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How to Build a UHF Antenna Amplifier

If you are located in a remote TV reception area and must rely on an antenna system/relay transmitter, a UHF antenna booster can provide better reception in the 499-850 MHz range. This circuit has only a single transistor, but you can expect a 10 to 15 DB gain in amplification. Mount it with your antenna above the roof line to avoid cable noise, and run DC power located at your TV up the cable to the booster.

Things You'll Need

Shielded metal box
3 male jacks 75 ohm coax
2 female jacks 75 ohm coax
Long line 75 ohm coax (roof to TV)
P1 5K potentiometer
R1 470 ohm resistor
R2 2.2K resistor
R3 1 K resistor
C1 10 uF 35 V
C2 0.001
C3, C4 .01
C5, C6, C7, C8 10 p
L1, L2 aircore 2 turns 0.5mm 3mm (coil diameter)
L3, L4 10 uH HF choke or 0.2mm 10 turns in ferrite core
T1 2SC3358 Transistor with mounting socket
POWER SUPPLY PARTS
100 pF capacitor
0.01 capacitor
50 to 100 uH inductor or RF choke
soldering gun or iron
solder
needle nose pliers
wire cutters
scewdrivers

Instructions

- 1
  Make copies of schematics and parts placement for amplifier and power supply. (See References) Note the remote power supply using the coax as a conductor for 12 V located at the TV. Familiarise yourself with the plans and clear an area of your workbench for tools and components. Gather components from the "Things You'll Need" list. Many items are common so check your junk box or friends for items. Contact your local electronic supply house and buy or order missing items. Find a weatherproof box suitable for holding and mounting components, i.e., exterior coax jacks and potentiometer.
- 2
  Build the circuit around the mounted potentiometer P1 and coax connectors. Be sure to add a grounded metal shield around the transistor and coils indicated on the schematic. This section can be built on the output side of the metal box. A printed circuit is not necessary due to the small number of components. However, add chassis mounted connecting terminals as necessary.
- 3
  Wind coils L1,L2 per instructions on schematic. L3, and l4 can be made or purchased as 10 uH UHF chokes. For detailed air core inductor design and building information, see references. L1, and L2 can be connected directly to the metal box ground. Locate connecting terminals at convenient locations. Solder all components in place and cut off excess wire.
- 4
  Solder male coax connectors on both ends of the long line coax cable. Add the 12 V power supply at the TV and isolate with capacitors and choke. These components should be at end of the coax cable going to the TV. Split the coax cable and solder in place. Cover with electrical tape. The amplified signal comes down the cable, and the power to run the amplifier goes up the cable.
- 5
  The antenna booster must be as close to the antenna as possible. Mount it on the antenna close to its output. You want to amplify this signal from the antenna and not stray noise picked up by the long line of incoming cable. Your real TV signals will be at least 15 DB above the noise and background level. Adjust P1 for best reception, which should be at a working current of 5-15 mA.

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