Cross Country Wireless HF Active Antenna
The HF Active Antenna was developed as part of the development work for the Sentinel HF SDR noise measurement receiver and program.
There was a need for an antenna that could be used for accurate RF measurements over a wide range of HF frequencies without being affected by coupling to nearby metallic objects or RF noise from common mode coupling on the feeder and would give long term repeatable results.
If it was an active antenna it also had to be capable of surviving high RF field strengths from HF transmitters operating on the same site and be tolerant of mounting position and supply voltage.
It also had to be built from the highest quality materials to work unattended for years in all weather from arctic to tropical conditions.
It also had to be sensitive enough to receive and measure the RF noise floor at the quietest sites without being overloaded by the strongest broadcast signals in the HF bands.
Finally it had to have two RF outputs so that one could be used for a Sentinel HF SDR noise measurement receiver and the other for another HF receiver for general listening.
This is the result...
Balanced small dipole design using two 0.65m stainless steel elements
Frequency range 100 kHz to 50 MHz
Uses low cost ethernet cable to connect between antenna head and base coupling unit
RF gain equivalent to an isotropic antenna (0 dBi) from 100 kHz to 50 MHz
Antenna amplifier uses balanced FETs and an E-PHEMT high IP3 amplifier
Transformer balanced coupling to ethernet cable for excellent common mode rejection
RF overload protection allows use in close proximity to transmitting antennas without damage
Outdoor unit has polycarbonate enclosure with brass and stainless steel fittings
20m of outdoor ethernet cable terminated with RJ-45 connectors included with each antenna
Two RF outputs on the antenna base unit
DC supply requirements are 12V at 120 mA
The HF Active Antenna Operating Manual can be downloaded here .
YouTube video of early prototype HF Active Antenna
The green LED is Power, the red LED is Antenna connected.
A quick covert installation in a tree. Almost invisible!
Close up of "temporary" installation.
Contact Chris Moulding, G4HYG via Email address hidden from spambots for more details.
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