General term in the
shortwave radio listening (
SWL) community for
frequencies between 2000 - 5000
kHz.
Far from being a
wasteland, the tropical band contains a number of significant
radio services.
Utility stations, such as
teletype and
navigational systems (LORAN) provide
governmental,
nautical, and
commercial communication. Use of radio navigational systems has declined with the advent of
Global Positioning System technology.
Listeners will also find
clandestine stations in two categories. First are low powered
propaganda stations from international
hot spots such as
Afghanistan or
East Timor. These stations operate on their local time, so certain regions will not be accessible during every week due to poor
propagation at the receiving station. Secondly, some nations operate
numbers stations, or streams of numbers transmitted by voice (usually an utterly
ethereal female voice). Prevalent in the
Cold War era, numbers stations are still employed by nations such as
Cuba.
Finally,
Central and
South American broadcasters operate low power stations within the tropical band. These stations are run on a
shoestring and are intended for local audiences only. Most are music stations and
religious broadcasters with some propaganda stations. As a
fringe benefit tropical music stations provide great
entertainment and exposure to music seldom heard elsewhere.
The challenge is to log the Central and South American stations when active in local
prime time. Add to the mix propagation changes and the measly 1 kW power levels of the strongest stations. For comparison,
BBC World Service to
Europe and the
Mideast broadcasts at 500 kW or more. Tropical band
DXing might be characterized as the
double black diamond of
SWLing.
Since broadcasters use longer
wavelength frequencies, listeners will find the best listening in the
Northern Hemisphere during the
winter months. I suspect that the optimal season patterns in the
Southern Hemisphere mirror the Northern Hemisphere, converting to
summer from
winter respectively. Best reception occurs during local
dusk, or the
grey line effect. Reception remains strong for another three hours or so, but erodes completely by local
midnight. Listeners utilize computer software (such as
Geoclock) to predict grey line as represented by a creeping
bell curve of night's progression around the world.
Although not necessary,
tabletop receivers provide for optimal tropical listening. These
breadbox-sized recievers require
outdoor antennas.
Use your imagination when crafting antennas. Favorites include
dipoles,
wire arrays, and electrified "
active antenna" loops for
cliff dwellers. I spin my own antennas, joining them to various ancient
ham radio gear and an
Icom R75 modern receiver.
Vacuum tube radios emit rich tone when tuned properly and with fresh tubes, but tube sets found at
hamfests and elsewhere usually require much
restoration.
Here's to
soldering burns!