Ramsey Electronics HR-80 Instruction Manual page 22

method is to wire a high-impedance counter probe line directly to pin
7 of the NE602, terminated to a rear panel frequency counter
connection of your choice. This will consist of a short piece of mini-
coax to a 1 megohm resistor bridged by a 27 to 33pF capacitor as
shown below:
NE60
2
PIN
7
With the RF gain turned all the way up , it may be possible to hear
the counter's busy humming action in the background, but not to a
serious degree. It drops out with a slight reduction of the RF gain. If
you decided to add such a counter connection to your receiver,
remember that the coax as well as the coupling capacitor become
part of the oscillator circuit. Make the coaxial cable connecting the
counter to the receiver as short as possible. You will experience a
frequency change of several KHz when connecting or disconnecting
the counter. Also, this additional capacitance in the oscillator circuit
reduces the tuning range to approximately 100KHz, thus offering
another way of getting bandspread for your favorite frequencies.
Finally, it may be necessary to operate the counter on battery power
only; connection of an AC adapter might introduce considerable hum
into the receiver.
THE LM386 AUDIO OUTPUT:
As already mentioned the LM386 is certainly capable of far more
audio power output than is given in this basic receiver circuit. It can
only boost what it gets directly from the NE602. There is certainly
space on the HR-80 circuit board to install an audio preamplifier (i.e.
2N3904, or minimum-gain LM386) in the circuit trace between C8,
the audiocoupling capacitor from pin 4 of the NE602 to the volume
control. The following is an audio preamplifier idea submitted by one
of our customers. Ramsey Electronics in no way warrants that this
27
pF
1
MEGOH
M
HR-80• 22
TO
COUNT
ER