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DRM radio

After many years of stagnation, DRM is emerging as a perfect fit for shortwave broadcasters seeking to increase their audience, and at the same time reducing their energy consumption.

DRM is an open source, non proprietary standard for terrestrial broadcasting, promoted by the DRM Consortium, a group of transmission equipment and receiver manufacturers as well as international broadcasters.

Over 30 broadcasters from around the world now carry DRM broadcasts. The latest schedule can be found here: http://www.hfcc.org/drm/

To receive DRM broadcasts a suitable receiver is required. The GR216 receiver, https://www.tecsunradios.com.au/store/product/tecsun-drm-radio/, promoted by Tecsun Radios Australia is a high-performance receiver, both on DRM and analogue shortwave. It is a self-contained unit, with provision for the connection of external antennas for shortwave and FM.

The receiver includes a self contained linear power supply which eliminates interference caused in  receivers powered by switch mode power supplies.

drm radio australia

 

We recommend an external antenna for good DRM reception and our MW/SW Outdoor Antenna  https://www.tecsunradios.com.au/store/product/tecsun-shortwave-outdoor-antenna/ is most suitable. This antenna incorporates a 9:1 balun to provide the correct impedance for most shortwave receivers with an external antenna socket.

antenna shortwave drm

The typical improvement over the same length of wire without the matching components is between 10 and 15dB in signal level.

A word about antennas:

Directional characteristics of random wire and long wire shortwave receiving antennas are dependent upon the antenna length, height above ground, received frequency and directional orientation of the antenna wire. The four elements are interactive.

Generally the antenna should be aimed so that the transmission source is at 90 degrees to the antenna. So if the transmission source is to the West, run the antenna on a North South direction if possible. This works best on antennas that are less than a quarter wavelength in length and mounted a quarter wavelength above the ground (such as the antenna mentioned above).

In the case of a simple longwire without matching, the length of the wire cut for one quarter wavelength at popular DRM frequencies is as follows:

13Mhz: 6 metres in length, 15Mhz: 5 metres in length, 7 Mhz: 10 metres in length

A simple long wire antenna will work better at greater elevation above the ground, ie the higher the better. Multistrand insulated wire will work better and for longer that solid copper wire, which will weaken with repeated movement.

In practical terms, a DRM receiver with an external antenna will be able to hear most current DRM broadcasts from 13-18Mhz. Check the broadcasting schedule for the appropriate times.

Remember that all times are given in GMT and that means AEST (Australian Eastern Standard Time) is 10 hours ahead of GMT. Hence (for example) the BBC Relay from Singapore on 15620Khz will appear between 2pm and 8pm AEST.

One more factor that can influence the success of your reception is the direction in which the signal is being beamed.

This information is also available on the DRM HF schedule site. If you are in the target area you will have a much better chance of sucessfully receiving DRM broadcasts.

Target areas can be seen here: https://www.drm.org/what-can-i-hear/broadcast-schedule-2/

There are many stations that can be received if suitable attention is paid to antenna orientation, and broadcasting schedules, with more stations being added to the schedule every month.

Good Listening !

In 1843 the phenonema known as the Solar cycle was discovered by Samuel Schwabe a German astronomer who observed transitions of the Sun from periods of high activity to low activity every 11 years, over a period of nearly 20 years.

Put in simple terms, the Sun is composed of a huge ball of electrically charged hot gas. As this gas moves, it generates a powerful magnetic field. This magnetic field transitions through an 11 year cycle (known as the Solar Cycle) during which the magnetic poles of the Sun are transposed, ie the north and south poles change places.

This cycle affects activity on the surface of the Sun, such as sunspots and solar flares. The energy released by these events charges particles in the ionosphere, affecting radio propagation. More solar flares and sunspots occur at the peak of the cycle than at the bottom of the cycle. Typical values are 80-100 sunspots at the cycle peak and 15 or so at the cycle minimum.

When a strong flare occurs, the increased x-ray and extreme ultraviolet radiation produces ionisation in the lower, D (absorption) layer of the ionosphere, disrupting HF radio broadcasts by absorbing rather than reflecting signals. 

We are currently at the end of Solar Cycle 24 (calculated as mid 2020), and from this point we can expect an increase in solar activity and changed radio propagation as the maximum useable frequency (MUF) for shortwave communications increases with an increase in solar activity.

At the peak of the Solar Cycle, the higher frequencies of the shortwave spectrum are very good. Low power stations can be heard over remarkably long distances. 

At the bottom of the cycle, the current position, those higher frequency signals will not usually support normal propagation via the ionosphere. So propagation at lower frequencies will be better whilst higher frequencies will suffer. 

 

Article written by Tecsun Radios Australia

Image of sun via Nasa.