xpyttl wrote:

"Fred McKenzie" wrote in message
...


Converting a modern frequency-synthesized radio to receive different
frequencies may be possible, but quite a neat trick.


Actually, in theory it is pretty easy, in practice, darned near impossible.
Given that the railroad and 2 meters are neither very far from the weather
band, you probably could get reasonable performance without any front end
changes.

I had a Nissan/Clarion radio that was stock for models exported to the
"English Caribbean". It was set for 9 kc AM-BC channels and had no
switch as an option. No importa that the Caribbean doesn't use 9kc
channel spacing. The switch placement markings were on the multi-use PCB
but it wasn't there. I'm sure there was a workaround but without
supporting documentation it wasn't to be done...at least not by me.

In the case of the Weather Band....since there is more than one freq in
use, do you have any channel option there (WX1 or WX2) or is it just so
broad that it will receive any Wx-band channels?

I also suspect that this LO freq is programmed into the chip. They
don't really make them "hobbyist-friendly" do they?

-Bill




in the old days that tuning knob was attached to
a variable capacitor and a slight change in the L and C values could move
the radio. Today, however, that knob is attached to an encoder that is read
by a microprocessor. The micro then tells a synthesizer what frequency to
make. So, it is a simple matter of reprogramming the micro.

There's the rub. Even if you had the capability to reprogram the micro
(really not all that unreasonable) you would need to get the source code
(not bloody likely). And if you had the code, simply understanding it would
be a major challenge; I was visiting one auto manufacturer a few months ago
and was surprised to learn they have over a million lines of code in the
radio!


A simpler approach would be to buy or build an external tuner. It could
be crystal-controlled, switching between crystals for different
frequencies. It could use only one crystal and use the existing radio's
tuner to select different frequencies.


This, actually, could be pretty simple. You are only a couple MHz away from
the railroad frequency, so some sort of front end filter, a 602 with an
appropriate crystal, and a whopping attenuator on the output of the 602 and
you should be good to go. You could do something similar for a repeater,
the rock would be more like 20 MHz instead of 2, but you couldn't cover much
of the 2 meter band with the tuning from the weather band. But for one
repeater...

The ugliest part would be switching it in and out if you wanted to listen to
the FM Broadcast band.

..