Magnetic Loop antenna with tripod by Alpha

QRP Magnetic Loop Antenna with Tripod

Coax Loop by Alpha Antennas Alpha Antennas Loop

The Alpha Antenna (USA) Magnetic Loop is a portable antenna for a maximum transmit power of 30 W PEP SSB. The antenna comes in a handy transport bag and includes a tripod which has an extended height of about 100cm. With the help of this tripod the antenna can be installed nearly anywhere in the field. The assembled antenna can be tuned from 40 to 10m, the signal is injected with the help of a secondary so called Faraday loop, to which the feedline is connected. This inner loop as well as the outer loop is made of LMR 400 coaxial cable, where the outer shoield is used as a thick conductor with large diameter. The outer loop is mounted to the capacitor box with high quality coaxial connectors.

The tuning of the antenna is done by means of a variable capacitor, which is installed in a solid box. The drive of the capacitor uses a reduction and allows very precise tuning. To minimize the effects of capacitive influence of the body and to reduce the risk of HF burns the drive shaft is made from non-conductive nylon. The antenna has a comparatively high efficiency by using only one butterfly capacitor and by placing the tuning components directly inside the large loop.

The tuning process is very simple: first tune for maximum noise while listening on or near the desired frequency, then you transmit with low power and adjust the capacitor for minimum SWR by watching the built-in SWR meter of the radio. As an additional help the manufacturer has provided a light (gas discharge lamp) in the tuning box, which extinguishes at minimum SWR (this method requires a minimum of 5W transmit power). With a little practice an SWR of 2:1 or better can be achieved.

By their very nature magnetic loops are quite narrow banded by the hi Q of the resonant circuit. The manufacturer claims a usable bandwidth of 20 to 100% of the ham radio band without retuning: 200 kHz on 10m, 40 kHz on 12m, 150 kHz on 15m, 80 kHz on 17m, 70 kHz on 20m, 50 kHz on 30m and 40 kHz on 40m (all values approximatively). The narrow bandwidth is also beneficial for the receiver, the antenna works like a preselector!

The diameter of the assembled loop is 85cm, the large loop forms slight ellipse. The HF feed is done via a short coaxial cable, which is connected to the inner loop. Included in shipment is a very useful nylon carrying bag with a size of 30 x 30 cm. The low weight of less than 2 kg makes the Alpha Antennas Loop a perfect companion for portable operations, field day use or vacations.

Order No.
11479 Alpha Antennas QRP Magnetic Loop Antenna for portable operations 378.00 € Temporarily not available
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