A thread on rec.radio.shortwave started with a complaint about poor performance from the Degen DE31 active loop antenna. I and some others posted our thoughts on the DE31, and noted that the wires needed to be connected a certain way. A few posts later, the thread originator followed up to say that this solved the problem, and he retracted his complaints about the antenna. This article will explain how loop antennas work, summarize my experiences with the DE31/KA31 antenna, and provide links that were shared in the newsgroup thread.
The Degen DE31/Kaito KA31 active loop antenna amplifies the magnetic component of a radio wave without amplifying the electrical component. As the electrical component is usually comprised of local interference, this process strengthens radio signals with clarity. The loop consists of a wire running through a thin gray rope. Structure for the loop is provided by a horizontal telescopic bar, which is not a receiving component of the antenna.
This antenna is called an active antenna because it receives power from two AAA batteries. An email from Kaito USA told me that "decent" batteries would last over 100 hours. The Duracell AAA batteries that I installed in my DE31 in late 2005 are still working and producing around 1.45 volts each.
The pieces of this product can fit together more than one way, so it is important to follow the product diagram to get the intended performance. The long wire goes between the antenna loop itself and the tuner box. This positions the power source far from the loop, but it places the power switch and tuner dial close to your radio.
Visit the Kaito KA31 product page to see a diagram of how the pieces fit together:
* Kaito KA31 Shortwave active loop antenna
In some cases, clipping this antenna to the whip of one of my radios can strengthen the signal to a usable level. When I use the antenna unpowered, it's acting as a random length wire antenna. (The phrase "random length" refers to the fact that the antenna length has no specific relation to the desired wavelength.)
When I turn on the tuner, I can boost the signal after tuning the antenna to find the right spot. It depends on the signal and the conditions as to whether powering the loop antenna will provide a benefit in my case. My understanding is that the tuner operates in a linear fashion across its supported range (3900 - 22000 khz). Using a small tuning range to map to this large frequency range means that tiny adjustments are required to find the best setting for each frequency.
My loop antenna hangs in a window, with the hole facing north/south. I have not tried rotating it to face east/west, because it's not convenient for me to hang it that way. Regarding how to position a loop antenna, the Radiointel antenna review that is linked below noted that changing the direction of a loop antenna had more of an effect on nulling local interference than increasing or decreasing radio signals. Shortwave signals traveling large distances to reach you will cover a wider area than interference caused by a nearby electrical device.
Here's a Radiointel review where Sony's AN-LP1 loop antenna is compared to the DE31/KA31 loop antenna:
* Degen DE31 vs. Sony ANLP-1 Active SW Loop Antennas
The thread on rec.radio.shortwave also produced some images showing the insides of the DE31 tuner:
If you want to learn more about loop antennas, I recommend the radio antenna Wikipedia article:
* Antenna (radio)
Thanks to craigm, danr_18, Jim Hackett, N9NEO, and Telamon for participating in the DE31 thread with advice and links.