Kaimur-The SI5351 experiment

Pursing my keen interest in Homebrewing, I designed some interesting blocks to help me in my design. I have a few PCBs to share with likeminded homebrewers , details of which are:

This is a Si5351 BoB (Break Out Board) which has its own 3V3 Voltage regulator and I2C level shifter for easy interfacing with 5V microcontroller (Connect it to a PIC/Arduino or maybe even a Raspberry Pi)

Almost compatible with the Chinese AD9850 DDS module available.

Size of the double sided PTH PCB – approx 46mm x 25mm (1790mil x 1030mil)

10pin MMSOP to DIP PCB also available for easy of assembly for the Si5351 chip.

Please see the schematic below:Kaimur-3-SI5351-schematic

The Top Overlay


Bottom Overlay


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After being away from the blog for a few months (several), I have been working on a few projects that will be published here shortly. As a short update, I have reworked on the dorji_Module library (EAGLE). Please rename the extension from .doc to .lbr

I’ve also added a schematic  APRS-1.3_DRAFT

Recommended reading

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Vhf Uhf Low power Transceiver VAULT_PCB_Rev1.0

I chanced upon the Dorji modules, which offered a low cost way to build a small VHF or UHF transceiver. According to the site, the DRA818V is a type of compact wireless voice transceiver module based on RFIC RDA1846 andworks in VHF band. It integrates high speed microcontroller, high performance wireless transceiver IC, high power PA, audio process and squelching circuits. It provides standard UARTinterface which users can easily configure appropriate parameters for different applications.

Inspired by this, I decided to create an Eagle library (DORJI) [Rename the file to .lbr], the schematic is VAULT_Sch_Rev1.0. I’ve created a trial PCB in Eagle (click on the picture for full size). See next post for the updated DORJI Library module.

Please note that the module file is yet to be perfected and is included for completeness. Use of this LBR is at your own risk.

Other links:

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Homebrew Antenna analyseR Project

It’s been a long time since I’ve posted anything new here. Development work is always difficult to do in between a day job. There have been several projects that I have been working on for a long time and this is one which I started off eons ago and never got round to testing and publishing it.HARP-Antenna analyser

First a few details; there are of course several commercial antenna analysers and all doing a pretty good job of it as we can see from the price tag. There are also several good experimental designs and choosing one over the other depends on several factors. For me, one of the key factors is the simplicity and availability of components as also the simplicity of the code engine that drives the calculations.

Design Philosophy
Having already familiarised myself with Microchip devices and having access to good technical inputs always helps. The next is the core frequency generator and here too ready code and design from an early project came in handy (See D-SPiRiT from an earlier post). I decided to split the Digital and Analogue sections into the following areas: Motherboard comprising of the digital sections (PIC18F26K22) and the DDS module [Picture 1]. 2 daughter boards comprising the RF amplifier [Picture 2]  and the Detector [Picture 3] section.

The build
I will skip over the circuit explanation as it’s already been done (See links below), and theory was never my strong point. Circuit Diagram is here: HARP-Antenna Analyser_v1.0

DDS: The module does seem to run warm(hot) and maybe it is best to run the module from a 3v3 supply and add 1K resistors on the 3 signal lines between the PIC and the module. I have not done this in the current design, but maybe I will shortly and report back (don’t hold you breath)!!

RF Amplifier: Built straight out of the circuit, with an introduction of a preset(not shown) after Q3 to vary the signal level (I’m not sure about what it does to the impedance/waveform but I thought I would give it a try.

Detector/Instrumentation Amplifier: I chose to use LM358 instead of theLM324, since I needed 6 opamps and the LM324 would have given 4 or 8 and added a wiring complexity that I did not need.

Note: Transformer T1 is ferrite ring 7mm  in diameter and permeability 1000-2000, bifilar – 8 turns

I wrote a  small test program to set the DDS at 14MHz, connected a dummy load and calibrated the analyser by setting the Vin to 1011, V50 to 505, and VL to505. The SWR at this point is 1.0. I then decided to test it further by varying the DDS from 13MHz to 15MHz and displaying the raw values of Vin, V50 and VL on Line 4 of the display and the results on line 1 and 2. You can see the changes in the video.

I’m not sure if the parameters (SWR, R and X of the dummy load should change so widely across the range from 13 – 15 MHz, maybe it does, a resistance test of the dummy load showed it to be 83 ohms.

Check out the video here: HARP

Next steps
It is best to use good quality trimpots to calibrate the meter at the band of interest. Now to make a PCB and test it further.


Antenna Analyser – UT2FW
Analyser-DDS a 500Khz up to 71Mhz antenna-analyser

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SuNDIAL – SigNal DemodulatIon InterfAce (using DigitaL Signal Processing)


DSP Module

Having built simple SDR (Software Defined Radio) front-ends such as the DR-2E (YU1LM) and the Softrock as well as the Ensemble, I had to use a computer running suitable software to demodulate the signals. Several standalone receivers do exist today and so does the technology for building such a standalone module. Scouting around for ideas, turned up this EDEN DSP module (pictured) that will has a 13kHz DSP receive SSB/CW IF system with switched bandwidth filtering, de-noiser and auto-notch.

I sourced the PCB from cumbriadesigns which arrived in the post and set about collecting components and applying for samples from Microchip (DSPIC33FJ64GP306) and the TLV320AIC23BPW (Audio CODEC) from Texas Instruments.Soldering this took about 4hours (SMD soldering is easy if you have right tools), working after-office for an hour each day.

Next steps
I now figure that I require a PICKIT2 programmer running on 3.3v that will allow me to program the DSPIC. I also now have to relearn a bit of ‘C’ to understand the functions and the ready code available on the groups (https://uk.groups.yahoo.com/neo/groups/eden_dsp/info). This will be a step up from the ProtonBasic that I’ve been using so far and I’m looking forward to the challenge.

I am now designing a PICKIT2 board from scratch using an 18F2550 and will have some PCBs made shortly, if all goes well, the PCBs may well be in hand in the next 2 weeks.

Onward ho!!

Disclaimer: I have no association with any of the individuals or organisations listed above.


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D-SPiRiT – Direct digital Synthesis PRojecT

Always wanting an RF Signal Generator that would be able to provide a decent RF Signal, with minimal (zero) drift, the availability of the DDS Module on eBay presented a good opportunity. However, a DDS chip such as the AD9850 would need to be controlled by  a microcontroller (uC). With opportunities come challenges and one of them was the choice of the uC, this was the easy one. Microchip had always been a favourite with my friend Charudatt (VU2UPX) who had been using them successfully for several years.

The next challenge was to learn PIC  programming; which in itself seemed daunting. However, there are several good tutorials, forums and a lot of helpful folk out there on the internet who provided ideas and sample code that became the building blocks of the project. I chose to work with BASIC (Proton IDE) since I knew BASIC and was too lazy to relearn C.


  • – Stable frequency signal: 1Mhz to 55Mhz (approx)
  • – Step Size: 1Hz, 10Hz, 100Hz; 1KHz, 10KHz, 100KHz; 1MHz, 10MHz
  • – User defined memory: 15 Channels (U00 to U14)
  • – WARC Bands: 10 Channels
  • – Configuration: Default Startup Frequency, IF Offset, Clock Calibration

D-SPiRiT_v1.1 (Courtesy – VU2UPX)D_SPiRiT_Locked

The DDS Module
The VFO is based around the inexpensive DDS module available on eBay. There seems to be no problems with the DDS module based on the limited testing that I could undertake.

The Veroboard
I decided to build this on a veroboard and make a prototype before trying it out on a proper PCB. This was made as a set of modules (LCD, Switches, Rotary Encoder, DDS Module. This took several hours of soldering and some quality testing to ensure that there were no solder bridges and wrong connections.


A modular approach

A modular approach

The microcontroller
The PIC16F1847 was suggested by VU2UPX and it is an excellent choice. I was able to cram a lot of features (with code usage about 70% and 21% of variable bytes). I tried a modular approach here too, with some code reuse that I had learnt (Cohesion and Coupling). However, I did not try parameter passing and trying to write a library of common modules and that I think will be my next task for another project. The hex file is available here (D_SPiRiT). Rename the file to .hex

A test of the frequency vs the output signal was carried out at a friend’s QTH (M0GDE) who patiently called out the readings and made notes. We were able to use the Perseus and 60Mhz oscilloscope to provide us the readings.

Points to Note
The DDS module prefers to run on 3v3, and the voltage regulator get quite warm (hot!!)
A finger on the crystal changes the frequency and it does run warm, maybe it’s the voltage


Part 1 – Introduction

Part 2 – Video 2


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