ELEC 432
In the Lab II: Assembly & Testing
Assembly
Except for a
greater number and variety of components,
assembly of this circuit should be a repeat of what you did
in Exercise 2.
A couple of things to watch out for:
Be sure to install all of your jumper wires.
The power connector must be installed on the
bottom
of the board.
Also, the circuit is also more complex than that in Exercise 2.
You should assemble and test it in sections, as described below.
Testing
Since this is a proven design, it should work correctly,
assuming your layout and assembly are correct.
However, even a single mistake can render the circuit
completely inoperative, with no indication of the root cause.
To make such mistakes easier to find, it's a good idea
to test your circuit in sections as you assemble it.
For this circuit a good assembly/test sequence would be:
-
Install the
connectors,
bypass capacitors,
and
bias networks (R1, R2, C23, C24 and R3, R4, C25).
Verify the correct DC voltages at the IC power pins
and the two bias points
(transformer center tap and flip-flop clock).
-
Set the signal generator frequency to
40 MHz and connect its output to
LOin.
Verify that the clock to the 74AC74 is a sinusoid
centered about 2.5 V.
Increase the signal generator output level
until this waveform has a 5 V p-p amplitude.
-
Install the 74AC74.
Verify that
ILO
and
QLO
are square waves at 1/4 the frequency of
LOin
and 90° apart in phase.
-
Install U1.
Connect
IFin
to a
1 V p-p, 5 kHz sine wave.
Verify that
V1
and
V4
form an appropriate differential signal pair.
Similarly, install U2 and verify
V2
and
V3.
-
Install the remaining components
(C17-20, U3, and T1).
Examine
RFout
with both the oscilloscope and the spectrum analyzer.
After convincing yourself that the observed signal is
correct in both the time and frequency domains,
declare victory and
proceed to the appropriate celebration.
There are other possible sequences.
If you don't like this one, you can make up your own.