1950 - Medium Wave Radio Propagation Research

The study and research into long-distance radio propagation have been amongst my major continuing objectives since the early 1950s, at the hobby and professional levels.

This interest had formed the backdrop on my long-term involvement with radio communications and transmission.

My initial interest was shaped by medium-wave propagation observed at the family's weekend bungalow at Altona, west of Melbourne, in 1950, and pursued until the early 1990s from Mont Albert and on field trips to many rural locations.

In 1950, at Altona, I recall good mediumwave signals from New Zealand stations in the late afternoon in mid-summer, several hours beforer our local sunset, using an antiquated TRF domestic console radio with a few metres of antenna!

In the 1950s, long-haul mediumwav propagation was excellent in Melbourne, with little or no electrical radio frequency pollution or noise.

The concept of 24-hour broadcasting was relatively unknown in Australia in those years, with only two such broadcasters operating all-night.

In the 1970s, all-night broadcasting had become popular as stations sought ratings and greater financial revenue from advertising dollars.

This meant that the band was becoming heavily congested by increasing numbers of higher powered transmitters operating in Australia, effectively blocking a greater number of channels.

To partially overcome these technical problems, some of us built directional Box or Spiral Loop antennas,which allowed "nulling" of interfering co-channel, or adjacent channel signals.

Enthusiasts also experimented with very long antennas known as Beverage Antennas, which were strung out in open paddocks, and terninated at the distant end, often hundreds of metres away..

The Beverage Antenna is a relatively inexpensive but very effective long-wire receiving antenna for longwave, mediumwave, shortwave,and military reception. Harold H. Beverage experimented with receiving antennas similar to the Beverage antenna in 1919 at the Otter Cliffs Radio Station.

By 1921, Beverage long wave receiving antennas up to nine miles (14 km) long had been installed at RCA's Riverhead,. New York, Belfast, Maine, Belmar, New Jersey, and Chatham, Massachusettss receiver stations.

The antenna was patented in 1921 and named for its inventor Harole H. Beverage. Perhaps the largest Beverage antenna - an array of four phased Beverges three miles (5 km) long and two miles (3 km) wide - was built by AT&T in Houlton, Maine, for for the first trans-Atlamntic telephone system opened in 1927.

While these antennas provide excellent directivity, a large amount of space is required. Beverage antennas are highly directional and physically far too large to be practically rotated so installations often use multiple antennas to provide a choice of azimuthal coverage.

A Beverage consists of a wire one or two wavelengths long (hundreds of feet at HF to several kilometres for longwave). A resistor connected to a ground rod terminates the end of the antenna pointed to the target area, a 470 ohm non-inductive resistor provides excellent results for most soils. A 50 or 75 ohm coaxial transmission connecs the receiver to the opposite end of the antenna through an impedance-matching transformer. Some Beverage antennas use a two-wire design that allows reception in two directions from a single Beverage antenna. Other designs use sloped ends where the centre of the antenna is six to eight feet high and both ends of the antenna gradually slope downwards towards the termination resistor and matching transformer.

Prior to 1975, Australian MW stations operated on frequencies on multiples of 10 Khz, ending in "0". European, Middle Eastern, and African stations used frequencies separated by 9 kHz, which meant that judicious tuning and use of a Loop or Beverage antenns could yield excellent results. Stations in the Americas used 10 kHz channel spacing, same as in Australia.

This resulted in some splendid MW reception from Europe, the Middle East and Africa during our early morning hours, up to sunrise.

All that changed in 1976, when stations in ITU Region Three, which included Australia and New Zealand, were required to shift their operatiions to the 9 kHz separation, identical with Euripe, the Middle East, and Africa. American stations stayed with the 10 kHz separation.

By that time, the MW band in Australia had become heavily congested, with most commercial stations operating 24 hrs. Some channels were occupied by as many as six stations, in various States. The ABC then decided to put most of its stations on to 24-hr operations.

This meant that long-distance mediumwave reception in Australia became a very specialized activity from the mid-1980s, and at a hobby level, interest from enthusiasts dropped away considerably.

The increasing level of power-line noise, general RF pollution, and spurious signals on the mediumwave band were also major inhibiting factors.

Exceptions were for hobbyists located in rural or outback areas, ell away from RFI sources, with the space to erect long Beverage installations or experiment with Loop antennas.

In 1993, I was forced to end my involvement in long-distance mediumwave propagation reaearch, due to the combination of factors described above, and I dismantled my Box and Spiral Loops.

My mediumwave "career" had spanned nearly 45 years, and in that time I had accumulated 551 QSL Verifications from stations in 113 "radio countries"

I had written many technical papers on the subject, which were published in various sources, including the World Radio TV Handbook.