No, it is not particularly difficult to build for 144/432 MHz.
All you need are good low-noise devices, short leads and a little
determination, which I'm sure you have plenty of. For starters,
why not have a look at the simple 144 to 30MHz converter on this
site -


http://homepage.tinet.ie/~ei9gq/vhf_conv.html
Thanks for the link. Something lil' more complex ?

This should give you an idea of the style of construction
needed. The only component that you may have trouble with is the
overtone crystal but there are other ways of achieving the same
end.
We got good crystal producer here in Poland called Omig, BTW they are
IBM supplier I think I'll find something.

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

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

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

Richard


Julian Vereker wrote in message
om...
Hello,

I'm trying to find some simple receiver (or at least a converter)
project for 440 or 144 MHz to build. I'm interested in CW mode. But
there's nothing.
Is it very hard to build something for 70 cm or there are another
reasons, that I can't find anything?

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

Richard


Julian Vereker wrote in message
om...
Hello,

I'm trying to find some simple receiver (or at least a converter)
project for 440 or 144 MHz to build. I'm interested in CW mode. But
there's nothing.
Is it very hard to build something for 70 cm or there are another
reasons, that I can't find anything?