Ramsey Electronics HR30 Instruction Manual - page 20
HR30
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For instance, if you choose a DC power source other than the 9-volt battery, the
space allowed for the battery offers plenty of room for a top mounted perfboard
or PC-board for preamp stages and or any sort of passive or active audio filter
that suits your needs. Keep your work neat with short leads so as not to
introduce broadcast station overload.
ALTERNATE POWER SOURCES:
Most of the HR30 circuitry can be operated from 6 to 14 volts without damage
or significant modification. However, it is quite important that you carefully hook
up with the correct polarity; reverse polarity or excessive voltages WILL
damage your kit.
BANDSPREAD AND TUNING RANGE:
The easiest way to enjoy finer tuning , if you plan to use your receiver only for
checking your favorite segment of the band, is to adjust the oscillator coil so
that your desired segment falls within the second half of the rotation range of
the tuning control. The first half of the rotation range covers about 70% of the
actual tuning in KHz, while the other 30% is spread over the other half of the
rotation range. If your interest is in monitoring SSB, the normal alignment will
work fine. For optimum CW only listening, set the lower band edge with the
tuning control in the 12:00 position of its range.
In planning any ‘bandspread’ improvement, it is useful to understand exactly
how varactor tuning works. The control level varies the amount of DC voltage
applied to the diode. The highest produces the lowest capacitance, while the
lowest voltage yields the highest capacitance. The spread is typically about 30
to 40 pf. from minimum to maximum.The goal in achieving bandspread or ‘fine -
tuning’ is to achieve a smaller variation in capacitance with the comfortable
tuning of a knob.
Any resistor in a range from 500 ohms to 3000 ohms, connected in series with
the ground lead of R2, will set a limiting effect on varactor capacitance range
and therefore create a “bandspread “ effect. The higher the resistance value,
the shorter the available tuning range.
If you wish to reduce the tuning range of R2 down to 40 or 30KHz or even less,
for a favorite band segment or calling frequency, reducing the value of C4 will
decrease the capacitance effect of the varactor diode, D1. Values from 2 to 5pF
may give you exactly the tuning range you are looking for.
If you are using your own enclosure and have room for a separate fine tuning
control, one useful choice is a 250 ohm speaker attenuation rheostat (Radio
Shack model no. 271-265) wired in series with either outside ‘leg’ of the main
tuning control. Such a control can make fine adjustments to a CW signal so the
tone is pleasant and smooth sounding.