HRS type antennas
are more or less the standard antenna
used for long distance high power shortwave
broadcasting (> 1000 km).
History of HRS design
HRS antennas were discovered during the 1920s, and as such were not originally intended for voice and music broadcasting.
However, the directional properties of this antenna type were ideal for voice broadcasting -- and the design is now pervasive in international broadcasting by the 1950s.
As far back as the mid-1930s, Radio Netherlands was using a rotatable HRS antenna for global coverage.
A versatile antenna type
Important technical variations in HRS antennas
- HRS type antennas come in two types, fixed and rotatable.
- About 80% of all commissioned HRS type antennas in use today are fixed azimuth.
- Electrical slewing allows a fixed azimuth HRS antenna beam to be moved by as much as 25 degrees, however most designs only allow for 15 degrees.
- Only one type of HRS rotatable antenna is coupled with a building that houses a transmitter -- the ALLISS system.
What are HRS type antennas?
The curtain antenna is a dipole array, consisting of rows and columns of dipoles.
- The curtain antenna is a high gain directional antenna, that is designed for medium and long range shortwave communications.
- The HR(S) notation is as follows
- HR Rows/Columns/Wavelength(s) -- Above Ground
How to interpret HRS notation
An HR 4/4/1 antenna has the following characteristics
- 4 rows
- 4 columns
- is 1 wavelength Above Ground (with respect to mid-band transmission frequency)
Syntax note: HRS
- The S means is that the antenna's pattern is electrically steerable.
- Electrical steering is typically done in the horizontal orientation, with some adjustments being possible in the vertical domain.
- Electrical steering of the antenna beam typically is limited to (-/+) 15° in the vertical, and about 5° in the horizontal.
Notes on HRS notation
HRS transmission systems can be "double sided", but in this case HRRS notation is used. The extra R meaning "Reversible". Very few HRRS antenna systems are in use worldwide.
- HRS antennas of type HRS 1/1/1 are undefined.
- HRS antennas of type HRS 1/2/1 and 2/1/1 exist, but see little practical use in broadcasting.
- The number of rows can be 2, 3, 4, 6, 8 or 12.
- The number of columns is usually 2, 3, 4, 6 or 8.
- The dipoles are ALWAYS horizontally polarized.
- A reflector screen is placed behind the dipole array so as to provide a directive beam.
- For a 2-wide dipole array, the beamwidth is around 50°
- For a 3-wide dipole array, the beamwidth is around 40°
- For a 4-wide dipole array, the beamwidth is around 30°
The main beam can be slewed by 15° or 30° so that a maximum
coverage of 90° can be achieved.
Vertical Launch Angle
The number of dipole rows and the height of the lowest element above
ground determine the elevation angle and consequently the distance to the service area.
- A 2-row high array has a typical takeoff angle of 20°
- is most commonly used for medium range communications.
- A 4-row high array has a typical takeoff angle of 10°
- is most commonly used for long range communications.
- A 6-row array is similar to a 4-row, but can achieve 5° to 10° takeoff angles. This antenna type can be used in shortwave communications circuits of 12000 km, and is highly directive.
Variations of HRS antennas
Curtain antennas are available in two sizes.
- A low band array typically covers the 6, 7, 9 and 11 MHz bands.
- Low band antennas are typically larger and taller.
- A high band array typically covers the 11, 13, 15, 17 and 21 MHz
bands (or 13-26 MHz bands).
- High band antennas are typically smaller and shorter.
Transmission system optimization for geopolitics
- Occasionally an international broadcasters may use, for reasons of geopolitical necessity -- a highband, midband as well as lowband HRS curtain arrays.
- Using 3 HR curtain arrays to cover the HF broadcasting spectrum creates a highly optimized HF transmission system.
- HF transmission systems using 3 or more curtain arrays can be costly to build and maintain.
- Since the mid 1990s no new HF relay stations have been built.
- Existing HRS shortwave transmission systems (built before 1992) will likely remain in use for many years. The modern HRS antenna design thankfully has a long lifespan.
Examples of HRS antennas
This is an example of theoretical HRS design shortwave relay stations. This may help one better understand HRS antenna directivity.
A proposal for a Radio Canada International relay station to be constructed in Tofino-Ucluelet found at http://cbc.am/rci-bc.htm
Shortwave relay stations using only HRS antennas
This is a list of stations using only HRS antennas, sorted by country name.