ECEN 2420, Electronics for Wireless, Spring 2016
Prof. Zoya Popovic
IN-LAB HOMEWORK 12 – ASSEMBLING THE RADIO
Assigned: April 18th, Turn in: Monday, April 25th in last Homework Session 6:30pm-9:30pm
This is the last homework for the semester. You will be doing it in teams of odd and even groups
since we need to go through the entire radio.
1. Gather all the boards (1-9).
a. Identify the function of each board in the overall block diagram below.
b. Identify the boards, as well as their inputs (Ij, j=1-9) and outputs (Oj, j=1-9) in the
circuit diagrams below (circle and label them).
2. Identify all the connections between the boards and draw them in color, e.g. Cij would be
the connection between boards i and j (if there is such a connection).
3. Get a TA to sign when you are done.
TA signature: ___________________________________________
We will now follow the signal in the receiver and transmitter and make sure all the boards are
working.
Q1: In the receiver switch, what are the settings of all inputs to the board when the switch is
OFF: _____________________________________________________________________
ON: ______________________________________________________________________
Q2: What is the function of C1?
__________________________________________________________________________
Q3: What is the output frequency from the receive mixer? __________________________
Q4: What is the most important property of the IF filter circuit that you need to pay attention to?
____________________________________________________________________________
Q5: What is the function of C17?
______________________________________________________________________
Q6: When you test the output of the product detector, what frequencies do you expect to see, and
why do you need a 10-nF capacitor across pins 4 and 5?
_______________________________________________________________________
_______________________________________________________________________
Q7: What is the function of the AGC part of the circuit?
_______________________________________________________________________
Q8: Identify all the DC inputs in the receiver (pins and voltages). Identify all the grounds. Mark
them with red and green.
Q9: What are the settings of the transmitter switch when it is
ON: _____________________________________________________________
OFF: _____________________________________________________________
Q10: What voltage gain do you expect from the amplifier chain?
Buffer: __________________
Driver:________________ PA:______________
Total: ____________________
Q11: If you achieve a peak voltage of ~7V at the output, what is the power across a 50-ohm
filter-antenna load?
________________________________________________________________________
Q12: What is the function of C34?
______________________________________________________________
Q13: What is the function of C39?
______________________________________________________________
Q14: What is the function of D12?
_______________________________________________________________
Q15: What elements adjust the frequency of the VFO?
_______________________________________________________________
Q16: If your VFO frequency does not go below 2.2MHz for the extreme setting of the control
element (we need 2.1), what are some things you could do to bring it down?
________________________________________________________________
Radio assembly (on Monday, 25th):
Initial Settings
1. Familiarize yourself with the location of the jacks (J1, J2, J3, & J4), the switches (S1 &
S2), the trimpots (R6, R8, & R13), the trimmer capacitors (C1, C2, C17, C34, C39, &
C50), and the potentiometers (R2, R16, R17). Accidentally adjusting a previously
adjusted component may force you to start the entire procedure over!
2. Connect the knobs to potentiometers R2, R16, and R17 with R2 and R16 having the
small knobs and R17 having the large knob. Make sure that when the screws are tight the
knobs are positioned as shown below when looking at the knob from the front of the
radio.
Minimum
0%
Halfway
50%
Maximum
100%
3. Make a DC power cable with ~24” of wire to connect to J2 (DC power). Note the
connector is a 2.1mm x 5.5mm barrel connector with the center pin being the positive
voltage and the shell being negative. Diode D7 protects the Norcal 40A if the polarity
of the DC voltage is reversed.
4. Do NOT plug anything into J3 (key jack).
5. Plug a bare 3.5mm stereo jack into J4 (audio jack).
6. Do NOT follow the assembly manual for pre-setting the trimmer capacitors as the
capacitors provided in our kits are different than the ones in the official Norcal 40A kits.
Look at the top of the trimmer capacitors and you will see a half moon shape soldered to
the small adjusting screw. This half moon shape should be positioned so that the ends of
it are symmetrical to both pins of the trimmer (50% capacitance) WITHOUT regard to
the angular position of the adjusting screw slot.
7. Set the trim-pots. as follows:
a. R6 (AGC) fully clockwise (100%) = AGC disabled
b. R8 (Audio) fully clockwise (100%) = maximum audio volume
c. R13 (Drive) fully counter-clockwise (0%) = minimum transmitter drive
8. Set the potentiometers. with knobs as follows: (see step #2 above for knob position)
a. R2 (RF gain) fully clockwise (100%)= maximum RF gain
b. R16 (RIT) at 50%
c. R17 (Frequency tune) at 50%
9. Set C50 (air variable) at 50% (plates meshed halfway)
10. Set C1, C2, C17, C34, and C39 to 50% as shown below
Flat
Side
Max. "C"
50% "C"
Min. "C"
11. Set S1 (Power) lever down = power off
12. Set S2 (RIT enable) lever down = RIT disabled
13. Do not connect anything to J1 (antenna jack) yet
TA signature: _______________________________________
Checkout
All steps must be completed successfully before proceeding to the next step!
1. Set the DC power supply to 12.0V and the current limit to 100mA.
2. Connect the power cable to the Norcal 40A and turn on S1. The DC current draw should
be~15-18mA.
a. Measured DC current draw = __________
3. Plug a 3.5mm stereo plug into J3 (key jack) and short tip to sleeve on the plug or plug in
the “Key” and press down. The DC current draw should be ~25-55mA. Radio is now in
the transmit mode at minimum power.
a. Measured DC current draw = __________
4. Remove the plug from J3 returning the radio to receive mode.
Calibration
The radio will be calibrated at 7.040MHz which will be the center of the VFO range. Again all
steps must be completed successfully before proceeding to the next step!
1. Preliminary setup:
a. Set the signal generator for 4mVpp into 50 ohms at 7.040MHz and turn on the
generator output.
b. Connect a coax cable from the signal generator to the 40dB attenuator and another
coax cable from the 40dB attenuator to the Norcal 40A.
c. Set the oscilloscope amplitude to 200mV per division and the time base to 200nS
per division. Set the channel for a X10 probe and AC coupling. Have the scope
measure frequency and Vpp. The next step requires a X10 scope probe (borrow
one for this step). Connect the scope probe to the test point wire near S2 and the
scope ground to the ground loop near J1.
2. Turn on the Norcal 40A (Switch S1= up) and adjust C50 with a plastic tool until the VFO
frequency is correct.
a. With a 10:1 probe the signal is ~600-800mVpp.
b. Adjust C50 (with R17 at 50%) until the VFO frequency is 2.125MHz.
c. Measured frequency (to +/-100Hz) with R17 fully counterclockwise =
____________
d. Measured frequency (to within +/-100Hz) with R17 fully clockwise =
____________
e. Return R17 until frequency = 2.125MHz exactly.
f. What freq. range would you expect the radio to tune? ______________________
3. From now on either a X1 or X10 scope probe may be used but make sure to set the scope
accordingly for the probe used.
4. Receiver alignment
a. Set the scope amplitude for 200mV per division (should already be there) and the
time base to 2ms per division. Connect the scope to tip and sleeve (ground on
sleeve) on the plug connected to J4 (audio)
b. Alternately adjust C1 and C2 for maximum amplitude making sure you have 2
peaks for a 360 degree revolution. Readjust RF signal generator frequency very
slightly looking for the center of the passband. This means that each step in
frequency either side of center of the RF generator reduces the audio amplitude by
the same amount. The generator should already be very close to the correct
frequency (~7.040MHz.) if R17 has not been bumped.
c. Adjust C17 for an audio frequency of 575 +/- 10Hz.
d. What is the measured audio voltage? _____________ (should be >1 Vpp)
e. Adjust the RF signal generator frequency up and down looking for a 6dB change
in amplitude (amplitude is 0.5 times the maximum @ -6dB).
f. Measure the audio frequency at both 6dB points.
g. What is the measured 6dB bandwidth of the crystal filter? _______________
h. Adjust the RF signal generator frequency until the audio frequency is back to
~575Hz.
i. Turn on the Receiver Incremental Tuning (RIT) by turning switch S2 = up and
turn potentiometer R16 throughout its range. The audio frequency should vary
several hundred Hz and you should see the amplitude change as the receiver’s
passband is tuned above and below the frequency of the signal generator.
j. Turn off the RIT (switch S2 = down) which will return the audio frequency to
~575Hz.
k. Adjust R6 (AGC) until the voltage at the scope drops by about 30%. Pot should
be at ~60% of clockwise rotation.
l. Disconnect the RF generator from the 40dB pad while leaving the pad connected
to J1.
5. Transmitter alignment
a. Disconnect the RF generator from the 40dB pad while leaving the pad connected
to J1.
b. Set the scope amplitude for 50mV per division and the time base to 2ms per
division (should already be there). Leave the scope connected to J4.
c. Adjust the DC power supply to current limit at 200mA.
d. Adjust R13 to the 50% point.
e. Connect either a shorted plug to J3 (key jack) or the key.
f. Adjust C39 (transmit filter) for maximum voltage at the scope. This is at audio
frequency. Make sure C39 is not at either the minimum or maximum capacitance
setting.
g. Measure the DC current draw from the power supply which must be less than
200mA. What value was measured? ______________________
h. Adjust C34 (transmit frequency) for 575Hz +/- 10Hz as measured by the scope.
i. Set the scope amplitude for 2V per division and the time base to 200ns per
division and connect the scope to the transmitter end of the 40dB attenuator (not
the open end).
j. A 40dB pad reduces the power by what factor? ______________
k. Measure the RF voltage at the scope and convert to transmitter power
remembering that there is a 40dB pad prior to the scope. What is the measured
power? _____________
l. Remove the short on the plug connected to J3.
m. Adjust the DC power supply to current limit at 600mA.
n. Set the scope amplitude for 5V per division.
o. For the next step the transmitter will be run at maximum power so do not key the
transmitter for more than 10 seconds continuously.
p. Adjust R13 fully clockwise, short the plug at J3 or use the key, and quickly
measure the RF voltage on the scope. Quickly remove the short and set R13 to
the 50% point.
q. Using the just measured voltage what is the maximum power the transmitter can
provide? _____________
This completes the Norcal 40A calibration!