What is a magnetic loop antenna?
Child and Radio 1925 Franz Fiedler (1885-1956)
I will try to explain in few words how the small magnetic loop antenna works.
1) The magnetic loop antenna is an RF transformer. The primary is the small inner loop that is 1/5 of the size of the main loop.
The secondary is the main loop, and is the actual antenna. This outer conductor is closed by a variable tuning capacitor. The two loops are isolated, with no electrical contact between the inner loop and the outer loop.
2) The magnetic loop antenna is a high “Q” device, so the band width is very narrow. Even minor frequency changes will require the user to retune the antenna, but in exchange the antenna provides superior rejection of unwanted signal reception, the best receiving gain and the lowest SWR in transmit.
3) The magnetic loop antenna can be used for either vertical or horizontal polarization, and the small size makes it easy to alternate between the two.
4) In most radio activities we use the loop in the vertical position -- providing HORIZONTAL polarization -- supported by a small pole. The antenna can be turned freely in both directions to minimize or even completely eliminate man made noise coming from other directions. This position provides a "figure 8" radiation pattern similar to larger dipole antennas.
For condo windows, hotel balconies and other space-limited locations, we use the loop in the horizontal position, which (of course) gives vertical polarization and an omnidirectional radiating pattern.
5) The small magnetic loop works perfectly at low heights. A one meter diameter loop works perfectly one meter above the soil.
6) The small magnetic loop doesn’t need counterpoises, making it ideal for temporary operating locations, or for situations in which there is no room available for counterpoise wires.
Historical references in portable magnetic loop antennas
Balkan’s War in 1942 Alder-shot England, November 1937
PY1AHD COMMERCIAL MAGNETIC LOOP ANTENNAS
AlexLoop SML 7-30 KIT and AlexLoop Walkham
The AlexLoop SML 7-30 small magnetic loop antenna was designed by PY1AHD over seven years of researches and constant improvements.
The field tests confirmed more than 800 QRP DXs and a distance world record registered on the Hall of Fame of the HF Pack group:
AlexLoop SML 7-30 Small Magnetic Loop Antenna Features
Tune in 5 seconds any frequency comprehended
between 6.95 MHz to 29.7 MHz
QSY from a band to another band just on a pair of seconds
The Ultimate Solution for Antenna Restricted Hams
Window Mounted AlexLoop SML 7-30 Magnetic Loop Antenna
AlexLoop SML 7-30 Portable Operation
Enjoy the best from HF pedestrian mobile operation
Follow this simple steps for HF plug and play operation
1) Leave the Velcro that accommodates the cable to the antenna.
2) Connect the cable to the RF output and turn on the transceiver.
3) Hold the antenna and tune with your thumb.
There is no other HF portable antenna as efficient as the
AlexLoop SML 7-30 considering its small size and weight.
AlexLoop Walkham Small Magnetic Loop
The AlexLoop Walkham Small Magnetic Loop antenna goes on a small cushioned bag divided in 3 small 15 inches pieces.
1) The 7 to 30 MHZ Tuner
2) The middle joint piece.
3) The exciter loop.
The AlexLoop Walkham Small Magnetic Loop antenna can be quickly mounted and disassembled for easy carrying.
PY1 AHD ALEX (Alexandre Grimberg).