Cross Country Wireless HF Antenna Isolator
Cross Country Wireless manufacture a HF Antenna Isolator for HF and 50 MHz use.
It is a galvanic isolation transformer isolating the mains earth or ground at the station from the antenna or tower earth or ground. This is necessary in areas where PME (protective multiple earthing) is used. Isolating the antenna earth or ground from the incoming mains supply is recommended for electrical safety in case the incoming mains earth or ground has a fault and any mains electricity fault current tries to flow along the co-axial cable to the antenna earth or ground. As the co-ax cable is not designed to handle the high fault current there is an electric shock and fire risk in this situation.
It has two outputs, one a 1:1 transformer impedance ratio for 50 ohm operation and the other a 4:1 transformer impedance ratio for use with non-resonant vertical HF antennas such as the 50 feet, 43 feet or 31 feet versions.
The HF Antenna Isolator also protects the station equipment from static electricity charges on the antenna. An additional terminal is provided to safely discharge an isolated antenna system to ground via a 1 M ohm resistor and 20 kA gas discharge tube.
A low noise antenna design using loop counterpoises isolated from ground was featured in the October 2020 issue of RSGB RadCom. The article can be downloaded here.
The connections looking at the label clockwise from the SO239 connector are: 1:1 (50 ohm) output, 4:1 (200 ohm) output, loop counterpoise connection or ground and ground terminal if using isolated loop counterpoises.
Frequency range: 1.8 to 50 MHz
Input impedance: 50 ohms
Output impedance: 50 and 200 ohms
RF power rating: 500 W maximum
Galvanic isolation between input and output
Each unit proof tested for 1000 V electrical isolation between input and output
Low pass filter >40 dB above 350 MHz
Connector: SO239 female
Additional terminal for 20 kA gas discharge tube and 1 M ohm resistor for safety connection to an isolated antenna
Tough polycarbonate case with stainless steel terminals suitable for outdoor mounting if connectors are waterproofed
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