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:
- the Divider IC (U2), and
- the Mixer IC (U3)
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..
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.
|Band||Divider Output Freq|
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.
(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)(go directly to build notes)
Divider Bill of Materials
Stage Bill of Materials
|❏||1||2 X #4-40 hdw (nut, bolt, washer, spacer)||HDW|
|❏||3||0.01 uF||(smt)||SMT 1206|
|❏||4||0.1 uF||(smt) black stripe||SMT 1206|
|❏||1||74AC74 Dual D FF||74AC74||SOIC-14|
|❏||1||FST3253 mux/demux switch||FST3253||SOIC-16|
Divider Summary Build Notes
- Install remainder of the SMT Capacitors
- Install U3
- Install U2
- Install Hardware
- Test the Stage
Divider Detailed Build Notes
Bottom of the Board
Install remainder of the SMT Capacitors
We will use this stage to go ahead and install all of the remaining SMT bypass capacitors.
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)
|❏||C14||0.01 uF||(smt)||SMT 1206|
|❏||C21||0.01 uF||(smt)||SMT 1206|
|❏||C15||0.01 uF||(smt)||SMT 1206|
|❏||C16||0.1 uF||(smt) black stripe||SMT 1206|
|❏||C17||0.1 uF||(smt) black stripe||SMT 1206|
|❏||C18||0.1 uF||(smt) black stripe||SMT 1206|
|❏||C19||0.1 uF||(smt) black stripe||SMT 1206|
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.
|❏||U3||FST3253 mux/demux switch||FST3253||SOIC-16|
Take ESD precautions
Install 74AC74 (U2) on the SOIC-14 pads on the bottom side of the board. Take ESD precautionsSee hints on installing SMT ICs. >
|❏||U2||74AC74 Dual D FF||74AC74||SOIC-14|
Take ESD precautions
Top of the Board
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.
|❏||hdw1||2 X #4-40 hdw (nut, bolt, washer, spacer)||HDW|
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)
- 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
|With the 100 ohm current-limiting resistor||mA||< 20||18.0||_______|
|Without current limiting resistor||mA||< 25||18.1||_______|
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.
|Pin 3||Vdc||3.5 - 4.5||4.1||_______|
|Pin 11||Vdc||3.5 - 4.5||4.1||_______|
- 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.