On Sun, 21 Dec 2003 20:34:13 +0800, "Richard Hosking"
wrote:

For CW you need a tunable VFO and this is not easy with reasonable stability
You wiull have to use an HF transceiver as a tunable IF

If you are _only_ interested in the 2m CW band around 144.050 MHz, a
VXO should give a sufficient tuning range.

A fundamental mode crystal (i.e. below 20 MHz) can be tuned by
500-1000 ppm with a series inductance and variable capacitor. This
should give a 70-150 kHz tuning range on the 2m band.

If a 10.7 MHz IF with low side injection is used, the required LO
frequency would be about 133 MHz is needed, which can be done with a
14.82 Mhz crystal and two triplers or with 16.67 MHz crystal and three
triplers. High side injection should also be checked, since these may
give crystal frequencies that are easier to obtain.

These days the doublers and triplers can be quite easily implemented
with MMICs (such as MAR-x series) and bandpass sections between the
stages.

MMIC:s have reasonable noise figures for the 2m band even as RF front
end amplifiers, but sufficient front end selectivity is often required
to avoid overload problems if the gain is very high.

Paul OH3LWR