Utility Stations

Besides the broadcasting stations and ham radio, there is other kind of stations transmitting in shortwave: they are the so-called utility stations, that indeed congregate a wide range of services (aeronautical, maritime, fixed, mobile, time signals, among others). The main characteristic of these emissions is the fact that their are directed to specific audiences, transmitting without obey a predetermined schedule (except obviously time signal emissions). The utility stations are not limited only to transmissions using shortwave, they are present in several parts of the radiofrequency spectra, with each service having its own allocation, and with its use being strictly controlled (against broadcasting transmissions on shortwave, where some stations transmit in out-of-band frequencies).

The transmission modes that are utilized vary, depending on the service. For radiophony (voice signals) it is commonly used SSB transmission (LSB or USB) For radiotelegraphy it is used continuous wave (CW), that employs Morse code. Yet the transmissions in radio teletype (RTTY) and fac-simile are realized in digital mode, by using several types of modulation: FSK, DPSK, PSK, etc.

The listening of most of utility stations demands receivers that at least offers continuous coverage of the spectrum. The receivers known as "scanners" are the most appropriated, because they covers pratically all the radiofrequency spectrum. However, receivers utilized for shortwave broadcasting reception that at least cover frequencies between 150 kHz and 30 MHz and offers SSB/CW tuning, are also appreciated.

The utility stations can be divided into fixed and mobile services:

• mobile services: terrestrial mobile stations, ships, aircrafts, NDBs (Non-Directional Beacons).
• serviços fixos: time signal and standard frequency stations, meteorological stations, geophysical information stations, number stations, radioshipping systems.

It follows a brief description of the main services available: Eis uma breve descrição dos principais tipos de serviços existentes:

• aeronautical service: this service has the purpose of establishing a communication between aircrafts and terrestrial stations. The transmission is almost totally made in radiophony (in USB mode), in simplex mode. Frequency bands were allocated in the HF spectrum for use of aeronautical communications; however, in areas with a high traffic density, the transmissions are realized in the VHF band (118-136 MHz). Examples: communication between aircraft and control center, fixed aeronautical communications, VOLMET stations, Acars.
• maritime service: this service comprises coast stations and mobile maritim stations, transmitting in frequency bands in the MF and HF bands (i.e. medium wave and shortwave), including the international frequency for distress and safety at 2182 kHz. These stations transmit in duplex mode, therefore using two frequencies to establish a communication. Examples: maritime safety stations, communications between ships and coast stations.
• point-to-point: it consists of those services that have the purpose of establishing a communication between two defined, fixed points. The point-to-point stations are included in the fixed service (excepting the aeronautical and maritime fixed stations). Examples: police communications, radio-taxi, meteorological stations.

As the broadcasting stations, the listening of utility stations can also be confirmed by means of verification letters of QSL cards. The major difficult in obtaining a confirmation from a utility station is to know the address for where the reception report will be sent, because these stations never inform the address during its transmissions, mainly due to the fact that the transmissions are directed to specific audiences, that don't need to report the reception conditions to the utility station. A solution is searching information on the Internet, in DX clubs, in specialized publications, or consulting other listenets, in order to get the station's address. The reception reports cannot have details about the transmission contents, because the transmissions are not destined to the general audience, and can consist of privative communications or contain reserved information (except time signal and standard frequency emissions). Besides, the legislation in most countries avoids the divulgation of any communication not destinated to general audiences. Only basic data can be reported: who's contacting who, date, hour, frequency, transmission mode. Also, it is included a detailed description of the reception conditions, being utilized the RST-code to evaluate the reception.

The beginners in the utility listening can first try listen to time signal stations. In contrast with the other types of utility stations, the time signal stations don't transmit to restricted audiences, with their transmissions reaching large areas, by using known frequencies in the HF band, easily listened. Besides, almost of these stations confirm the reception reports with QSL cards. Other type of transmission easily listened is NDB, that consists of continuous transmissions of simple codes in CW.