EME232 HF Active Whip Antenna
The HF Active Whip Antenna has been designed to be easy to construct and install, and covers a wide frequency range from 100kHz to 80MHz. It is particularly useful for those that have antenna restrictions or limited space to install a full size receive only antenna, and can be used in antenna arrays for noise cancellation or beam forming. The design incorporates static and lightning protection, and has a broadband 50ohm output ( 75ohm optional ) output impedance suitable for driving most receivers. A J310 FET is used as the active device, and along with a complementary push pull output buffer producing high output second and third order figures reducing the possibility of inter modulation on the received signals. The design incorporates power supply decoupling so that power can be fed to the Active circuit via the coaxial cable.
The recommended Antenna is a 1.2 metre long stainless steel VHF whip antenna mounted onto a truck mirror mount. and but anything from 1 to 1.5 metres long is suitable including most telescopic car radio antennas. The Antenna is physically short for the low frequency HF bands, and will appear as a small 22pF capacitor to ground on the active input circuit. Antennas longer than around 1.8 metres, may increase the possibility of strong signals overloading the active circuit causing inter modulation. The active circuit and whip antenna is mounted onto a 2 metre long 1 inch 25.4mm diameter square or round aluminium tube. The active circuit can then be easily mounted onto the same tube, and then short connection wires are connected from the antenna to the active circuit. At least 3 ground radials 3 metres long each are laid along the ground for the best performance.
Testing indicated that receive signals below 10MHz may require an 10dB gain amplifier on the receiver input to increase signals to a more comfortable level due to the short antenna length. Some modern receivers incorporate preamplifiers that can simply be switched on, on the lower bands.
In very strong AM broadcast areas, some lower quality receivers without good filtering may suffer from inter modulation from strong signal overload. A suitable 1.8MHz high pass filter should be fitted at the receiver input to reduce broadcast band signal levels.
1/ There are no current changes for this product.
The images below show both sides of the board. The construction is quite easy due to the use of larger SMD components and only one transformer that needs to the wound. Click the pictures for a more detaild view.
1/ There are no changes to this product.