Wireless Loop Antenna Amplifier

The Loop Antenna Amplifier contains all the electronics needed for home DIY construction of an active loop (magnetic loop) low noise receiving antenna.

The amplifier consists of two units, a weatherproofed outdoor unit for connection to a suitable loop and a base unit to further amplify the signal and to provide DC power up the coaxial cable to the outdoor unit.

The outdoor unit is housed in a polycarbonate box with stainless steel antenna connections and a BNC socket. The indoor unit is a PCB with two BNC connectors and a USB socket to take 5V from a USB socket on a PC or phone charger.

Like our other active antenna products it has RF overload protection to allow it to be used very close to transmit antennas without damaging the amplifier or the attached receiver.

The loop depends on what the user has available. We have tested it with simple wire loops or deltas, coax loops and an alloy loop made from a bicycle wheel rim. We supply a 3m (10 ft) length of wire as a simple loop to make a first loop for testing.

The photograph on the right shows the prototype with a 1m diameter loop of LDF4-50 coax cable as a test loop.

With a simple wire loop or delta and a small USB powerbank it makes a very compact and portable receiving antenna for holiday listening or covert use.

The latest version can now have the head unit powered directly from receivers with a 5V bias-tee such as the SDRplay receivers or some RTL-SDR dongle receivers with a bias-tee option.

Specifications:

Frequency range: 10 kHz to 30 MHz
Loop amplifier input impedance: 0.3 ohms
Output impedance: 50 ohms
Supply voltage: 5 V from USB socket or charger
Supply current (head and base unit): 112 mA
Supply current (head unit fed with 5V bias-tee): 67 mA
Loop antenna outdoor unit connectors: Two M6 stainless steel threaded studs and BNC female (RF out 50 ohms)
Loop antenna indoor unit connections: BNC female (RF input and DC feed to outdoor unit), BNC female (RF output to receiver), USB B connector (for 5V DC power input)
http://www.crosscountrywireless.net/loop_antenna_amplifier.htm