AMRAD Active Antenna Project Page

AMRAD members have been trying out various receiving antennas. The active E-Field probe has proven to be simple and effective. An earlier design was tinkered with to improve its performance. The result is the AMRAD Active LF Antenna. Several were built up and it has been put on a set of printed circuit boards. A construction appears in the September, 2001 QST. The amplifier transistor is biased up to as high a current level as possible to obtain the best performance in an RF dense urban environment. The result is the heat sink that is made out of a piece of copper water pipe.

K0BRA Active LF antenna assembly

We have posted some additional construction information to this web page to help in the construction.

ARRL has granted permission to post the QST article here. You may also find the QST article on the ARRL website at

To help with gathering parts for your AMRAD Active Antenna project we have put together two parts sheets with more detail on the parts and sources. Print these out as you travel hamfests, local stores, dumpsters and the internet and check off the parts as you find them. We have included a lot of the mechanical parts you will need also. We had originally used a Signal Transformer power transformer since they had confirmed, by phone, that they would accept orders for single transformers. Since then they have changed their policy and now require a $50 minimum order. I had an email from Jon Lerner at Mitchell Electronics saying they would like business from radio amateurs and were quite willing to sell single units. I ordered one and tested it. It had almost half the capacitance and looked to be a good replacement for the Signal unit. After testing it is concluded that the Mitchell design is better for our use. The Power Supply Parts list has been updated to now reflect the transformer from Mitchell.

Amplifier Parts

Power Supply Parts

We have been getting some questions about the whys and hows of the antenna. We have compiled an FAQ. You can download it as an Acrobat document here.

K0BRA Active LF Antenna deployed