Monday, October 8, 2018

Homebrew 5 Watts 40m CW Transceiver Using TIA Amplifiers. Si5351 Based Superhetrodyne Receiver

All design ideas from the EMRFD book. Thanks to W7ZOI, KK7B, W7PUA. And i'm blessed to get this book in India at a second hand book seller. I told him to reserve any radio related books, one fine eve he called me about this book. I also bought ARRL 2011 book. If i'm not using the design concept from this book, then its a shame on having the book. So, here is my QRP Project..

1st design requirement is, front facing 4" speaker. No compromise.

I wanted this to be a self powered, no need to search for DC adapter. The transformer salvaged from old HI-FI cassette player. 15V 2A. I used 12V regulated power supply for TIA chain. Rest using unregulated 17V. 

Close up view

From right >> RX/TX antenna relay >> 40m BPf >> 1st TIA amp >> VFO diode ring mixer >>10MHz ladder filter >> 2nd TIA amp >> 10MHz BFO >> 2nd diode ring mixer >> 2N2222 preamp >> audio power amp >
ULN2003 for all relay switching

Transmitter stage. >> 2N2222 >> BD139 >> 2SC1971 >> 5th order LPF . 2SC1971 gives spurr free 5 watts clean output with 17V 2A. I connect SI5351 clock output directly to 2N2222. All are TV balun cores. Cause thats what i have.

Side tone oscillator , Power supply and audio amplifier close up view

This is my own SI5351 clock generator board using ATMega8. ( I Hate arduino. ). I'm using C language in this project, but assembly version is in progress. You can find details about this PCB on this blog, look for SI5351 DDS board..

The speaker is from old National Panasonic cassette player. Excellent audio quality.

Etched TIA Amp board, i made about ten PCBs for future uses. Around 1" x 1" approx

Initial layout. Modular PCB system makes very easy to assemble and troubleshoot.

Sunday, July 1, 2018

Si5351 DDS Clock Generator Using ATtiny13 Microcontroller with assembly language


This is my project to demonstrate the simplicity of assembly language program. Usually we need lot of program size when we use Arduino compilers and its library. I'm much worried about the program size and coding efficiency. So i wanted to try my skill to make assembly language code to interface Si5351 DDS. After the introduction of mobile phones we lost our memory capacity to store the phone numbers in our brain. Similarly Arduino is spoiling our programming skills. It of-course opened up the creativity on hardware side, but on the software side most of the peoples copy-paste. The first place to look for Arduino code is google. Most of us just copy somebody's library and use it. Arduino made everybody to hesitate to study the datasheet and follow the instruction. I'm not an anti-arduino man, but i want to blow the whistle.

The challenge in this project is 1kB or less program size to interface Si5351 chip. I took the challenge myself. In arduino 1kB is just enough to blink LED with some sequence. Thats the beauty of Arduino ..LOL

 Project Specification:

  • Use the Si5351 as variable frequency oscillator to cover CW range
    • Ex : 7000 to 7050 KHz
    •        10100 to 10150 KHz
    •        14000 to 14050 KHz 
    •          3500 to 3550 KHz etc...
  • To change the frequency using potentiometer
  • CLK2 as beat frequency oscillator for required frequency
  • Control the VFO or ON/OFF the CLK0 output with morse key
  • 1 digital output for TX/RX relay
  • Operating voltage is 3.3V for ATTiny13 and Si5351

Circuit Diagram  

Source Code :

80m - 3500 to 3550 KHz
40m - 7000 to 7050 KHz
30m - 10100 to 10150 KHz
20m - 14000 to 14050 KHz 

Youtube Video

Wednesday, November 1, 2017

Valve Audio Amplifier

Magnetic Loop Antenna For Transmitting

After the success of my receiving magnetic loop, i wanted to give a try on transmitting loop. It has both good and bad results.

One fine evening my friend OM Prem VU2RPC and myself started fabricating the magnetic loop to transmit on 40meter.

Used 3/4" copper tube used for air conditioner with a length of 9 feet.
Wide spaced variable capacitor 30-300pF salvaged from old valve transmitter
2.5SQm wire for inner loop.
Construction is as simple as possible. Just used 3/4" PVC pipes.
Just maintained the outer loop dia as 3feet, and inner loop 0.5feet.

We had about 10 contacts within 15 mins, it was sunday. The tough part is to keep the SWR.
The loop is very narrow bandwidth, even 10KHz change is frequency will affect the SWR to 3:1. Really bad, so maintain power level not more than 50 watts.
The RF from the antenna was also very severe, we can feel the radiation.

Result :
The overall result is,
It is definitely compromised antenna for receiving. There is no doubt, we had no noise pick up, and very good gain also.

For transmitting it not a good antenna. Unless we want to use just for only one frequency, like beacon. Because the bandwidth is too narrow. We have to adjust the variable capacitor for every change on frequency.

Magnetic Loop for Shortwave Receiving

DRM AIR +6100 KHz Shortwave receiving Magnetic loop antenna for 80m to 20m band

This is my trial during year 2015 to receive All India Radio DRM signal from Delhi, India. I'm located south India which is 3600Km far. The actual DRM on 6100KHz is transmit to cover 80Km surrounding Delhi. I made a simple Magnetic loop to get signal from that far. It was a huge seccess. Since i'm using magnetic loop the noise level was very low, and i can null alomost to zero. Below you can find the pictures of my AIR DRM 6100KHz.

I used old Oats container filled with sand on it as a post support. 3/4" PVC pipe, inside is a house electric wiring wire (3-20swg wire). Its about 3feet diameter. The outer loop is connected with a 365pF broadcast set variable capacitor. Inner loop is 1/2 feet dia. I used the same wire.

The radio Redsun (Kaito) RP-2100 comes with a IF out. I made a small converter to convert the RF to AF. Its inside the small black color box.

Saturday, January 7, 2017

VU3XVR Software Defined Radio SDR Using Si5351 DDS VFO and ATMega8 Microcontroller

This is a demonstration on Software Defined Radio Using Si5351 DDS VFO. Original designer is Burkard Kainka, Author of Elektor  SDR-2007. I Just modified VFO by using my own Si5351 based VFO, For more details please chek my blog vu3xvr dot blogspot dot in

Specification :

Frequency Range : 3 to 30 MHz
Mode  : AM - SSB - CW - DRM
Hardware Used :
Software Used : SDRadio by I2PHD available from this website

Thursday, January 5, 2017

VU3XVR Si5351 DDS VFO to Use BITX40

Click here for the video demo of sending CW using BITX (real carrier !!! not modified tone)