- C1, C4 e C9 = .01uF, 63V
- C2 = 47uF, 16V
- XCC3, C8 @ 45 Ohms cada um
- XCC5 @ 750 Ohms
- XCC6 + C7 @ 200 Ohms
- XLL1 @ 260 Ohms
- XLL2 @ 4500 Ohms
- R1 = 100 Ohms 1/4 Watt
- R2 = 100K 1/4 Watt
- R3 = 100 Ohms 1/4 Watt
- D1 = 1N4148
VFO
For me, the VFO is the
most important circuit in a transceiver.
Many circuits have been tested, but the above one has given me
the best results, mainly a very good stability.
A piece of PVC tube, the one used in electrical installations,
has been used as the support of coil L1.
Coil L2 is an RF choke with about 100 uH or more, it is frequency
dependent. Best results obtained with the value shown in the
components description shown above.
Q1 is MPF102 but others can be used.
Capacitors C3, C5, C6 e C8 are
polystyrene. It is a good practice to use two or more capacitors
in place of C6 to increase thermal
stability.
C7 must also be a series /parallel
arrangement, it depends on its value, the working frequency and
the wanted ratio.
D1 is used to limit positive
oscillations.
A power supply with any value between 5 and 9 volts and a high
degree of regulation, in order to avoid slipping, can be
used.
A VARICAP circuit is being used in place
of C7. No changes have been noted in
stability, mainly after the initial ten minutes.
A buffer amplifier must be used at the output of the VFO in order
to avoid that it is overloaded. The circuit below can be
used.
