4SQRP Bayou Jumper 40 Meter CW Transceiver, Assembly & Instruction Manual

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revised 3 Feb 2021 Bayou Jumper revB Assembly Manual page 40 of 46
D. Routing wires to the main PCB for installations of mods or accessories.
Since there is room under the main PCB as installed in the recommended box, the possibility
of adding accessories such as an audio filter, sidetone oscillator, keyer,
etc , are certainly
attractive.
Several “wireways” – pre-drilled ¼” holes in the circuit board – have been provided
to allow for passing wires from above and below the main board. The holes are isolated from
the top and bottom ground planes.
E. Tuning Range
An easy way to change the tuning range is to change the value of R5. Smaller resistance will
increase the range, while larger resistance will decrease it. The downside of increasing the
range is that the tuning will become more non-linear
– tuning faster at the lower end of the
band. R5 should not be decreased below about 5 to 10 k or so.
A pair of pads, designated
R5a , have been provided. They are shorted
across with a thin trace on the bottom of the PCB that must be cut if
R5a is to be used. Inserting extra resistance, or better still, a
potentiometer, at R5a will move the bottom of the tuning range up in
frequency, while leaving the upper end virtually unchanged. So if most
of the use of the radio were going to be in the 7100 to 7125 kHz
region, it could be spread out over nearly the full travel of the main
tuning control. But the range could be easily restored to cover the lower part of the band.
A potentiometer at
R5a does act rather like a fine tuning control, but its effect is greatest at
the low end of the range, diminishing to no effect at all at the top end.
F. PCB footprints for optional additional components (not supplied in the kit)
Mounting pads and connection points have been provided for an additional potentiometer (of
the same physical type as the others in the kit) and a miniature SPDT toggle switch. Adjacent
to each are a set of pads that can be used to make wire connection to the parts.
Possible uses for the potentiometer could be a fine tuning control, a keyer speed control, a
sidetone pitch or level control. Bourns 9 mm pots, series PTV09A, 25 mm shafts, will fit the
footprint.
The SPDT switch could switch an audio filter in or out, or select resistors at R5a to change
the tuning range. Marlin P Jones # 25010SW (ON-OFF-ON), or similar, fits the footprint.
On the underside of the front panel are centering marks to allow drilling a hole properly
positioned for these optional parts.
A pair of pads are provided for an optional capacitor,
C33 , to be installed across the feedback
resistor of the audio amplifier IC. A few hundred pF has been found to “mellow’ the audio
sound of the receiver. The larger the capacitance the more the highs are suppressed.
CUT HERE