Thursday, 21 March 2019


Google cuts off blogs

Google has just removed the API that allows the blog editor I use "Mars Edit" from uploading images to their Picassa image storage. This means that I cannot any longer write articles with pictures or presentation slides.

This is a disaster.

So I will for now stop this blog. Information about my own and club projects, and Arduino sketches for radio applications, can be found at FTP download web site.

Please have a look there for project information. It is organised like this

ALL ARDUINO SKETCHES - for every project Sketches can be found here. Download and copy/paste into a new Arduino sketch, and save locally

CLUB PROJECTS - the projects I have run at our local radio club

MY PROJECTS - personal develpoments which may be of interest

TECH INFO - a random collection of techncial information which may be helpful

73 to all

Antony M0IFA

Friday, 15 March 2019

Thursday, 14 March 2019

SSB Exciter Hardware

This is the hardware design, so far, for the minimal SSB exciter. It has been made as simple as possible, and does not give a super performance. It was developed to illustrate the principle of SSB generation.

SSB Exciter 001 SSB Exciter 002 SSB Exciter 003 SSB Exciter 004 SSB Exciter 005 SSB Exciter 006 SSB Exciter 007 SSB Exciter 008 SSB Exciter 009 SSB Exciter 010

Sunday, 3 March 2019

The FT8 world's gone mad

It's Sunday, the day when all radio amateurs find the chance to get in their shacks. And wow are they hitting the airwaves today, with FT8's 3kHz bandwidth around 7074kHz jam packed full. Look:

Screenshot 2019 03 03 at 16 56 07

This is the signals from my tiny loop antenna fed directly to my Elektor Arduino/SDR.

If you're a MacOS man...

Windows is not the dominant OS these days, many are using Linux and many more MacOS on Apple computers. But the world of Amateur radio is poorly served by manufacturers, especially SDR transceiver people, for the Mac. So here's what I have found so far

I am using the windows emulator Crossover (basically a graphic front end to the open source "Wine" system.

MACOS native apps

1. MultiMode Cocoa - just about every digital mode supported, PSK31, SSTV etc

2. cocoaModem - another app supporting digital modes, including here Hellscriber

3. MultiScan - for SSTV

4. fldigi - well known digi-mode app

5. SDR Radio - a rather poor SDR program, great, simple interface but poor config and audio management

6. gqrx - works well for rTL sticks

7. cubicSDR - the out and out winner SDR program. But a bit "industrial", not a friendly interface

8. WSJT-X - the must have FT8 app

9. GridTracker - nice visual of stations on a map, has useless features

10. JT-BRIDGE - pretty, display of stations, country, distance away, etc, but for what?

11. JSCAll - the new "FT8-like" full message app. Does not fully work as a Mac app, and the interface is poor

WINDOWS - if you must

I just moved from using Crossover (a kinda Wine GUI) to running Parallels and installing Windows 10. This all works smoothly but gobbles up RAM. Better to have 32GB if you can, just about works on my MacBook with 8GB. USB and Audio interfaces are problematic, but with enough digging into the terrible old fashioned Windows control panels they can be got to work, I think - it's early days. Anyway I have HDSDR running at 96kHz input (+/-48kHz displayed). I am checking to make sure ELADs FDM-SW2 will run OK under Windows, as I am thinking of buying an FDM-DUO SDR transceiver. A very modern SDR design.

Thursday, 28 February 2019

JS8 Call

Largely based on the well known WSTJ-X, FT8 software, there is a new one called JS8CALL. FT8 sends brief 13 character messages in 15 second slots. JS8 extends this to send longer messages in one or more slots. Thus allowing a two way open chat. FT8 for 40m is based at 7074kHz USB, JS8 is higher at 7078kHz USB. This is so far what I have received:

Screenshot 2019 02 28 at 17 08 59

Showing the FT8 mass of signals at 7074kHZ and a single solitary JS8 signal just above 7078kH - as received on the Hack Green web SDR. And this is a decode of signals received on my Elektor SDR receiver:

Screenshot 2019 02 28 at 16 26 22

Thursday, 21 February 2019

SSB Exciter project - Arduino sketch

Of course the other challenge of the SSB Exciter project is writing the Arduino sketch to control the three outputs of the Si5351 synthesiser. The sketch will run on an Arduino Nano with limited program memory, so can't be too fanciful and must be optimised throughout.

It needs to generate three outputs. CLK0 will be a 7.0-7.2MHz frequency for the VFO of the DCRX Direct Conversion Receiver. CLK1 will be the 11MHz input to the first SSB mixer (11054.8kHz for USB generation. CLK2 must be the mixing frequency to get the USB & LSB 11MHz signals to a final 7.0-7.2MHz for the 40m band. This is done by outputting SSB - freq for USB and a SSB + freq for LSB.

The code runs on the SIGGEN hardware designed during the BARSicle project (see many previous postings), an Arduino Nano drives an OLED display and a three output Si5351 synthesiser module, controlled by a rotary encoder with push switch.

The rotary encoder will tune in 10kHz to 10Hz steps, chosen by a short push on the encoder switch. A long 'hold' on the switch will change from USB to LSB and back. The OLED display will be simple, showing the tuned frequency (in kHz 7000.00 to 7200.00)), the sideband (USB or LSB) and the tuning step (10H to 10kHz). The previously written "Oled.h" header file using the u8g2 library will format these displays.

Here's the initial code, not yet available for download but can be cut and pasted from here, The libraries are part of previous downloads available (look below)

// CLK0 = RX, CLK1 = SSB (11MHz), CLK2 = VFO (4 | 18MHz)

#include "Oled.h"                                         // include header
#include "si5351.h"                                       // include library
#include "Rotary.h"                                       // include library

#define CLK 3                                             // encoder connnections
#define DT 2                                              // reverse 2&3 if wrong direction
#define SW 4
#define HOLD 500                                          // held button time > 0.5sec

#define CALIBRATION -150000                               // frequency CALIBRATION

#define SSB 1105480000                                    // SSB USB freq

Si5351 dds;                                               // create dds object
Rotary enc = Rotary(CLK, DT);                             // create enc object

uint64_t freq = 700000000;                                // first init freq (cHz), 7MHz
uint64_t freqStep = 100000;                               // init step (cHz), 1kHz

bool sideband = true;                                     // start on USB

void setup() {
  pinMode(CLK, INPUT_PULLUP);                             // encoder inputs, with pull-ups
  pinMode(DT, INPUT_PULLUP);
  pinMode(SW, INPUT_PULLUP);

  oled.begin();                                           // begin OLED

  dds.init(SI5351_CRYSTAL_LOAD_8PF, 0, CALIBRATION);      // set xtal capacitance, 25MHz, & CALIBRATION

  dds.drive_strength(SI5351_CLK0, SI5351_DRIVE_8MA);      // output drive (~+10dBm)
  dds.drive_strength(SI5351_CLK1, SI5351_DRIVE_8MA);      // output drive (~+10dBm)
  dds.drive_strength(SI5351_CLK2, SI5351_DRIVE_8MA);      // output drive (~+10dBm)

  dds.output_enable(SI5351_CLK0, 1);                      // enable
  dds.output_enable(SI5351_CLK1, 1);                      // enable
  dds.output_enable(SI5351_CLK2, 1);                      // enable

  freqOut(freq);                                          // output initial frequencies

  dispUpdate();                                           // display

void loop() {
  long hold;                                              // button hold time
  unsigned char result;                                   // encoder result

  if (digitalRead(SW) == LOW) {                           // enc button push
    hold = millis();                                      // start hold count
    while (!digitalRead(SW));                             // wait release
    if (millis() - hold > HOLD) {                         // button hold > HOLD time, change sideband
      sideband = !sideband;
      freqOut(freq);                                      // update frequencies
    else if (freqStep == 1000) freqStep = 1000000;        // update step if 10Hz -> 10kHz
    else freqStep = freqStep / 10;                        // step down
    dispUpdate();                                         // display

  result = enc.process();                                 // read encoder
  if (result == DIR_CW) {                                 // freq up
    freq += freqStep;
  if (result == DIR_CCW) {                                // freq down
    freq -= freqStep;

// CLK0 = RX, CLK1 = SSB (11MHz), CLK2 = VFO (4 | 18MHz)
void freqOut(uint64_t freq) {
  dds.set_freq(freq, SI5351_CLK0);                         // RX freq 7MHz
  dds.set_freq(SSB, SI5351_CLK1);                          // SSB freq 

  if (sideband) {
    dds.set_freq(SSB - freq, SI5351_CLK2);                 // VFO USB freq
  else {

    dds.set_freq(SSB + freq, SI5351_CLK2);                 // VFO LSB freq

void dispUpdate() {                                        // picture loop
  do {
    dispMsg(35, 0, "SSB TCVR");                                 // display title
    dispFreq(15, 20, freq / 100, 0, 2);                    // display frequency, in kHz
    if (sideband)
      dispMsg(10, 50, "USB");
      dispMsg(10, 50, "LSB");
    dispStep(80, 50, freqStep / 100);                      // display step freq
  } while ( oled.nextPage() );

Monday, 18 February 2019

SSB Exciter project - XTAL FILTER

So the next step is to try out a Xtal filter. I have four 11059.2kHz xtals and have wired them up like this

IMG 0082

I tried them out on the breadboard, which is not the best place to build a xtal filter! I connected the input directly to the Si5351 SIGGEN output and measured the response using my RF Meter. The breadboard now looks like this

IMG 0970

This is what I got

Screenshot 2019 02 18 at 16 15 28

The filter is 2.9kHz wide. And to generate USB the carrier should be at 11056.2kHz, and for LSB 11059.1kHz. All is looking good. The circuit now needs an output buffer. When I have built this I will have basically the first half of my exciter done.

SSB exciter project - 1st MIXER

One of the projects I want to get "under my belt" is an SSB exciter. It has always seemed to me to be a black art or magic to generate SSB signals. I mean I know on paper how its done, but to build a system...? That's another matter. Anyway I have started, this is the plan

Screenshot 2019 02 18 at 13 18 05

The first mixer will generate DSB signals at 11MHz, this will be sent to a xtal filter with a bandwidth of 2.5-3kHz, this sill then go to a 2nd mixer with inputs at 4 or 18MHz to be mixed down to 7MHz LSB or USB, finally there will an output amp to give at least +10dBm output.

The mixers will be the commercial SBL-1 double balanced mixers which have an excellent performance.


Here's my schematic for the 1st mixer

1st MIXER sch

The RF input is at a relatively high level to switch the internal mixer diodes, it comes straight from the "0" output of a Si5351 frequency synthesiser. The audio input is via a 51R "load" resistor, it currently comes from my Audio Synthesiser (see previous posting) which has an LM386 output amplifier. The level is 200-300mVrms. The RF output is across the 20uH choke (10t/FT37-43) loaded by a 150R resistor - which will be the input impedance for the xtal filter.

Here's the breadboard

1st MIXER bb


These are two shots of the output. I used a simple Elektor SDR receiver, via a 40dB attenuator and into my MacBook running the Cubic SDR program.

Screenshot 2019 02 18 at 13 44 40

Screenshot 2019 02 18 at 13 44 25

I am running it at 11MHz. As you can see the output is the two sidebands 1kHz away from the centre frequency.

Monday, 11 February 2019

Finished Audio SIGGEN

I have boxed up the Audio SIGGEN. This provides an output of up to +10dBV, 3.2V rms and can drive a low impedance load. The frequency range is from 10Hz up to 100kHz in steps of 10, 100, 1KHz and 10kHz. It operates from a 12V supply.

Inside the box are an Arduino UNO, an AD9833 digital frequency synthesiser with analog output (scanned ROM) and an LM386 audio amplifier.

IMG 0885

Operating with my home built 12V power linear supply

IMG 0884

Thursday, 31 January 2019

Update on Digital Audio Siggen

I have made what I hope will be the last update to the Digital Audio Siggen. This is to use an LM386 as the output amplifier. I bought an amazing kit for £1.56 on eBay, a complete amplifier with gain control!!! So the schematic is now this:

ASG sch

If other decide to build this, I will do a PCB. This is the hard wired prototype.

IMG 0883

The output is up to a little above 10dBV up to 100kHz - pretty good for the LM386!

Code update here

Sunday, 6 January 2019

Sythesised Audio Oscillator

While many struggle to build audio signal generators using phase shift networks, voltage and gain stabilisers and bunches of op-amps, there is another solution. Digital synthesis.


The AD9833 is an IC designed for generating Sine, Triangle or Square waves from 0Hz up to +10MHz. It is simple to use with an Arduino to build a variable frequency sine wave generator. Combined with a Rotary Encoder and an OLED display an accurate audio generator can be made for about 20€!

Here's the circuit.

IMG 0835
And here's the mockup

IMG 0834

Code here.