This is very simply preamplifier BOX with 2N5109 transistor based on W7IUV design. You can use it as high IP preamplifier for RX antennas (beverage, DHDL, flag etc). Gain is up to 18dB and there is also build in variable ATT. You can easy set the gain as high as you need! As well you can set right transistor bias with multi turn potentiometer. Two relays offer bypass switching if there is no power supply voltage. You can use external power supply connected to the box or the bias tee box for power over the coax.

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Applications
Parameters
Schematic
PCB
Settings
Power over Coax cable
KIT Assembling
Part list
Transformers
Bias Tee BOX
Article
Product details

Applications

- High IP RX preamplifier - RX antennas
- Buffer amplifier
- Driver amplifier

version with PL SO-239 connectors

version with F connectors

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

Schematic

PCB

Settings

Variable Attenuator and RF protections

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

Transistor Bias current:

disconnect jumper JP1
connect mA meter there (200 mA scale is fina)
connect supply voltage you want - from 12 to 15 V
turn the resistor trimmer R4 (BIAS) and set bias current you want - it should be from 60 to 85 mA - depends on application
than connect jumper short back again

Power over coax cable

Short jumper to enable power preamp over coax - with DC voltage.
If you use external power supply to internal DC connector, ⚠ PLEASE DISCONNECT jumper JP4 - Coax PS

KIT Assembling

version with PL SO-239 connectors

version with F connectors

pcb after assembling all the parts

Part list

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

Insert transistor to the radiator and wind output transformer

use screw driver to open radiator a little bit if needed

there is small ferrite core T50-75, wind 5 turns of bifilar wires

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

Bias Tee BOX

You can use Bias Tee BOX for power over coax

example with Bias Tee Box and Bi-Dir beverage

Article

ℹ   Read article RX ANT Switching box on my BLOG.