AMA Magnetic Loops Design DK5CZ 'Käferlein'

The magnetic loop antennas by OM C. Käferlein (DK5CZ, Darmstadt) are well known and popular not only in Germany. The production was later continued by Funktechnik Beese (Darmstadt). In 2016 we acquired the right to the name and all design documents of these fine antennas.

AMA Magnetic Loops - Principle of construction

http://www.njuskalo.hr/image-bigger/radioamaterska-oprema/k-ferlein-ama-9-loop-antenne-magnetic-loop-slika-49440209.jpgThe main feature of a magnetic loop is it's comparably small size in relation to the wavelength. This makes this type of antenna very attractive to many radio amateurs with little space for aerials. The tuning is done with a high voltage capacitor in the loop, which is made from aluminium tubing. For best convenience the capacitor is tuned remotely by an electric motor.

Due to the physical principle of the loop antennas, these antennas have a very low radiation resistance. To achieve a good efficiency the losses in the antenna must be reduced as much as possible. This leads to the following construction requirements for AMA magnetic loop antennas:

The models of the AMA Loop Antennas

Originally there was a large selection ofAMA loops on offer. After taking over of the construction documents and the rights to the name, we have to gain experience in which models are in most demand, which models pose special challenges for production etc. So we will start with a rather small selection of antennas, which will be extended after a while.


Käferlein AMA Magnetic Loops
AMA21DH AMA31D AMA41 AMA45D AMA42DH AMA85 AMA87 AMA82 AMA84DH AMA163 AMA164
Diameter 0.8 0.8 0.8 1.3 1.7 0.8 1.3 1.7 3.4 1.7 3.4 m
Max. Power 500 250 100 250 500 100 100 100 500 100 100 W
Bands 160 m 160 160
80 m 80 80 80 80 80 80
40 m 40 40 40 40 40 40 40 40 40
30 m 30 30 30 30 30 30 30 30
20 m 20 20 20 20 20 20 20 20
17 m 17 17 17 17 17 17
15 m 15 15 15 15 15
12 m 12 12 12
10 m 10 10 10
Gain
[1]
160 m -10.9 -5.8 dBi
80 m -13.5 -6.9 -4.7 0.2 -4.8 0.2 dBi
40 m -4.9 -1.0 0.4 -4.9 -1.0 0.4 1.6 0.4 1.6 dBi
30 m -1.3 -1.3 0.8 1.3 -1.3 0.8 1.3 1.3 dBi
20 m 0.6 0.6 0.6 1.4 1.6 0.6 1.4 1.6 dBi
17 m 1.2 1.2 1.2 1.6 1.2 1.6 dBi
15 m 1.4 1.4 1.4 1.7 1.4 dBi
12 m 1.6 1.6 1.6 dBi
10 m 1.7 1.7 1.7 dBi
Efficiency
[1]
160 m 2 17 %
80 m 2 10 22 69 22 69 %
40 m 21 53 72 21 53 72 95 72 95 %
30 m 49 49 79 90 49 79 90 89 %
20 m 76 76 76 92 96 76 92 96 %
17 m 88 88 88 96 88 96 %
15 m 92 92 92 97 92 %
12 m 95 95 95 %
10 m 97 97 97 %
Bandwidth
(VSWR 2:1) [2]
160 m 3 4 kHz
80 m 4 3 4 9 4 9 kHz
40 m 7 11 12 10 11 12 28 15 28 kHz
30 m 11 11 22 26 17 23 26 33 kHz
20 m 20 20 24 41 38 33 46 45 kHz
17 m 32 32 36 65 49 75 kHz
15 m 42 42 53 87 68 kHz
12 m 62 62 80 kHz
10 m 80 80 97 kHz
Order No. 11255.21DH 11255.31D 11255.41 11255.45 11255.42DH 11255.85 11255.87 11255.82 11255.84DH 11255.163 11255.164

http://www.darc.de/fileadmin/_processed_/c/3/csm_kontrolleinheit_der_ama_7dddc036ca.jpg[1]: Theoretical values by Ch. Käferlein DK5CZ, based on Magnetic Loop calculations DL2FA
[2]: empirical mean value

 

 

 

For operation of the AMA loop antennas a DC voltage of 13.5V, max. 250mA is required, a supply cable is included in the shipment, but no power supply. Further a two wire cntrol cable is required, a wire gauge of 0.75mm² is sufficient. Unfortunately we do not offer such a cable at the moment.

 

AMA loop-antennas are manufactured after order. The current delivery time can be found in the listing below.
Order No.
11255.21DH AMA21 Not in stock, ordered only on customer request, delay at c. 25 days. 1280.00
11255.31D AMA31D Not in stock, ordered only on customer request, delay at c. 25 days. 1090.00
11255.41 AMA41 Not in stock, back in 25 days 1090.00
11255.45D AMA45 Not in stock, ordered only on customer request, delay at c. 25 days. 1290.00
11255.42DH AMA42DH Not in stock, ordered only on customer request, delay at c. 25 days. 1490.00
11255.85 AMA85 Not in stock, ordered only on customer request, delay at c. 25 days. 1250.00
11255.87 AMA87 In stock, shipped in 1 or two days. 1270.00
11255.82 AMA82 Not in stock, ordered only on customer request, delay at c. 25 days. 1430.00
11255.84DH AMA84DH Not in stock, ordered only on customer request, delay at c. 25 days. 1850.00
11255.163 AMA163 Not in stock, ordered only on customer request, delay at c. 25 days. 1690.00
11255.164 AMA164 Not in stock, ordered only on customer request, delay at c. 25 days. 1750.00
11255.CONTRO AMA Loop Controller only In stock, shipped in 1 or two days. 149.00

 

Download: AMA assembly instructions and manual (PDF, DE, 530KB)
Download: AMA brochure (PDF, DE, 1.8MB)

 

Double wire control cable

Double wire control cable, 0.75mm² cross section, black PVC coating. Suitable for the control of magnetic loops that require only two wires (AMA Käferlein Loops or similar).

Order No.
40059.25 25m Double wire control cable, 0.75mm² cross section, black 15.00 In stock, shipped in 1 or two days. 15.00
40059.50 50m Double wire control cable, 0.75mm² cross section, black 28.00 In stock, shipped in 1 or two days. 28.00

Alle prijzen zijn inclusief BTW., maar exclusief verzendkosten.
Tussentijdse prijswijzigingen en typefouten voorbehouden.
Fabrikanten kunnen specificaties en uitvoeringen wijzigen.