The combination of several products into one makes this product unique and has a wide range of applications. The first thing is the input transformer with switchable ratio - input impedance. This makes it possible to connect this box directly to antennas with impedances around 200, 450 and 800 (to 1200) Ohms.

Jump to

Applications
Block diagram
Examples with antennas
200 Ohm antennas
450 Ohm antennas
800 - 1200 Ohm antennas
Power Supply
Jumpers and settings
Measurements
Universal Terminator
Article
Product details

Applications

Many RX antennas (RX loop, K9AY, Flag etc.) have negative gain, inserting a coaxial cable between the antenna and the amplifier can induce unwanted signals and further attenuate desirable ones - plus depending on common-mode current problems. Therefore, in this device the signal is amplified immediately at the feed point of the antenna.

Surge and RF power protections are inserted before and after the preamplifier. A Low Pass Filter with a break frequency of 11 MHz can be inserted before the preamplifier.

The preamplifier can be powered either directly - via cable gland and internal connector, or via Bias Tee over coax.

feeder box with PL SO-239 connectors

universal terminator

Block diagram

This is a block diagram of Feed Point Preamp. It simply shows the different parts of the preamp. This will give you an idea of what all is included in the box and what you will get.

Examples with antennas

⚠ IMPORTANT NOTE: Please set the appropriate impedance according to the selected antenna! In Feed Point Preamp and possibly also in Universal Terminator. More in Jumpers and settings.

200 Ohm antennas

This Feed Point Preamp with Universal Terminator could be directly used with Single Wire Beverage antenna on ground - BOG

450 Ohm antennas

There are different RX antennas with 450 Ohm like K9AY and Classic Single wire Beverage

Read also our technical article about K9AY

800 - 1200 Ohm antennas

DHDL RX antenna (optimal parameters with 950 Ohm terminator) - read article by AA7JV and OK1RR

Delta RX loop

Flag RX antenna

Pennant RX antenna

Power Supply

Connecting the supply voltage is possible in two ways:
- directly through the cable gland to the connector on the PCB
- via an external Bias Tee over coax

It depends on the location and use of this box. The supply voltage must be DC (ground is negative) in the range of 12 to 15 V.

⚠ IMPORTANT: If you don't use cable gland - insert a piece of cable and seal it. This will prevent moisture and possible insects.

example of directly connection through the cable gland

example of connection via an external Bias Tee over coax

Jumpers and settings

There you can find a description of the Jumper and Trimmer functions. With Jumpers you can change parameters such as input impedance, input LPF, RF limiters and possibly check/set the BIAS current of the transistor.

1. Low Pass Filter 11 MHz

- There are two jumpers - you can switch between wide Band input or Low Pass Filter which cut off frequencies above 11 MHz - see measurements

2. DC power over coax

- This jumper must be shorted when you use Bias Tee and send DC power over coax

3. Current test points

- You can check/set BiAS current at these test points
- Connect 200 mA meter there. Current should be set to 30 to 50 mA @ 13.8 V

4. Antenna Impedance

- Set jumper to the position you need
- This depends on antenna

5. Input RF limiter Impedance

- When the jumper is shorted, the input RF limiter is connected
- Limiter cut RF signals to max. (typ.) + 17 dBm at input

6. Output RF limiter

- When the jumper is shorted, the Output RF limiter is connected
- Limiter cut RF signals to max. (typ.) + 21 dBm at input

1. Bias Current set

- This is 30 turn trimmer
- By this trimmer you can set transistor bias current
- Recommended around 30 to 50 mA @ 13.8 V

2. External DC power

- There is internal screw terminal for DC in
- In the case you do not use Bias Tee and power over the coax, you have to connect DC voltage there to this terminal

3. Variable ATT

- This is 30 turn trimmer
- It is connected at the output of preamplifier and works as a Variable Attenuator
- You can set total gain from nill to around 18 dB

Measurements

These are the gain graphs of the whole box with wide band input and with 11 MHz LPF on

Wide band input (measured with another transformer from 50 to 450 Ohm at input)

Low Pass Filter switched on (Gain is typ. 4 dB at 20m, - 46 dB at 10m)

Universal Terminator

We also offer the Feed Point Preamp in a set with a universal terminator. Universal because you can set 4 different resistance values + add 50 Ohms to each. So up to 8 fixed values in total. The terminator can be permanently loaded with up to 3 W of RF power. Among other things, it includes voltage and current (power) RF protections.

This terminator can be used with both Beverage antennas (classic and BOG), RX loops with impedance around 450 Ohm and RX antenna with impedance p to 1200 Ohm.

Article

ℹ   Read article by AA7JV and OK1RR.