This simply low noise preamp module with 2SC5551 is very useful device. You can use it as high IP preamplifier for RX antennas, buffer amplifier or small driver. Gain is up to 18dB and there is also build in variable ATT. You can easy set gain as high as you need! Amplifier has got low noise - lower than 2 dB up to 50 MHz and around 2.2 dB at 150 MHz. As well you can set right transistor bias with multi turn potentiometer. Two relays offer bypass switching if there is no power supply.

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Applications
Parameters
Schematic
PCB
KIT Assembling
Part list
Transformers
Tunning
Article
Product details

Applications

- High IP, Low Noise RX preamplifier - RX antennas
- Buffer amplifier
- Driver amplifier

Parameters

- Supply voltage 12 to 14 V ⚠ HIGHER SUPPLY VOLTAGE NEEDS COOLING AND RESISTORS TO RELAYS
- Supply current up to 180 mA - include relays current

Gain 10 dB 0.5 MHz to 50 MHz

Gain 15 dB 0.5 MHz to 50 MHz

Gain 18 dB 0.5 MHz to 50 MHz

Bypass 0.5 MHz to 50 MHz

Schematic

PCB

KIT Assembling

pcb after assembling all the parts

Transformers

- There is one FT50-75 ferrite core
- Ferrite has got 5 turns of bifilar winding
- Clean coating from the ends. Place wires in right order like on the pictures
- Check it again :)

⚠ Attention, the picture shows a transformer with 6 turns (version for LW and MW). For HF wind 5 turns.

Cut/fold wires in half

Make bifilar winding - you can use small PVC tube and ACU drill

PLEASE measure start and end of both windings, insert it into the PCB in the right order!

Part list

Tunning

- There is nothing to tune on RF side. It is wide band amplifier.
- You only need to set right TRANSISTOR BIAS current and Gain

disconnect jumper JP1
connect mA meter there (200 mA scale is fine)
connect supply voltage you want - from 12 to 14 V
turn the resistor trimmer R4 (BIAS) and set bias current you want - it should be from 10 to 85 mA - depends on application
then connect jumper short back again

- With the resistor trimmer (ATT-TRIM) you can set amplifier gain as you need

from 0 to about 18 dB
turn the ATT-TRIM (201)

Article

ℹ Read article from W7UIV.