Theory of Operation

The Dividers stage takes in the local oscillator's signal and divides it by 4, producing two output signals. Each output signal is at a frequency that is ¼ the stage's input signal and is a square wave with 50% duty cycle.  The 50% duty cycle is with respect to the4 5V rail.

The signals are "in quadrature", that is, they are 90° out of phase with each other. These are provided to the TX and RX mixer stages as clocking signals. They are called out on testpoints marked S0 and S1.


This is a subset of the overall schematic. Note: red dot indicates resistor testpoints (hairpin, top, or left-hand lead)
04 Dividers

Bill of Materials

C210.01uFSMT 1206

Summary Build Notes

  • Install C21 (bottom)
  • Install SMT U6 (bottom)
  • Install 2 resistors (top)
  • Install 1 ceramic capacitor (top)
  • Test the Stage

Detailed Build Notes

Bottom of the Board

Install U6

U674AC74 SMT SOIC-14

Install C21 SNT Cap

C210.01uFSMT 1206

Top of the Board

Install Resistors


Install Ceramic Capacitor


Completed Stage


Completed topside


Completed bottomside


Current Draw(DMM)

  • Current numbers here are for the CMOS version of the Si570.  You will need to adjust these up by about 14 mA for the LVDS version.
  • Power the board up
  • Measure the current draw and 5 V rail voltage with a 1K Ω limiting resistor
  • Measure the current draw without the limiting resistor.
TestpointNominal ValueAuthor'sYours
Current Limited mA6-10 mA7.5 mA______
Current limited 5V rail1-2 Vdc975 mV______
Non limited draw mA80-90 mA85.7 mA______

Voltage Tests (DMM)

If the output of the dividers are not as expected, check the voltages at the pins of U6. Unexpected values here usually point to problems with soldering U5 and/or the voltage dividing resistors R9 and R10. Using a DMM:

  • Measure the output of the voltage divider with respect to ground. Measure at the top lead of R10 (or the left-hand lead of R9).  This should yield approximately ½ the 5 volt rail voltage.
  • Measure the voltages (with respect to ground) on the pins of U6.  It is best to test for these voltages at the actual pins (not the pads), thereby ensuring correct soldering of the pins to the pads.

TestpointNominal ValueAuthor'sYours
Topside, R10's top lead2.5 Vdc2.50 Vdc______
U6, Pins 1, 4, 10, 13, 145 Vdc4.96 Vdc______
U6, pins 2, 3, 5, 6, 8, 9, 11, 122.5 Vdc2.48-3.50 Vdc______
U6, pin 70 Vdc0 Vdc______

Test Center Frequency Output

  • Connect a short piece of wire as an "antenna" for your HF RX and lay it over the board
  • No need to use the USB control in this test
  • Apply power to the board
  • Tune your radio to find the signal at 14.084 MHz (¼ the Si570 default frequency of 56.336 MHz
  • If you can detect the signal and have passed the voltage tests above, your divider stage is pretty well assured to be working correctly.

U5 Output (Optional Test)

In the event that you have or have access to a dual channel oscilloscope, you can test the divider outputs here. 

Do not attempt this measurement unless you have a calibrated scope of very good quality and correctly compensated probes.

Testpoint for Dividers Stage

U5 sends I and Q signals to the mixer's S0 and S1 inputs. 

  • Use a dual channel oscilloscope, triggering on Channel 1
  • Power up the board and plug in the USB cable
  • Run Rocky and set the center frequency to 7.046 MHz
  • measure the S0 and S1 outputs at the corresponding testpoints on the top side of the board, as indicated above.
  • They should both be the same frequency (¼ of the LO Output - assuming you use the settings from the LO test, that would be 7.046 mHz) and should be in quadrature (90° out of phase with each other).  The image below shows approximations of p-p voltages and frequencies of the 2 quadrature signals. 
  • They should be approximately 5 volt p-p square waves. The square waves may have a fair amount of ringing on them depending a bit on your scope quality and connection to the circuit board (see Waveforms below).

Divider Output Waveforms (Quadrature, 7.046 MHz)

Divider Output Waveforms
Power Supply Mixer Stage Local Oscillator STage