The BC-121.5 DF Antenna
The BC-121.5 Antenna is a 3-element Yagi beam antenna. It is specifically designed to be a hand held, fold up, portable radio direction finding antenna for use on 121.5 MHz. It is designed to be compatible with a wide range of equipment, including both the older and newer models of the L-Per, the MK-4 Sniffer (shown below), and any hand held receivers (receivers may require an antennuator).
Designed in consultation with industry experts including Joe Moell, K0OV, author of “Radio Direction Finding Simplified”, and Bob Thornburg, a noted RF engineer and transmitter hunter, we utilize the EZNEC 4.0 antenna program to model and optimize the antenna then tune it using an antenna analyzer. The antenna design was tested at NASA’s Jet Propulsion Laboratory in Pasadena, California to verify antenna characteristics and ensure design specifications were met.
Technical and Design Requirements
Our technical design specifications for each antenna are strictly adhered to*. Each antenna must:
- Fold up neatly for storage
- Have a good front-to-back ratio
- Have no side lobes at resonance
- Have good forward gain
- Specifically resonant at 121.5 MHz
- Have a standing wave ratio (SWR) of less than 1:1.2 @121.5 MHz
- An X-factor of less than 3
- Have an impedance of 50 ohms + or – 2 ohms @121.5 MHz.
- Have a balanced feed point
- Have good adjacent frequency rejection.
*Since all our products are custom-made to your exact specifications, please allow a few days for us to design and build your antenna.