Circuit: VHF FM Antenna Booster

Paired with an effective directional antenna, a high-performance, two-stage antenna amplifier designed for the VHF FM broadcast band can help you receive distant (DX) stations. Take a look at this FM antenna booster design. It can significantly enhance the quality of FM signals that you’ve previously found to be weak and filled with static in your location.
 

FM Antenna Booster Circuit

The easy-to-build design has a few key features: low noise figure (around 1 dB); high gain (up to 40 dB) and low susceptibility to intermodulation products. The designer N. S. Hari Sankar explains the circuit diagram (see nearby) reveals a circuit: “dual-gate MOSFETs in positions T1 and T2. The first of these, T1, is configured mainly for low noise and antenna matching and the second, T2, for high gain. Unusually, the antenna signal is applied to T1 via its source (S) terminal, which is convenient because unlike one of the gates (G1 and G2) it already represents a fairly low impedance. Nonetheless, for impedance matching with the 50 Ω coax cable a tap needs to be used on tuned filter L1/C2.”
 

The PCB

The amplifier is built on the single-sided PCB. The inductors are simple to make. L1, L2 and L3 are wound on a 4.5-mm diameter drill or pencil. L1 then needs to be stretched to a length of around 10 mm. A relatively large resistor is needed to wind choke L4 on. A 0.5-W carbon-film resistor was used. Refer to the complete article and the associated components list for additional details.
 

More About the FM Antenna Booster

The Elektor article (040145) associated with this FM antenna booster project appeared in Elektor February 2005. Elektor Members benefit from the magazine, an Elektor Store discount, and easy access to Elektor’s library, which includes the article and decades of other editions.