The international service of Czech Radio 
2-7-2015, 23:08 UTC
Shortwave transmission
  The traditional way to listen to Radio Prague is on shortwave. You can hear us in many parts of the world, and all you need is an ordinary radio that includes shortwave. This is still the most widespread way of listening to international radio stations, including Radio Prague.

What is Shortwave? / What Kind of Receiver Do I Need? / Which Receiver is Better?
Is a Special Antenna Necessary? / How to Select a Frequency / How to Listen to Us

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What is Shortwave?

Radio waves are a type of electromagnetic radiation, just like light, for example. For radio broadcasting, the frequencies used run from hundreds of kilohertz to hundreds of gigahertz (a million kilohertz). This wide spectrum is divided into bands. The lowest frequencies are longwave (LW), then comes mediumwave (MW), short waves, very high frequencies (VHF), and so on. Long- and mediumwave are used for broadcasting to a distance of a few hundred kilometers (at night the range is greater). VHF and still higher frequencies provide very good reception, but their range isn't much greater than line of sight from the transmitter (about 100 km.).

Shortwave isn't exceptional in it's wavelength, but in the method of transmission and coverage. Short wave radio energy directed away from the transimitter is partly deflected and sent back to the Earth's surface by the ionosphere. It's thus possible to send a signal a great distance. A disadvantage of this method of transmission is that the properties of the ionosphere are continually changing over the course of the year, in the multi-year cycles of solar activity and even over one day, along with the quality of reception.

Several bands denoted by frequency or by wavelength are assigned to radio broadcasting on shortwaves (the higher the frequency, the shorter the wavelength):

Wavelength (in meters)Frequency (in megahertz)
49m6 MHz
41m7 MHz
31m9 MHz
25m11 MHz
22m13 MHz
19m15 MHz
16m17 MHz
13m21 MHz
11m26 MHz

What Kind of Receiver Do I Need?

Analog Receivers

There are two main types of receiver, depending on how they're tuned: analog and digital. The disadvantage of analog receivers is the discomfort of tuning. The desired frequency is tuned in by turning a dial. It does have a higher level of gradation by which the frequency can be adjusted, but it is still imprecise.

An analog receiver should have shortwave divided into individual bands or at least groups of bands. If a lot of shortwave bands are on one dial, stations will be very close to each other on the dial and tuning will be very difficult.

Receivers with Digital Tuning

Digital receivers usually have a diplay on which the frequency appears. This is set by a numerical keypad, or raised and lowered in steps with buttons or a dial, and frequencies for stations can generally be put into memory. Tuning is thus simple, fast and precise.

Which Receiver is Better?

From a comfort standpoint, we would recommend a receiver with digital tuning. If it's a question of reception quality, then two characteristics become important: sensitivity and selectivity (the ability to tune out adjacent stations causing interference). Consequently, the quality of reception isn't necessarily determined by the method of tuning.

Ordinary receivers are moderately priced and it pays to invest in a name brand. A receiver should definitely have the ability to receive all the bands listed in the table above. In particular, verify the presence of the 11m (26 MHz) and and 13m (21 MHz) bands, which will become more commonly used in coming years, thanks to the present rapid increase in sunspot activity.

Is a Special Antenna Necessary?

Ordinary receivers usually have their own built-in telescoping antennas. This antenna should in the majority of cases be sufficient. An external antenna can substantially improve reception, if, for example, the receiver is located inside a building with a ferroconcrete structure. First try moving the receiver around the room, however, preferably orienting it toward a window in the direction of the signal's expected origin.

The simplest (and generally completely sufficient) external antenna you can get is to connect several meters of wire to the receiver's antenna input. If the receiver doesn't have a special antenna socket, you can simply wind the end of the wire around the receiver's telescoping antenna several times.

The other end you fasten to some object, non-conductive if possible, outside the building. You can try experimenting with the length of your antenna. A longer antenna doesn't always have to mean better reception. A longer antenna also receives strong interference from surrounding stations (as well as from home appliances, industrial equipment and so on). The input circuit will then become overloaded and lose its ability to separate individual signals.

Broadcast Frequencies

The frequencies on shortwave are indicated in megahertz (millions of Hertz - MHz for short) or more often in kilohertz (kHz, thousands of Hertz). For example, 11,600 kHz equals 11.6 MHz.

Why do stations regularly change their frequency?

It isn't to confuse their listeners. The main reason is the continual changes in the conditions for shortwave propagation. The frequencies suitable for broadcast to certain regions during the winter are difficult or impossible to hear in the summer (and vice versa). Similar changes occur in the alternation from day to night and over the 11-year cycle of solar activity. The majority of stations, including Radio Prague, therefore have a special schedule for the winter season, which begins at the end of October, and for the summer season beginning at the end of March. Some stations even modify frequencies four times a year. Another reason for the changes might be an effort to avoid interference from other stations, a common occurrence.

How to select a frequency

The selection of a frequency depends not only on the time of year, but also on the time of day. It's possible to say, to simplify a great deal, that during the evening and night it's better to transmit on low frequencies and during the day on higher ones. This difference is less pronounced during the summer. Geomagnetic and ionospheric disturbances also have a considerable influence, worsening or disrupting reception for hours or even days at a time.

How to listen to us

Our brief introduction to the problems of shortwave reception wouldn't be complete without mentioning that the majority of shortwave stations welcome reports about the reception quality. As we already said, the quality of shortwave reception isn't as constant as on other radio bands and even the best scientific predictions of shortwave transmissions aren't always accurate.

If you write to our staton the date and time you heard us, along with the frequency you tuned in Radio Prague and what the quality of the reception was, you will have the gratitude of our colleagues who plan and manage the frequencies and check on their effectivness. In addition to this (as if it weren't enough), you will receive a QSL card in the mail, confirming that you tuned in our station. QSL cards are collector's items and have been used since the beginnings of radio broadcast as official confirmations of reception or amateur radio connection.