of past articles on all sorts of shortwave DX related topics. Among the reprints, there is an excellant article by John Bryant and Dave Clarke on tropical band propagation that is MUST reading for anyone who wants to understand listening on the tropical bands. If you seriously want to listen to the tropical bands, joining NASWA is a very necessary first step.
Don Moore
MOORE@tmu1.mcrest.edu
Davenport, Iowa, USA
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