Dividers Introduction

Theory of Operation

This stage divides the output of the local oscillator by 4 (or, in the case of the 80 and 160m kits, by 8, based on the JP1 setting) and produces the clocking outputs for the Mixer stage.

The output is two signals, in quadrature (i.e., 90 degrees apart), at the desired center frequency, except for the 20m and 15m kits, where the output is one-third of the center frequency. In those kits, the desired center frequency is actually the third harmonic of the divider output frequency.

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Dividers Schematic

(Resistor testpoints (hairpin, top, or left-hand lead), as physically installed on the board, are marked in the schematic with red dots)

(Click for Full Schematic)
Dividersschematic

(go directly to build notes)

Dividers Bill of Materials

Stage Bill of Materials

(resistor images and color codes courtesy of WIlfried, DL5SWB's R-Color Code program)

CheckDesignationComponentMarkingCategoryOrientationNotesCircuit
❏U374HC74 Dual-D FF74HC74 74HC74SOIC-14Dividers
❏U274HC74 Dual-D FF74HC74 74HC74SOIC-14Dividers

Dividers Summary Build Notes

Dividers Detailed Build Notes

Bottom of the Board

Dividers Bottom View

Install U3

Install 74HC74 (U3) on the SOIC-14 pads at the bottom of the board. Take ESD precautions

CheckDesignationComponentMarkingCategoryOrientationNotes
❏U374HC74 Dual-D FF74HC74 74HC74SOIC-14
Take ESD precautions

Top of the Board

Dividers Top View

Install U2

Install 74HC74 (U2) on the SOIC-14 pads at the top of the board. Take ESD precautions

CheckDesignationComponentMarkingCategoryOrientationNotes
❏U274HC74 Dual-D FF74HC74 74HC74SOIC-14
Take ESD precautions

Dividers Completed Stage

Top of the Board

View of Completed Top

Bottom of the Board

View of Completed Bottom

Dividers Testing

Warning

Test Setup

Take appropriate ESD precautions in these tests, since you will be working around the divider IC

Visual Inspection

Test Setup

Using very good lighting and magnification, carefully inspect the solder joints to identify bridges, cold joints, or poor contacts.

Pay especial attention to the joints on the divider IC pins. If necessary, touch up the joints with your iron and/or some flux. Wick up any excess.

Current Draw

Test Setup

  • connect a 1k ohm resistor in series with the positive power lead
  • apply 9 Vdc and measure the current draw with the limiting resistor in place
  • remove the current limiting resistor
  • apply 9 Vdc and measure the current draw without the limiting resistor

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
Current draw WITH 1k ohm current limiting resistormA< 96.1_______
Current draw without the limiting resistormA20-3024.4_______

U2 Pin Voltages

Test Setup

Measure the voltages with respect to ground for each of the pins of U2. Tage care to measure at the actual IC pin rather than the pad, so as to ensure you are measuring the PIN voltage

expected voltages are indicated in the table below:

  • 5 V (range of 4.5 - 5.4)
  • 2.5 V (approx 50% of the 5B rail value)
U2 Pin Voltages

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
Pin 1Vdc54.92_______
Pin2Vdc2.52.47_______
Pin3Vdc2.9 - 3.53.21_______
Pin4Vdc54.92_______
Pin5Vdc2.52.44_______
Pin6Vdc2.52.47_______
Pin7Vdc00_______
Pin8Vdc2.52.47_______
Pin9Vdc2.52.43_______
Pin10Vdc54.92_______
Pin 13Vdc54.92_______
Pin 14Vdc54.92_______

U3 Pin Voltages

Test Setup

Same instructions apply as for U2

U3 Pin Voltages

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
Pin 1Vdc54.92_______
pin 2Vdc2.52.47_______
pin 3Vdc2.52.44_______
pin 4Vdc54.92_______
pin 5Vdc2.52.45_______
pin 6Vdc2.52.47_______
pin 7Vdc00_______
pin 8Vdc2.52.47_______
pin 9Vdc2.52.44_______
pin 10Vdc54.92_______
pin 11Vdc2.52.47_______
pin 12Vdc2.52.44_______
pin 13Vdc54.92_______
pin 14Vdc54.92_______

Divider Output

Test Setup

  • The divider divides the LO freuqncy by 2, twice. First in U2 and then in U3.
  • The first division produces two signals that are at &frac2; the LO freqiency and 180 degrees out of phase with each other
  • The second produces 2 frequencies that are at &frac4; of the LO frequency and are 90 degrees out of phase with each other.
  • Using a ham receiver, dial up 28.224 MHz and couple a wire from its antenna to point A and then point B on the graphic below. You should hear the signal in the receiver.
  • Dial up 7.056 MHz and similarly couple the wire to point C and then point D, below. You should hear the signal.
Divider Output

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
Point A (see above graphic)MHzreceive at 14.112received_______
Point B (see above graphic)MHzreceive at 14.112received_______
Point C (see above graphic)MHzreceive at 7.056received_______
Point D (see above graphic)MHzreceive at 7.056received_______

Divider WaveForms - First Division

Test Setup

This test can only be done if the scope used is a good quality, calibrated scope with correctly compensated probes (unlike the author's cheapo scope which encounters excessive overshoot at higher frequencies)

  • Set the scope up for dual trace measurement, triggering on Channel 1 (so as to get the phase relationships)
  • Poweer up the board
  • Place one probe on testpoint A and the other on testpoint B
  • use a 10X probe and set the scope magnification to 10x)
  • Set the horizontal division to 40 ns and the vertical to 1V p-p per division
  • Measure the results
  • Should see something similar to the graphic below (14.114 MHz at around 5 Vp-p)
Divider WaveForms - First Division

Divider Waveforms - Second Division

Test Setup

  • Set the scope up for dual trace measurement, triggering on Channel 1 (so as to get the phase relationships)
  • Power up the board
  • Place one probe on testpoint C and the other on testpoint D
  • Set the horizontal division to 40 ns and the vertical to 5V p-p per division
  • use a 10X probe and set the scope magnification to 10x)
  • Measure the results
  • Should see something similar to the graphic below (7.056 MHz at around 5 V pk-pk)
Divider Waveforms - Second Division