The warm, inviting glow of vacuum tubes has been replaced with digital displays, but the allure of shortwave listening is unchanged. Before the internet, shortwave broadcasts gave us a window into other countries and cultures. That window is still open today with an HF desktop radio.
What are the HF bands?
The high frequency (HF) bands are just above the AM broadcast band, extending from 3MHz to 30Mhz. International agreements subdivide this into broadcast, amateur, maritime, military, and aviation segments.
How does it work?
Radio waves bounce off the ionosphere, an ionized layer in the atmosphere that moves higher at night, allowing radio frequencies to travel longer distances. The eleven year sunspot cycle changes radio reception also, but primarily affects the upper end of the HF band.
What can you hear?
Several different transmission modes are used on the shortwave bands, though not all receivers are equipped for them. They include: AM, single side band (SSB), Morse code (CW), narrow and wide FM, radio teletype (RTTY), and data transmissions. The simplest HF desktop radios often receive only the AM and FM broadcast bands.
Broadcast content includes: news, sports, weather, music, language lessons, religious broadcasts, propaganda, and even hate-filled diatribes. All are AM. Many programs are broadcast in English and are beamed toward North America in the evening hours.
What equipment is needed?
Shortwave receivers range from simple and inexpensive to breathtakingly complex and expensive. The high-end equipment is much better at picking up weak signals and separating them from background noise, but if you only listen to international news broadcasts, an inexpensive receiver is adequate. Units with a digital frequency display are a step up from those with mere dials, and they are generally more stable, meaning that the receiver will not drift off frequency. They do this with a phase-locked loop (PLL).
More adventurous folks may consider building a regenerative receiver from a kit. This design was common prior to the Second World War and requires modest skill to build and use. They have excellent sensitivity and selectivity, the ability to detect weak signals and select between closely spaced transmissions.
An outside antenna is a plus for any shortwave receiver, but strong local stations can overpower the filters in an inexpensive receiver, causing interference. If you plan to listen to international shortwave broadcasts and your present antenna is adequate, there’s no need to upgrade. Experimenting can be fun, though, so don’t hesitate to try a random wire antenna or even a metal window frame. If you do install an outside antenna, be sure to include lightning protection to prevent damage to your radio and home.
