Magnetic Loop antennas by Ciro Mazzoni

Stealth Loop New

Stealth Loop

The Stealth Loop by Ciro Mazzoni was designed to provide an effective antenna to users with limited space. One goal was to build an antenna which is not instantly recognizable as an antenna. The Stealth Loop covers a frequency range from 6.6 to 29.8 MHz (45 to 10m), the maximum power is 125 W CW. Compared to an ideally mounted fullsize dipole the antenna has about 4 dB less signal gain on 40m, and about 0.3dB less on 10m. The useable bandwith which can be used without retuning is about 5 kHz on 40m, and 25 kHz on 10m. Usually an SWR of 1.3:1 or better is achieved.

The construction of the Stealth loop follows the same principle as the well known 'Baby' and 'Midi' loop antennas by Ciro Mazzoni: One side of the loop is fixed, the other side moves by a stepper motor around a joint. Both halves end in interlocking capacitor plates on the upper side, this forms the tuning capacitor of the magnetic loop. Both sides of the loop areconnected with a very wide, flexible steel band which is connected to the frame with multiple screws for best conductivity and lowest resistance. The circumference of the Stealth loop is approximately 282 cm, only slightly less than that of the Baby loop. The dimension of the loop are 137 x 50 x 26 cm, the weight is approx. 10 kg. The frame of the loop is professionally welded from 60 x 20mm wide aluminium tubes.

Stealth Loop Pattern Stealth Loop Pattern

The directional pattern of the loop is slightly directional at very low elevation angles, and depending on the frequency. At hugher elevation angles the pattern becomes nearly round and without nulls. Overall the pattern is also influence by the position and ground conductivity below the antenna. The loop should be operated only outdoors, not inside a building. The minimum clearance to any solid structures should be around 2m to the sides and above the antenna. Solid structures are walls, roofs, railings etc. The placement of the Stealth is very flexible: you can put it on the floor as well as on the roof of a car, on a balcony or garden desk, everything goes as long as the minimum sideways/top clearance of 2m is achieved.

For operatin you need a two wire control cable besides the coaxial cable. 5m cable with connector are included. In case you need a longer cable you can extend the supplied length or mount the connector to another cable. Included in shipment is the automatic tuning unit (ATU 2.0) incl. accessories. This controller offers the possibility to automatically follow the radio frequency by CAT control. In half-automatic mode the frequency can be entered on a keyboard. The tuning process takes between 4 and 10 seconds, depending on the change of frequency.

Stealth Loop SWR Diagram Stealth Loop SWR Diagram
  • Features Stealth Loop
  • Frequency range 6.6 – 29.8 MHz
  • Max. transmit power 125W continous (FT-8, CW, RTTY)
  • Inconspicious construction
  • Low weight, even suitable for portable operations
  • Automatic Tune Unit included
  • CAT control for Elad, Elecraft, Flex, Icom, Kenwood, Yaesu
  • Included in shipment
  • Stealth Loop
  • ATU 2.0 Conroller
  • 10 keypad (USB)
  • 24V Power Supply
  • Motor cable with connector, 5m
  • Printed Manual (italian, english)
Order No.
11252 Stealth Loop 40-10m 1340.00 € Add to shopping cart New In stock, shipped in 1 or two days.
Info freight charges
Stealth Loop Detail Stealth Loop Detail

Special features of the Baby and Midi Loop Antenna

The loop is made of aluminium. Even the smallest antenna has a 50 mm ( 2 inch) diameter of the tubing. Because of the large surface area there is less loss of gain. Both ends are welded on the socket, no screw connections so no contact resistance.

The tuning capacitor on our loops is not a simple variable capacitor but a big variable plate capacitor of aluminium with an air-dielectric. Both plates are also welded directly to the loop and indestructible on high power! The distance between the plates is 14 mm (ca. 1/2 inch) on the smallest antenna.

A weather resistant actuator opens or closes the loop and thus tunes the plate capacitor (SWR tuning).

The capacitance can be varied by a motor and can be adjusted to the best SWR via a control unit in your shack. In spite of their compact size, the antennas are resonant in a wide frequency-range - do you know of any antenna which has a diameter of just one meter (ca. 38 inch) but a frequency range of 40m ... 10m without gap?? Take this one...

Tuning of the antennas is done with either a manual or an automatic control unit. The control units have a 230V power supply integrated.

Automatic control unit

Loop Controller

The tuning of the antenna is done with an automated control unit. This controller is supplied with a 230V power supply. Operation is handled by a small numeric USB keyboard: Enter the desired frequency, wait a moment, ready. The antenna has tuned automatically and is ready to transmit after a short while. No difficult tuning process, no note taking, no complicated search for lowest SWR. The display shows frequency and SWR for immediate check, some LEDs signal the current state of the controller. The max. power load with the automatic controller is 250W! An english manual is included in shipment.

The new version of the controller, which is shipped since spring 2016 contains a RS-232 interface. This interface allows direct frequency control by certain radios. The frequency information is directly transferred from the radio (Icom, Elecraft, Kenwood, Yaesu) to the controller, the antenna tunes automatically to the current frequency. Further an Ethernet interface will be available later as a hardware option.

The new version of the automatic controller is available separately as well and can be used with older models of the manufacturer. To interface an Icom transceiver, an optional level converter is required.

Download: Loop-Manual 04/2018 (PDF, IT/EN, 56 MB)
Technical Data
Frequency Range 6,6-29.8 3,5-14,5 MHz
Diameter 1,0 2,0 m
Impedance 50 50 Ω
Max. Power 250 250 Watt
Front/Side ratio 25-35 25-35 dB
Inductivity 3 µH
Q 1100 (7 MHz)
Weight 12 20 Kg
Tube diameter 50x2 75 mm
Surface of antenna 0,25 qm
Max. Mast Diameter 76 76 mm
Control unit with LC display Optional Optional
Order No.
11250 Baby Loop incl. autom. control unit V2 1399.00 € Add to shopping cart In stock, shipped in 1 or two days.
11251 Midi Loop incl. autom. control unit V2 1580.00 € Add to shopping cart In stock, shipped in 1 or two days.
11253 Automatic Control Unit V2 649.00 € Add to shopping cart New In stock, shipped in 1 or two days.
11250.X01 Mounting platform for antenna as supplied 99.00 € Add to shopping cart New Not in stock, ordered only on customer request, delay at c. 40 days.
Info freight charges

BABY Loop: 6.6 to 29.8 MHz

11250_f.jpg (13387 Byte)

The smallest and most popular selling loop-antenna. Diameter is only 1m (ca. 38 inch). For this antenna space is not a problem: on the balcony, on the roof. The gapless frequency-range is 6,9 up to 29,7 MHz. It comes ready to use with mast clamp. Please order the control unit separately.

Order No.
11250 Baby-Loop 1399.00 € Add to shopping cart In stock, shipped in 1 or two days.
Info freight charges
swr_baby.gif (2994 Byte)

MIDI Loop: 3.5 to 14.5 MHz

11251_f.jpg (6564 Byte)

Midsize antenna, ideal for 80m up to 20m with continuous covering, manufactured on a stable aluminium reed with a diameter of 75 mm (ca. 3 inch). Loop diameter is 2m (ca. 78 inch), can be mounted without radials, like all loop-antennas.

Order No.
11251 Midi-Loop 1580.00 € Add to shopping cart In stock, shipped in 1 or two days.
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swr_midi.gif (2528 Byte)

MIDI Loop with JW4PUA on Spitsbergen, 1000km north of the polar circle

Controlwire for Loop antennas

The Magnetic Loop antennas with manual tuning require four wire for control, the antennas with the automatic controller require two wires. The smallest cable we offer is a five or a six wire cable. With this cable you could 2x2 wires in parallel for manual tuning, or 2x3 in parallel for automatic tuning. Due to the enlarged diameter very long cable runs are possible.

Order No.
40010.6 Control cable, 6 x 0,75mm2, per meter 1.40 € Add to shopping cart In stock, shipped in 1 or two days.
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