Saturday, January 30, 2021

ADF4351 Signal Generator

 Not much here, just a simple signal generator based on ADF4351 module from "fleebay". PS: there is an improvement over this code at this new post.

 I just needed to generate one single frequency that can go up or down in 100Khz steps via two push buttons. Added an optional LCD to display the main frequency and the third harmonic since I'm using it to verify some equipment on 10Ghz.

Test board:

On the frequency counter:

Schematic based on an Arduino Nano controler:

Spectrum output on lower frequencies (414Mhz) and output level at "0" (add 20db attenuation at the spectrum input):

and the third harmonic:

Power at "3" (second harmonic now visible)

 3rd harmonic as seen on a 10Ghz adapter for a 1.5Ghz spectrum analyzer:
(not calibrated):


 /// code start
   ADF4351 signal generator
   CT2GQV 2020

   Based on code from: ADF4351 example program

   VFO with 100Khz steps starting from a predifined frquency (UL frequencia) using 2 buttons for up and down.
   Display on 16x2 I2C LCD of the frequency set and the third harmonic value
   Also serial output of the main frequency set.

#include <Arduino.h>
#include "adf4351.h"
#include <LiquidCrystal_I2C.h>

#define SWVERSION "1.3"
#define PIN_SS 9  ///< SPI slave select pin, default value
ADF4351  vfo(PIN_SS, SPI_MODE0, 1000000UL , MSBFIRST) ;
unsigned long frequencia = 3333320000UL ; // 3.333.334 (10 Ghz n=3)
// unsigned long frequencia = 2000000000UL ; // 2.000.000 (10 Ghz n=5)
// unsigned long frequencia =    414000000UL ; //    414.000 (10.368 Ghz n=25)
// for 442Mhz use the bellow and comment the above
//   unsigned long frequencia =  442000000UL ; // 442Mhz or 1.326 Ghz , tird harmonic

// I2C LCD virtual pinout
#define I2C_ADDR    0x27  // I2C Address for my LCD, found with I2C scanner
#define BACKLIGHT_PIN     3
#define En_pin  2
#define Rw_pin  1
#define Rs_pin  0
#define D4_pin  4
#define D5_pin  5
#define D6_pin  6
#define D7_pin  7
LiquidCrystal_I2C       lcd(I2C_ADDR, En_pin, Rw_pin, Rs_pin, D4_pin, D5_pin, D6_pin, D7_pin);

// buttons for up/down in frequency, puleed up from 5v with a 10K resistor, analog pin will be short to ground for button press
int button1 = 1;
int button2 = 2;

void setup()
  Serial.begin(9600) ;
  Serial.print("adf4351 VFO CT2GQV "); Serial.println(SWVERSION) ;

  pinMode(button1, INPUT);
  pinMode(button2, INPUT);

  lcd.begin (16, 2, LCD_5x8DOTS); lcd.setBacklightPin(BACKLIGHT_PIN, POSITIVE); lcd.setBacklight(HIGH); // 20x4 lines display LCD
  lcd.setCursor(0, 0);  lcd.print("Signal Generator  ");
  lcd.setCursor(0, 1);  lcd.print("Ver: "); lcd.print(SWVERSION);

  Wire.begin() ;
     setup the chip (for a 10 mhz ref freq)
     most of these are defaults
  vfo.pwrlevel = 3 ; // measured at 3.3Ghz after 1m cable >> "0" = -8 dBm / "1" =  -5.8dbm / "2" = -3.3dbm / "3" = -0.4dbm
  vfo.RD2refdouble = 0 ; ///< ref doubler off
  vfo.RD1Rdiv2 = 0 ;   ///< ref divider off
  vfo.ClkDiv = 150 ;
  vfo.BandSelClock = 80 ;
  vfo.RCounter = 1 ;  ///< R counter to 1 (no division)
  vfo.ChanStep = steps[2] ;  ///< set to 10 kHz steps

     sets the reference frequency to 10 Mhz
  if ( vfo.setrf(10000000UL) ==  0 )
    Serial.println("REF.SET: 10 Mhz") ;
    Serial.println("ERROR: reference freq set error") ;
     initialize the chip
  vfo.init() ;

     enable frequency output
  vfo.enable() ;


  if ( vfo.setf(frequencia) == 0 ) {
    Serial.print("VFO.SET:") ; Serial.println(vfo.cfreq) ;
    lcd.setCursor(0, 0);  lcd.print("F   :"); lcd.print(frequencia/1000);
    lcd.setCursor(0, 1);  lcd.print("F(3):"); lcd.print((frequencia/1000)*3);
  } else {
    Serial.println("ERROR: Set init Frequency") ;

vfo.ChanStep = steps[4] ; ///< change to 100 kHz

void loop()
  int buttonState1 = analogRead(button1);
  int buttonState2 = analogRead(button2);
  // serial debug for the button for +/- frequency
  // Serial.print("B1,B2:"); Serial.print(buttonState1); Serial.print(",");  Serial.println(buttonState2);

// up frequency
  // button pin is puled down to ground...or close to it (100) as long as lower than 2049
  if (buttonState1 <= 100) {
    frequencia += vfo.ChanStep;
    if ( vfo.setf(frequencia) == 0 )
      Serial.print ("VFO.SET: "); Serial.println(vfo.cfreq) ;
      lcd.setCursor(0, 0);  lcd.print("F   :"); lcd.print(frequencia/1000);
      lcd.setCursor(0, 1);  lcd.print("F(3):"); lcd.print((frequencia/1000)*3);
// end up frequency 

// down frequency
  if (buttonState2 <= 100) {
    frequencia -= vfo.ChanStep;
    if ( vfo.setf(frequencia) == 0 )
      Serial.print ("VFO.SET: "); Serial.println(vfo.cfreq) ;
      lcd.setCursor(0, 0);  lcd.print("F   :"); lcd.print(frequencia/1000);
      lcd.setCursor(0, 1);  lcd.print("F(3):"); lcd.print((frequencia/1000)*3);
// end down frequency 

// button software debounce
/// code end

Some other signal generators based on similar modules and also the ADF4355: (for the ADF4355)


Have a nice day!

Wednesday, January 27, 2021

EIP-371 Source Locking Microwave Counter repair

 I've done a previous repair on this device because I got it without being working on the 18Ghz range. I suspect this will not be the last one given it's age.

Anyhow, one of this days I turned it on to check the output frequency of a FVC99 module and it was displaying all entrance selector LED's on (should be one at a time) and no change on the input by pressing the band selector. Also there was no activity on the display for the source locking.

I suspect the usual bad contacts (it's slot based construction) or power supply, more to the power supply side since the equipment hadn't been moved (it's a bit sensitive on moving/vibrations and that had been the cause of the first repair).

 First thing I did was removing and inserting all the boards one by one trying to find the one responsible for the selector LED's, I have the manual but didn't feel like to read it. In the end, had no luck. Then I realized there's another board that does not slide, instead is attached to the side panel. So I moved that one to the side and checked all the connections. 

 Image, now, after connecting back, started working, I can now select the input and have the digits lit:

I can measure again but I'm preparing a home made counter in case this one fails again in the future.

Have a nice day!

Sunday, January 03, 2021

Return loss bridge

 Small project made last year (4 days ago) just for fun and to try out the SWR feature of the spectrum analyzer.

Design is based on this one to the exception of the ferrite material, I used 43 instead of 77.

RF source will be the tracking generator, load will be device under test and detector the spectrum analyzer RF input.

For the 50 Ohm resistors (R1,R2,R3) I used two leaded 100 Ohm in parallel, SMD and shorter leads between components would help more on the high frequency side of the spectrum.


 Some data taken:

With no load connected in one direction and then the opposite one (cable swap), if all is perfectly balanced it should show equal lines, in this case....almost there, in any case the return loss line is all but flat...

Now measuring a 50 Ohm load, ideally should give the lowest possible result and a flat line for all the frequency range:

At 1.6Mhz: 1.22, so not very usable at the low range, probably due to lack of inductance on the core.

At 10.8 Mhz, 1.05, much more inline with and expected result (very low VSWR).

At 152 Mhz looks like it starts to break the measurement again.

And forget it at 433 Mhz since it's too off.

The load used was a Narda 370 BNM, 5W and good to 18Ghz.

Basically it's very usable on the HF range or just as general curve tracer for antenna VSWR at VHF frequency ranges.

You can also take the same info without the SWR measurement option on the Spectrum Analyzer, just use the tracking generator, normalize in the open position (no device under testing connected) and then look for the SWR from the return loss measured, you can use this table or calculate it yourself.


Have a great Year!