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Monitoring Times

December 1995

Larry Van Horn, N5FPW

Kiwa Medium Wave Loop Antenna

Most listeners get started in the radio hobby listening to distant (DX) stations in the medium wave (MW) or broadcast band (BCB), and I'm no exception to this rule. In fact, over the last 30 years of radio listening I have never quit DXing the AM broadcast band. While I consider myself an ardent enthusiast of the utility bands in the shortwave spectrum, my favorite band to DX is still the broadcast band.

Over the years I have used a variety of antennas and receivers for broadcast band reception. Longwires, ferrite loop coils, and air-core loops (both commercial and homebrew) have graced my shacks over the years. All of these antennas have been used successfully to add to my station totals and AM BCB QSL collection.

Last year, while reviewing some technical literature I had received in the office, I discovered the Kiwa MW air-core loop antenna. Since the reviews of the Kiwa had been positive, I decided to purchase the antenna and use it during the upcoming AM DX season. After one complete DX season here in Brasstown the results have been nothing short of fantastic.

The Kiwa MW antenna is a high performance air-core loop antenna designed for 530-1700 kHz reception. The antenna has some special features that improve MW reception even in today's crowded broadcast band. The Kiwa loop features a fully balanced loop design that improves nulling ability and provides noise immunity. Electrically balancing the circuitry minimizes the pickup of electrical interference.

A regeneration control on the Kiwa is used as a variable bandwidth control. As the regeneration increases, the bandwidth narrows, and the gain also increases. This control can provide up to 75% bandwidth reduction as it is adjusted from minimum to maximum position. The antenna's electronics has an inherently narrow bandwidth to begin with, all of which helps reduce problems with strong signal splatter from nearby MW stations. If additional bandwidth and audio fidelity is needed, a local/DX preamp switch provides attenuation of strong signals in the "local" position while increasing the antenna bandwidth for improved fidelity.

The maximum -6 dB bandwidth occurs at the top of the band (1700 kHz). That bandwidth is typically 7.5 kHz or 15 kHz. The bandwidth narrows as the frequency decreases. At 650 kHz the -6dB bandwidth is approximately 6 kHz. The regeneration control typically provides a 70-75% reduction in bandwidth from those mentioned above.

One of the big advantages of an air core loop versus ferrite loop coils is the deep nulls obtained by the former. I have two local AM broadcasters (five kilowatts) within five miles of my shack. I am able to null both of these local stations completely, even when they are at full power during daylight hours. I have logged several stations in the null of these locals that I had not been able to hear on any other antenna in my shack.

Another advantage of the Kiwa over a lot of air core designs I have used is that the control surface is separate from the antenna, which makes adjusting the electronics much easier. On older loop designs, the tuning devices are located on the antenna itself. Given the null sensitivity that most air core loops exhibit, it is very easy to knock out all your careful adjustments of azimuth and elevation when you start cranking around on the tuning knobs of the antenna. This is not a problem on the Kiwa.

Most MW listeners are aware that turning a radio with a built-in loop antenna in azimuth can aid in nulling out a local station. But that is not the only axis that can achieve this effect. By moving an antenna in elevation, even deeper nulls are possible. The Kiwa loop tilt control includes a 3 to 1 gear reduction for precise nulling of local signals and interference. You can even change the antenna tilt up to 90 degrees from vertical.

In summary, this antenna has been a welcome addition in my radio shack. I now have heard over 22 states and 150 stations in the broadcast band during daytime hours alone (10 am to 2 pm local time). The Kiwa contributed to my best daytime BCB catch everWOAI-1200 from San Antonio, Texas, (1200 miles) at noon, local time. The receiver I used for this test is an old Drake SPR-4 that I bought at a hamfest for $75.00.

If you want to improve your broadcast band reception on your communications or portable receiver, you should take a serious look at the Kiwa MW air-core loop. This antenna not only looks good, but it is a real workhorse in pulling in MW broadcast band stations.

Kiwa Electronics

503 7th. Ave. N.E.
Kasson, MN 55944 USA
507.634.6134
kiwa@wolfenet.com


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