Ramsey Electronics HR30 Instruction Manual - page 21
HR30
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21
If you want the opposite of bandspread (that is as MUCH frequency range as
possible over full rotation of the tuning knob ) increase the value of C4. This
will cause the varactor diode to have greater effect on the tuning. Try values of
33pF up to 100 pf.
FREQUENCY STABILITY:
A kilohertz of drift is not a big deal in FM circuits or a shortwave broadcast
configuration, but ANY frequency instability is annoying when trying to receive
CW or SSB. The varactor - controlled Local Oscillator is indeed a VFO, and
therefore needs all the consideration given to any VFO circuit. Even though
this tunable oscillator design takes good advantage of the SA602’s capabilities
and offers nice tuning range from a simple varactor circuit, we do not
represent it as suitable for transmitter frequency control or for demanding
receiver applications. In any ham VFO design, ANY unshielded or
uncompensated oscillator components are susceptible to the influences of
temperature change and of nearby moving objects. The use of a suitable
enclosure and secure mounting of the PC board within that enclosure will
maximize the stability of the oscillator. One to two KHz of slow drift may be
expected as components warm to operating temperature; after that the
oscillator is reasonably stable
OTHER METHODS OF DIAL CALIBRATION:
A easy way of making your own dial is to paste a small rectangle of paper
behind the tuning dial knob. Then as you tune in different frequencies, pencil
in on the paper the received frequency. Or a simple logging scale may be
affixed behind the tuning knob on the front panel. A logging scale is simply a
set of numbers for adjusting a control. For example, 4 might represent
10.100MHz and 5.5 being 10.103Mhz, and so forth.
DIRECT FREQUENCY READOUT:
A novel advantage of the simple direct conversion receiver is that a general
purpose frequency counter may be used to give a direct readout of the
oscillator frequency. While you could experiment with an RF pickup loop or
tuned circuit and counter preamplifier to boost the oscillator’s tiny output to a
level suitable for the counter, the most reliable method is to wire a high-
impedance counter probe line directly to pin 7 of the SA602, 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:
With the RF gain turned all the way up , it may be possible to hear the