D. Alignment
1. DC check point
(1) Voltage across the zener diode VD3: 3.4 - 4.4 volt
(2) The bias of transistor V1: The voltage across R4 shall be 0.4 - 1 volt (potentiometer RP1 set to
maximum gain position, the Ic of V1 will be 0.4 - 1 mA)
The bias of transistor V2: The voltage across R10 shall be 1.5 - 3 volt (the Ic of V2 will be 1.5 - 3 mA)
The bias of V3: The voltage across R15 shall be 2 - 2.5 volt (Ic of V3 will be 2 - 2.5 mA)
Normally you don't have to adjust the bias, because the design can cover the variance of the
components.
2. Alignment of the variable local oscillator
(1) If you have a standard RF signal generator
(a) Set potentiometer to the center position;
(b) Set signal generator to 3.5 - 3.6 MHz, CW mode, higher output level. Connect the output
and the ground of the signal generate with a wire. Couple the wire to the magnetic antenna of
the receiver by winding the wire on one end of the magnetic rod for one turn;
(c) Change the output frequency of the signal generator in a wider range. A beating tone shall
be heard from the earphone, this means the local oscillator is working. Set the signal
generator to 3.55 MHz, then align the cap of the coil T2 (white) until the beating tone is heard
again;
(d) Turn potentiometer RP2, the signal of 3.5 MHz and 3.6 MHz all be received at two position
of RP2, which shall be near by the both extreme positions. If 3.6 MHz can not be heard but the
3.5 MHz can be heard at the RP2 position near by the center, please align the cap of T2
counter clock wise; or vise versa.
(e) If the receiving coverage is too wide, replace the R13 with greater value, or vise visa.
(2) If you use 80m fox transmitter
(a) Set potentiometer RP2 to the center position;
(b) Turn on the fox transmitter (3.55 or 3.54 MHz). Place the receiver close to the transmitter
antenna;
(c) Turn the cap of T2 until a beating tone is heard, fine tune it to make the tone nicely (about
1000Hz);
(d) Turn the potentiometer RP2, the signal from fox transmitters of 3.5 and 3.6 MHz shall be
both heard. If only one signal of 3.5 or 3.6 MHz can be received, please fine tune the cap of T2
(see the previous section);
(e) If the receiving coverage is too wide, replace R13 with a greater value, or vise versa.
3. Alignment of antenna tank
Receive a signal of 3.53 MHz from a signal generator or transmitter. Fine tune capacitor CT to peak
the tone. If no peak can be obtained, change the position of the coil on the magnetic rod, then fine
tune CT again.
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