RX Loop Design

Our goal (PA0FRI / PD0EEA) was to make an Active Loop amplifier, with a limited number of parts. An amplifier that performs well despite its simplicity. After two years and three new PCB designs, we have come to this final design.

Latest PreAmp developments

            for closed magnetic Loops

 Check this Page date for the latest updates... Latest update was: 13.4.2023

It seems that there are people who, due to the wide range of designs and modifications on the PA0FRI site, no longer know which Loop Amplifier is the right one. Frits has given his own interpretation to the resistance values.

In the diagram below you can see the simplicity of the resistor values indicated by me with the same operation of the Loop Amplifier.

The Powerboard was equipped with an LM317, but due to problems with this voltage regulator, I adapted it for a 7809 version. It must be mounted in reverse. A resistor also disappears and there is a Jumper instead of a capacitor.. Look below..

It is possible to use the cheaper SS9018 transistor instead of the 2N5109. This has other B, E, C connections. see the Datasheet for the right connection.

The RF Choke of 1000uH (1mH) must be at least 100mA. If the value is too light, winding closure will occur, causing the gain to decrease.

The White core can be changed for FT 50 - 43 With 2 x 10 Bifilar windings. Connection is the same.

For placement the Pig Nose core between Loop and Amp, look the Picture below. This modification is not absolutely necessary but an option for the 1.20 Loop.

                            PA0RFI Latest Loop Amp. Schematic

The 2K2 potentiometer that was added last can (with some technical insight) be mounted on the existing / Latest PCB. The two base to ground resistances then disappear.


      My Latest Mods for the 2N5109 / SS9018 Magnetic Loop Amplifier

I've made the resistor value much easier. The reception quality is still the same

The BN-43-302 Core ( Between Amp and Loop connection is an option, for better reception between 10 - 30 MHz. Reception is flat until 35 MHz. This is calculated for 1.20 meter Loops.

If you have any questions... >> Please let me know <<<   hollandshortwave@gmail.com


      My latest (Magnetic Loop) Amplifier with Single Wide range BFG 135a Power transistor

Latest PCB, Single BFG135a in stripline configuration. 

This single PreAmp is build with the BFG 135a, a Wide band (5 GHz) Power Transistor. Gain: 27DB from 0.02 - 30 MHz, (18DB 250 MHz) Current: 80 mA/12 Volt. With a 7809 Volt stabilizer. Noise: 1.84DB. Push Pull Loop input by Two transformers and current Balun. Heatsink is created by metalized PCB Pads and SMA 50 Ohms output connector. 

           This PCB is tested and works as described. 

Loop input PCB is build by Two Push Pull transformers, with current Balun for asymmetrical 50 Ohms input to the BFG 135a. Result is a flatness gain from 0.02 to 30+ MHz 

Below the last Push Pull PCB created last year by PA0FRI / PD0EEA. Sold more than 150 Around the Globe from USA / New Zealand etc..

Both PCBs with 2N5109 in Puss Pull. Below the amp with the FT 50-43 core 2 x 10 windings bifilaire.

 PCB board for Symmetrical / Asymmetrical connection. Flat response from 0.02 - 30+ MHz.

Symmetrical Loop input PCB for connecting to a separate 50 Ohm PreAmp.

On the back side (Left) for optional Low Pass/ Band Pass filter. On the right side Pad for the 7809 Stabilizer. In the middle, Collector Cooling Pad BFG135a

On the back of the PCB single Amp, there is a possibility to create a Low / Band Pass section.

BFG 135a Schematic... This 1 Watt 5 GHz Power transistor is overload resistant and does not suffer from IMD or other by-products due to the setting.... And 1.5 dB noise level at 100 MHz.

          For more information about these PCBs, write me by mail: hollandshortwave@gmail.com