The MLA-S (MRT) is operable on amateur radio bands from 80m to10m with a maximum power rating of 50W.


549.00 €


in stock


The MLA-S (Multiband Remote Tuning) is a newer variant of the well-known MLA-S (MMT) model (Multiband Manual Tuning), which with regard to the usability from 80m to 10m with 40W output power belongs to one of the most popular commercially produced magnetic loop antennas in this price category. The MLA-S (MRT) elevates the utility of the MLA-S (MMT) by being designed for remote tuning (RT), and by increasing the power sizing up to 50W. The method of installation is by means of a three-legged tripod with 1/4" universal fitting. Tripod is not included.

Bands and power

The MLA-S (MRT) is operable on amateur radio bands from 80m to10m with a maximum power rating of 50W. When transmitting with this maximum usable power, it is not advisable to sit at the wake-up antenna less than 5m away. The antenna is not safe for operators with pacemakers! The switching of the band segments is done by two external JUMPers according to the table below.

Red - 80m and 60m
Blue - 40m and 30m
without jumper 30m to 10m

Tuning within the segments is provided by a DC motor, which is connected to the CB4M MINI driver box via an audio cable with 3.5mm JACK connectors. Because the variable capacitor used has stops (it only rotates 180 degrees), standard use of this type of capacitor tends to be more complicated and requires the use of limit switches and simpler electronics. The innovative MLA-S (MRT) solution significantly simplifies the use of a variable capacitor that only rotates 180 degrees, without these otherwise necessary complications. Remote tuning is provided by the CB4M MINI controller electronics. Unlike its use with the MLA-S (portable RT) antenna, the arrows on the CB4M MINI controller can be designated as FRQ UP and FRQ DWN. A more detailed description of the controller is below. The appearance of the MLA-S (MRT) and the CB4M MINI controller can be seen in Figures 1 and 2. The CB4M MINI controller is included in the package.


CB4M MINI is a CONTROL BOX for remote tuning of magnetic loop antennas. It extends the range of previously used CB4M, CB4M DUO, CB4M UNI controllers, which were created gradually with the continuing development and expansion of the type range of magnetic loop antennas produced by BTV and LOOPER SYSTEMS.

The CB4M MINI is the simplest of the range of drivers. Because it uses knowledge accumulated over several years, it performs the remote MLA tuning function very well even without the PWM control previously used. Unlike the CB4M, the CB4M DUO has an integrated internal 9V replaceable battery to power the controller electronics and to operate the DC motor that turns the magnetic loop antenna capacitor. The battery power supply significantly reduces interference (background noise) caused by poor quality mains adapters.

Unlike the CB4M and CB4M DUO, the CB4M MINI is not equipped with a DC turnout (bias -T). Therefore, an additional cable is required to control/tuning the MLA-S (MRT). A standard JACK/JACK (male) audio cable is used to connect the MLA-S (MRT) to the CB4M MINI, supplemented with a 5m or even 10m extension cable as required. Both the MLA-S (MRT) and the CB4M MINI are equipped with a stereo (female) 3.5mm JACK connector. The 3.5m cable and 9V battery are included.

CB4M MINI control - MLA-S (MRT) tuning

For remote tuning of the MLA-S (MRT), the CB4M MINI is equipped with three buttons on the top panel of the cabinet. Two buttons (triangles) provide FRQ UP/FRQ DWN functions, the third button (circle) switches the tuning speed - coarse/soft. This function of the CB4M MINI is solved by changing the voltage for the DC motor. In the fast tuning mode, the rotation speed of the DC motor can be factory set using the internal R-trimmer. In fine tuning mode the voltage/speed is fix. The two outermost LEDs on the top panel indicate FRQ UP/FRQ DWN tuning, the middle LED indicates the tuning speed in color. Green - slow mode, orange - fast mode. The CB4M MINI controller is shown in Figure 1. Figure 2 is a detail of the MLA-S (MRT).

Technical parameters

  • Frequency range:3,5 to 28 MHz
  • Input impedance:50 Ohm
  • Typical Q:up to 250
  • Maximum usable power:50 W
  • Best achiavable SWR:1:1 max 1:1,2
  • Input connector:BNC
  • Dimensions:0,85 x 0,17 x 0,90 m
  • Weight:1,6 kg
  • Loop Diameter:850 mm
  • Antenna tuning indicator:yes