Divider Introduction


This stage will actually involve installing the remainder of the bottom-side SMT capacitors. In addition to the remaining SMT capacitors, you will also install two of the three bottom-side ICs:

Normally, the Mixer chip (U3) would be addressed in a separate "Mixer" Stage. However, due to the close proximity of the pads for the two Ics, U2 and U3, you will install it in this "Dividers" Stage.

The tests for U3 will be postponed until the "Mixer" Stage.


Theory of Operation

The dividers accept as input the output of the local oscillator and divide that down to two signals that are ¼ the input frequency and in quadrature (90 ° out of phase with each other).

U2 is wired as a divide-by-4 synchroneous divider, clocked by the output from the Local Oscillator. Synchroneous clocking means that all stages switch at the same time, potentially offering a reduction of noise generated during switching.

The divider provides two LO outputs which clock Mixer, U3. Proper Operation of the Dividers may be monitored on a CW or SSB receiver tuned to Divider Output Frequency listed in the table below.

BandDivider Output Freq
160m1.843 MHz
80m3.522 MHz
40m7.056 MHz
30m3.375 MHz
20m4.6825 MHz
15m7.015 MHz

Note 1: A beat note should be heard when the antenna lead connected to a CW or SSB Receiver - tuned to Divider Output Frequency, is held near U2 on the SR Lite II PCB.

Note 2: All frequencies may be slightly below those stated in the table because of the loading capacitance is a little higher than specified for the nominal frequency of the Crystals supplied.

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Divider 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)

(above schematic has clickable areas that can be used for navigation)

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Divider Bill of Materials

Stage Bill of Materials

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

12 X #4-40 hdw (nut, bolt, washer, spacer) HDW
30.01 uF(smt) (smt)SMT 1206
40.1 uF(smt) black stripe (smt) black stripeSMT 1206
174AC74 Dual D FF74AC74 74AC74SOIC-14
1FST3253 mux/demux switchFST3253 FST3253SOIC-16

Divider Summary Build Notes

Divider Detailed Build Notes

Bottom of the Board

Divider Bottom View

Install remainder of the SMT Capacitors

We will use this stage to go ahead and install all of the remaining SMT bypass capacitors.

See hints on installing SMT Caps.

The pads for the 0.1 uF capacitors are highlighted in white on the board shown above. These capacitors are in carrier strips marked with a black stripe.

The yellow markings pertain to the 0.01 uF capacitors.

Be very careful when soldering the SMT capacitors, so as to avoid solder "splashover" that could clog the thru-holes for components installed later on in the project. The holes that are "at risk" are marked with a red dot on the above graphic. You might want to plug them up temporarily with a fine-pointed toothpick when soldering in their vicinity. The at-risk holes are associated with the following capacitors:

  • C14 (the T1 secondary hole to the right of the cap)
  • C18 (R9's barrel hole at the bottom right of the cap)
  • C19 (R10's barrel hole at the bottom right of the cap)
  • C21 (R11's hairpin hole above the cap)

C140.01 uF(smt) (smt)SMT 1206 
C210.01 uF(smt) (smt)SMT 1206 
C150.01 uF(smt) (smt)SMT 1206 
C160.1 uF(smt) black stripe (smt) black stripeSMT 1206 
C170.1 uF(smt) black stripe (smt) black stripeSMT 1206 
C180.1 uF(smt) black stripe (smt) black stripeSMT 1206 
C190.1 uF(smt) black stripe (smt) black stripeSMT 1206 

Install U3

You should install the 16 pin Mixer chip (U3) BEFORE installing the 14 pin divider chip (U2), due to layout considerations which could complicate the soldering of the Ics. The mixer will be tested in a later stage.

See hints on installing SMT ICs.

Install U3 photo
U3FST3253 mux/demux switchFST3253 FST3253SOIC-16 

Install U2

Install 74AC74 (U2) on the SOIC-14 pads on the bottom side of the board. Take ESD precautions

See hints on installing SMT ICs.

Install U2 photo
U274AC74 Dual D FF74AC74 74AC74SOIC-14 

Top of the Board

Divider Top View

Install Hardware

At this point you may install the two mounting screws and their associated hardware.

Install them with the screw head on the topside, then the board, then the spacer, then the washer, and finally the nut.

hdw12 X #4-40 hdw (nut, bolt, washer, spacer) HDW 

Divider Testing

Visual Check

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.

(measurements courtesy of Leonard KC0WOX)

Current Draw

Test Setup

  • connect a 100 ohm resistor in series with the positive power lead
    • apply 12 Vdc and measure the current draw with the limiting resistor in place
    • remove the current limiting resistor
    • apply 12 Vdc and measure the current draw without the limiting resistor

    Test Measurements

    TestpointUnitsNominal ValueAuthor'sYours
    With the 100 ohm current-limiting resistormA< 2018.0_______
    Without current limiting resistormA< 2518.1_______

Voltage Tests

Test Setup

Measure the voltages with respect to ground for each of the pins of U2. Take 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 5V rail value)

Note: the voltages at pins 3 and 11 will vary significantly, depending upon the quality of your meter. There is a significant AC component to these voltages that can affect the DC measurement. Generally speaking, anything at or over about 2.5 Vdc is probably OK. My measurements weere with a cheapo DMM bought from a place whose name rhymes with Barber Grate.

Voltage Tests

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
Pin 1Vdc54.9_______
Pin 2Vdc2.52.48_______
Pin 3Vdc3.5 - 4.54.1_______
Pin 4Vdc54.9_______
Pin 6Vdc2.52.47_______
Pin 7Vdc00_______
Pin 8Vdc2.52.48_______
Pin 9Vdc2.52.48_______
Pin 10Vdc54.9_______
Pin 11Vdc3.5 - 4.54.1_______
Pin 12Vdc2.52.47_______
Pin 13Vdc54.9_______
Pin 14Vdc54.9_______

Divider Output

Test Setup

  • The divider provides the QSD clocking signals for the mixer stage, with the frequency determined by the band for your kit. The bands and their QSD clocking frequencies are:
    • 160m: 1.8432 MHz
    • 80m: 3.522 MHz
    • 40m: 7.056 MHz
    • 30m: 3.375 MHz (the mixer will actually use the 3rd harmonic, 10.125 MHz)
    • 20m: 4.6825 MHz (the mixer will actually use the 3rd harmonic, 14.0475 MHz)
    • 15m: 7.015 MHz (the mixer will actually use the 3rd harmonic, 21.045 MHz)
    • The divider divides the LO frequency by 4, producing 2 frequencies that are at ¼ of the LO frequency and are 90° out of phase with each other.
    • Using a ham receiver, dial up the QSD clocking frequency for the band in question and couple a wire from its antenna to point "QSD Clk 0" and then point "QSD Clk1" on the graphic below. You should hear the signal in the receiver.
    <a name=Divider Output"

Mixer Test

Test Setup

The Mixer installation will be tested in a later stage. In the meantime, just carefully examine the soldering and placement of the IC using good magnification and light.
Go to Power Supply Stage Go to Local Oscillator Stage Go to Mixer Stage