SR2
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22
reception. Eventually, you will get a clue as to what general frequency band
you are hearing, because many stations periodically announce their
frequencies, particularly at sign-on and sign-off times.
If you like precision, use a frequency counter or calibrated receiver to find
the SR2's strong oscillator signal, remembering that there is a 455 KHz IF
difference (above or below) between the local oscillator frequency and the
broadcast signal you are hearing.
TROUBLESHOOTING TIPS
If you experience difficulty, think of your SR2 in its several sections or
stages: oscillator-mixer, IF audio and AGC, and final audio output (LM386).
The first step in case of problems is to make sure that the tunable oscillator
is working, which can be done by listening for its signal on another receiver.
After the oscillator circuit is confirmed working, standard signal tracing
procedures should isolate any problem, which will be either an incorrectly-
installed part, a defective part or a bad solder connection. Correct
orientation or polarity of all diodes, transistors, electrolytic capacitors and
ICs is essential.
PROBLEM:
Strong shortwave broadcast audible throughout tuning range
SOLUTION:
This can occur if your antenna is "too good" or if the RF Gain
control is turned up too high. The high sensitivity of the front end is designed
for simple antennas, with most reception quite satisfactory with only 25 feet
or so of wire.
PROBLEM:
Local AM radio station audible throughout tuning range
SOLUTION:
Whether this will even happen depends on how close you are
to a local AM station. It is very important that all component leads be as
short as possible, since just a bit of wire can help D1 and the several stages
of audio amplification give you a free, unwanted "classic crystal radio". A
grounded metal case for the SR2 is one possible solution.
