By Jason Reilly.....

 

There’s something fascinating about listening to distant stations. I’ve recently developed a taste for listening to distant AM broadcast band stations. There’s several advantages to this: most of the stations nearby speak your local language, and you can be guaranteed hearing stations from quite some distance away of a night time. Hearing distant stations is easy, but hearing really distant stations on this band is quite a challenge. I find it truly fascinating to listen to the adverts for businesses in locations from another state, even another country, to listen to the different announcer styles and the variety of other local programme content.

 

 

AM broadcast band DX’ing is something that anyone can do… there’s an abundance of suitable receivers around the home that you can use, even your bedside clock radio! It’s a hobby that you can do on the move, too – most car radios have a reasonably sensitive receiver; imagine doing some DX’ing on your way to work or shopping each day… but in general you’ll find such activities are most convenient at home or in a nice quiet spot where you can sit down and concentrate. As you get more experienced with DX’ing the AM broadcast band, you’ll find that some accessories are very helpful. A good pair of enclosed headphones are vital for keeping external noises and distractions from hearing a weak station that you’ve been trying to identify for the last half hour. A good portable radio becomes another must have… and shortly after that you find yourself looking for a better antenna. At such long wavelengths, you need to make use of some unconventional antennae. One such antenna is the loop antenna, which has several advantages: they’re small, directional, tuneable and quite effective.

 

 

While there are many designs for loop antennae on the internet, not everyone has either the tools, materials, time or inclination to go making one. There are pre-assembled loop antenna that you can buy, some quite expensive, some quite cheap. Having already seen how effective and capable some of the ‘cheap’ Chinese brand radio receivers can be, I decided to check out how good a ‘cheap’ AM broadcast band loop antenna can be. Tecsun make a small AM loop antenna, called the AN-200. Its quite small, being about 25cm in diameter, and its quite neat too. Unlike other loop designs it doesn’t look out of place in the modern décor of a home. Being tuneable over the range of about 510 to 1750 kHz, it covers the entire band used both here in Australia, and the extended band in use by some ‘narrowcasters’ and in other countries between 1610 and 1700 kHz.

 

 

There’s really not much to describe about the loop antenna itself. It has a knob to tune the antenna to your desired station, and a 3.5mm audio connector to permit direct connection to a radio antenna input. Using the loop is simplicity itself. You tune your radio to the frequency you want, place the loop near your radio, and then turn the knob slowly on the AN-200 until the background noise (or the tuned radio stations signal) reaches a peak. The loop antenna doesn’t have to have any direct connection to your radio! The signal is transferred to your radio by inductive coupling. Every radio will have a ‘sweet spot’ where you will get maximum signal transfer into your radio, and once you find that sweet spot on your radio, it will always be the same no matter what frequency you tune into. As you tune the AN-200 into your tuned frequency, you’ll find the peak is very sharp, and that nearby frequencies are quite well rejected by the antenna; the antenna can add a healthy level of pre-selection to your radio. This, combined with the directional characteristics of the antenna can even help you dig out a weak station that is being wiped out by an adjacent strong local radio station. Notice that above I mentioned the 3.5mm audio connection for the loop antenna? A loop is quite high in impedance, and best results come from using a high impedance input on a radio. I have such an input on my Jaycar AR1747 receiver, and making that connection to the loop directly didn’t produce as good results as just placing the loop nearby the radio and rely on inductive coupling, which was surprising.

 

 

When you use the loop, you’ll find that it picks up best in two directions – and will reject signals or noise in two directions at right angles to the direction of maximum signal pickup. The directions of maximum pickup is a line along the edge of the loop, and the directions of the nulls are at 90 degrees, with the loop ‘facing’ the directions of minimum pickup. Usually, its best not to peak a signal for maximum signal strength, rather its best to go for minimum noise or interference, using the nulls to reduce the pickup of any noise sources or interfering stations. Peaking for maximum strength during the day when signals are weaker and there’s fewer interfering stations is OK, but of a night the ability to null out interfering stations is very handy indeed.

 

 

So how well does the AN-200 work? Very well indeed! During the day, a signal that is barely audible can be bought up out of the noise to be quite pleasantly listenable. Stations that you wouldn’t even be able to hear at all without the loop become audible, though somewhat noisy. Who would have thought that many Victorian AM radio stations, and a few South Australian and NSW AM radio stations could be audible in the middle of the day in Tasmania? The Tecsun AN-200 delivered the goods without any fuss. Of a night time, the loops effectiveness becomes a little less pronounced as signals are generally stronger and more abundant anyway, but it can still be quite useful in some situations.

 

 

Now after all that, are you wondering where you can get a Tecsun AN-200? Why, eBay of course! Seller “liypn” sells them for USD $15, plus USD $21.50 postage to Australia. Considering the time and effort it could take to make your own loop antenna, and then considering that it probably wouldn’t be as neat or attractive as the AN-200, I think it represents excellent value. If you are into receiving distant AM radio stations, I think this is a must-buy!