Advertisement
fm antenna amplifier circuit schematic

FM Antenna Amplifier Circuit

Use this fm antenna amplifier in areas where the signal reception of FM stations is too bad.
This circuit is just the right thing to do it. It is designed in such a way that the supply current powering it flows through coaxial cable.

With this technique, an extra cable to power the fm antenna amplifier is unnecessary. The RF signal and the DC current supplying the amplifier use the cable simultaneously. Check another FM antenna booster circuit diagram.

FM antenna amplifier circuit schematic

fm antenna amplifier circuit schematic

The RF signal is however prevented by LC filters from flowing into the power supply. The amplifier works with either 50 ohm or 75 ohm antenna. It has a gain of 25 … 30 dB. MOSFETs are used to avoid the problem of crossmodulation or intermodulation. The circuit is divided into two parts. The first part is the active aplifier circuit which is normally installed very near the antenna. The second part is the power supply circuit which supplies current to the amplifier through the coax cable.

After the fm antenna amplifier circuit is constructed, the power supply should be connected to it. You must then test the DC voltage in the cable. This must be between 15.5 and 36.6 volts. Then test the voltage between T5 collector and ground while adjusting the supply voltage. It must move from 3 to 24 volts. The emitter of T2 should be approx. 11.4 volts. If the voltage at R4 is between 0.7 and 2 volts, then the MOSFET is functioning properly.

Important points to follow in constructing the circuit:
– The circuit must be constructed in a double sided PCB
– T1 must be shielded
– The source terminal of T1 must be soldered directly into the copper plate.
– C4 terminals must be as short as possible
– Coil terminals must be as short as possible
– The antenna must be conneted directly to L1
– T2 must be heatsinked

Power supply for the FM antenna amplifier
fm antenna amplifier supply
FM antenna amplifier active components and coils values

  • T1 = 3N225, 3SK85, 3SK87
  • T2 = 2SD781, 2SD1177, 2SD1684, MJE243, MJE244
  • T3 = 2SA970, 2SA1136, 2SA1137
  • T4, T5 = 2SC3622, 2SC3234, 2SC3248
  • L1 = 9 turns 0.7mm, tap at 1st turn from the ground
  • L2 = 6/3 turns (A&B) 0.5mm on Amidon T37-12
  • L3 = 9 turns 0.7mm, tap at 3rd turn from the ground

9 Comments

Join the conversation!

Error! Please fill all fields.
  • relab

    Hi,
    interesting circuit! Can I use this antenna amplifier circuit for amplifieng signals from my signal generator?
    I need a higher voltage like 70V and about 1 amp.
    Many thanks!
    Greetings
    Sebastian

  • Gayan 4s6ggs

    I modify it to receive and amplify 2m 145mhz signals in the range

  • Aseem Kumar Chawla

    I have a VHF TV Booster bought when we used to watch terrestrial DD TV transmissions. Can I modify it to receive and amplify FM signals in the range 88.7 -108 MHz and feed it to my FM Receiver?

    • shnaj

      Yes it possible simply connect the wire into the fm radio antenna and adjust the gain control

  • adrian.engineers

    is-it like vhf tv rf–in-booster????

  • Vishwaeshakumaaran

    You have to raise the antenna at least 10mts above the ground level to isolate it from the ground.Anything above the 10mts is excellent.

  • P.K.SINGH

    is it tested, can i able to received the signal from 150.00 km away fm stations with the help of this circuit for the 87.5 mhz -108.00 mhz and what should be hight of antena and type of antena
    also clear the l6 coil winding detail

  • P.K.SINGH

    can i able to received the signal from 150.00 km away fm stations with the help of this circuit for the 87.5 mhz -108.00 mhz and what should be hight of antena and type of antena

Looking for the latest from TI?