1994 WRTH Review
World Radio / TV Handbook
Kiwa Active Mediumwave Loop
These radios were built to last, but they were also expensive in their time. That is certainly the approach Kiwa Electronics had made with their new table mediumwave loop. It not only works well, but it is a sound and beautiful piece of engineering ... the photograph in the brochure doesn't do it justice. Mediumwave loops were common in radios before the discovery that ferrite material would concentrate radio signals and thus reduce the antenna to a small rod inside most transistor radios.
During the Second World War, the loop became popular in occupied Europe. In simplified terms, you made a wooden frame by nailing two pieces of wood together in the shape of a cross. Then you wound insulated wire around the frame and connected them to the back of the radio. The advantage of a loop, compared to say a random length of wire hanging out of the window, was simple. A loop is highly directional.
That was important in occupied Europe when programs from governments in exile were broadcast over BBC transmitters. At the same time, jamming stations operated by the Nazis were busy trying to drown out the signal by broadcasting noises on the same frequency. By carefully rotating the loop of wire, many listeners were able to reduce the level of jamming interference to a point where the resistance message was at least intelligible.
If you want to listen to distant mediumwave stations, then the loop is probably the best antenna you can use. Clubs like the Medium Wave Circle in Britain, or the International Radio Club of America or the US National Radio Club all offer plans on how to build your own. But you will have to work very long hours to build something quite as smart as the Kiwa Loop.
What is unique about this antenna is the balanced regenerative feedback design which allows you to adjust the bandwidth of the loop down to just 2 kHz. The smaller you make the bandwidth the larger the gain of the antenna. This bandwidth control is extremely useful if you have several strong local mediumwave stations in the neighbourhood and you want to try and pick up stations on adjacent channels. In addition, there is a liquid filled compass on top of the antenna. If you follow the instructions carefully you can actually make bearing measurements on the incoming signal.
It's clear from readers' comments that many people don't understand just how much electrical noise there is floating around inside the average house. The wiring in the house may be radiating all kinds of noise which is picked up along the route. Devices with computers inside them or fluorescent light bulbs are other problem sources, plus television sets either in your house or next door. If you're going to get any use out of a mediumwave loop like this you have to use it in an electrically quiet part of the house. There is no magic way to cancel out local interference.
Practical TestsOnce you have found a spot for the antenna you need to connect it to the control box. A 2.2 metre gray cable comes out of the loop and plugs into the back. Like the loop, the box is heavy-duty and consists of four controls, plus the power switch. The antenna requires 12 volts DC using the mains adapter (included) or from a car battery. You can plug up to two receivers into the back of the control box and there is no problem in isolation between the two.
Using the antenna is a "knob-twiddlers" dream. After some rough adjustments, best reception is obtained by fine tuning the loop, adjusting both the direction and the angle of tilt, and reducing the bandwidth with the regeneration control. It takes some practice to get the sequence right, but it is worth it. We used the loop at two locations in Europe, one very near to a 400 kW mediumwave transmitter. With that kind of power it wasn't possible to null out the powerhouse signal completely, but the channels 9 kHz to either side of the local signal were splatter free and could be peaked. The loop is clearly well designed against overload.
More interesting were the test on "graveyard" channels, i.e. frequencies used by several stations in various countries. Tuning 1458 kHz at a location in The Netherlands it was possible to separate British stations in London, Manchester and Birmingham with ease. The secret is to use the combination of direction, as well as the loop's ability to tilt. The results were clearly better than a reference ferrite rod we used for comparison. The use of Teflon on the pivot points makes it very easy to turn the antenna a fraction in either direction. That is often enough to peak the wanted distant signal long enough to identify it or follow what is being said.
ConclusionsThe Kiwa mediumwave loop antenna is not cheap. At US$360 this antenna is clearly for the enthusiast who takes AM broadcasting seriously. You need to have an electrically quiet place to put the loop and a reasonable communications receiver if the investment is going to be worthwhile. That said, we're delighted that Kiwa has put this excellent antenna on the market. With the sunspot minimum approaching, this is the time to rediscover the secrets between 0.5 and 1.7 MHz. This product really does deserve this year's WRTH Industry Award.
Kiwa Electronics503 7th. Ave. N.E.
Kasson, MN 55944 USA