/ NorCal 40A - Modification for 30 Meters
The 40A is designed and
sold as single band 40 meter CW transceiver, but it is possible to modify
it for other bands.
Here are the component changes
needed to put the 40A on the 30 meter band. Note that since you are converting
to a higher frequency, the existing wire on the toroid inductors can be rewound
with fewer turns.
- Replace all six crystals, X1 to X6,
with 8 MHz crystals. It is desirable to use a matched set of crystals (within
20 Hz), and to use the four closest matched ones for X1 to X4, the receiver
IF bandpass filter.
- Replace L1 with a 10uH fixed inductor.
- Rewind T3 with 21 turns on the primary
and 6 turns on the secondary.
- Replace C6 with 39 pF capacitor.
- Rewind L6 with 24 turns.
- Rewind L7 with 13 turns.
- Rewind L8 with 14 turns.
- Replace C45 and C47 with 270 pF capacitors.
- Replace C46 with 560 pF capacitor.
The VFO will stay at 2.1
MHz. You may need to tweak the turns of L9, the VFO inductor, slightly to
achieve the desired VFO tuning range of 2.1 to 2.15 MHz.
Note that this is not an
authorized Wilderness Radio modification. You do this mod at your own risk.
Although the component values listed above worked for me, there is no guarantee
that they will work for you.
Other 40A modifications:
- 10 turn tuning pot: Highly recommenced
along with the KC-1 counter/keyer module.
- Reduced tuning range: Since most
CW operation is below 10.140 MHz, you may desire to restrict the tuning range.
This can be done by placing a resistor at the junction of R19 and the VFO
tuning potentiometer to ground. I used a 20K resistor to tune 10.100 to about
10.140 MHz. You can experiment with this value to suit your preference.
- Reduced transmitter self-oscillations:
Slip a ferrite bead on the base lead of the driver transistor Q6. Also, parallel
another 100 Ohm resistor across R14, the PA base resistor. This last step
will slightly reduce the power output, but will improve the amplifier stability
caused by antenna mismatch or a "too high" setting of R13, the drive
- A little more power: Replace
Q5 with a J310. I got .1 watt increase at 30 meters.
- Faster AGC action: Replace C29
with 1uF tantalum capacitor.
- Reduce maximum keyer speed: Replace
C1 (on the KC-1 board) with .047 uF capacitor.
- Reduce CW clicks and thumps when
the frequency counter is operated: Add a 1 K resistor between the KC-1
mute connection and the 40A mute input at the junction of D1 and D2.
- Reduced KC-1 audio level: Add
a 330 K resistor between KC-1 audio output and 40A audio amplifier input U3,
to WØCH Home Page
Page issued May 30, 2007