Thursday, July 3, 2014


      QRP transceiver from VU2ESE. Its a semi software defined radio for general coverage HF which uses Si570 XO from silicon labs as local oscillator controlled by Arduino controller ATMEGA328P. For more details regarding construction, features and circuit designs feel free to click this resourceful link.

      This project is in R&D stage and still you can find a crowd of audience discussing its performance which clearly states its the best of its kind. Fore those serious critical examiners there is a forum for discussion about ongoing updates and modifications regarding core issues Freelists.

MINIMA Schematic Diagram

   Just received the PCB set from VU3SXT and i cant resist my curiosity to get started.Here is the PCB in my lab just started smoking some solder.

Partially assembled components Day 1

Partially assembled components Day 2

 Amplifier section completed Day 3


      Audio amplifier and preamplifier tested... so far so good. Power amplifier alone gave weak output signal from mp3 player. Slight modifications were made on the feedback resistance values on power amplifier circuit from 22 Ohm to 10 Ohm and the emitter resistance of the Q16 from 100 Ohm to 10 Ohm to get maximum output. But on addition of preamplifier stage in the chain the amplifier output level was good without any modification with the same test signal.

Mixer stage completed Day 4

      The story begins with winding 8 turns of trifilar wire on FT37-43 toroid. A trifilar wire of length 12cm was measured including 1cm pigtails. An inductance of 43.2xx uH was measured per coils of transformer. The JFET's used are BFW11. Test was conducted before and after setting JFET bias voltages by injecting 20MHz from BFO to mixer as IF signal and signal generator output as LO was injected to the mixer with frequencies 27 MHz and 34 MHz for 40 M and 20 M test respectively. The plots showing test results are shown below.

Note: All frequency in plot have an offset of 24MHz. The frequency products other than the required frequencies appear due to many other reasons and is not from the output of the mixer and can be considered as noise.

      The video below shows the changes in the mixer product when the JFET bias voltage is varied. The test is conducted with LO as 34 MHz and IF 20MHz. Also the frequency offset of 24 MHz is applicable on the plot.

Crystal Ladder Filter completed Day 4

      Crystal frequency was tested for each one using a non-super calibrated frequency meter. Eight lucky crystals with matched frequency were chosen for the filter. The test results of the filter is given in the video with limited test equipments i used. Here also the frequency offset of 24 MHz is applicable for the plot.


First QSO's with MINIMA Day 5

      This is my test setup, the external amplifier wired using LM386 is from a crashed BITX20 Board. The VFO is DDS VFO tuned to 40m and LPF is skipped.

      You can hear few QSO's from my MINIMA. Unfortunately they are captured using 2.5 Mpx stone-age mobile but you can still hear and see my setup with the stone age resolution :) ...

1 comment:

  1. It is good to see the foots of work in progress, we would like to have minute details of how you made it. De ve3inj. Thanks.