On 28 Jul 2003 07:13:56 GMT, (Michael Black)
wrote:

John Crighton ) writes:
Maybe rob some 455 KHz IF coils out of a dud
transistor radio if necessary. Save some dosh.

It would be interesting to have some tests done on the original
receiver. If I remember the start of the thread, the receiver
is not sensitive enough. I can't help but wonder if it's insensitive
or it's too sensitive, leading to overload in the front end.
That would be just as bad (in terms of operational range) as an insensitive
receiver.

Likewise, if one had an idea of the IF bandwidth, it would be easier
to know if the problem really needs fixing, or there is some other
issue. If the thing is using some sort of ceramic filter, looking
at the board would hopefully say what type (unless the markings have
been sanded off), and then the specs could be found. Assuming it's
a standard IF frequency, maybe one could find a narrower filter
that would drop right in. For all we know, it may have too wide
an IF, and that's causing the initial problem.

Knowing the bandwidth of the existing filter would also make it
easier to figure out a complete replacement for the receiver.
In this day and age, ceramic or crystal filters are the way to go,
not a bunch of IF transformers. Pull parts out of a cordless phone,
at least the 49MHz type, and you'll get a filter suitable for
narrow deviation FM and a crystal for converting from 10.7MHz
to 455KHz. If FM happens to be the operating mode, then pull
out the whole IF strip. If that filter is too wide, pull the
455KHz ceramic filter out of a am BCB radio, or for something
narrower, a CB set. The possibilities are endless.

Michael VE2BVW


Hello Michael,
you are correct, there are many possibilities. I would
like him to do some tests also.

The main stumbling block for Paul is no information
on the present Sanwa receiver and an understandable
reluctance to poke around and then kill it
accidentally, especially if it is borrowed or belongs
to a mate.

I suggested building a new Rx that is physically big
so that experiments and mods are easily done by
Paul. If the CRO probe slips.....no big deal. :-)

We know of this LM1872
http://www.ife.tugraz.at/datashts/nsc/h7912.pdf
that we can all look at and help out with suggestions.
Do you know of anything else we can all see on a
website?

Regards,
John Crighton
Sydney