I was thinking about going with a high level mixer, something with an IP3 in
the +30dBm range. I would probably make it a double conversion unit. This
way, I could use a bandpass filter at the front end.
You are right, though.................there are quite a few good performers
already on the market, and those auto radios are no exception. The newer
ones that use the Philips dual conversion chipset are very good on the AM
broadcast band, too.

Pete

Michael Black wrote in message
...
"Pete KE9OA" ) writes:
It wouldn't be quite the same. You would be clipping the sidebands, and
experience quite a bit of distortion. A 110kHz filter is about as narrow
as
you can go.
I've been meaning to come up with a tuner that would be in the class of
a
McIntosh MR78 for the past couple of years, but something has always
come
up. Maybe after my current project, I will do this, if there is enough
interest.

Pete

For most people, it makes more sense to simply change the filters
in an existing FM BCB receiver than start from scratch. Indeed,
it seems to be a relatively common practice among people who DX
that band.

Not that building something from scratch wouldn't be interesing,
only that if "narrow bandwidth" is all that's wanted, then there's
no sense in building it all. And there isn't much sense in putting
narrow filters in a mediocre homebuilt FM receiver, which is the
sort of thing you see in construction articles.

I use Delco digitally tuned car radios as my "table radios", running
them off power supplies. For the price, a few dollars at garage sales,
they are pretty good receivers on the FM band. I know it would benefit
from a narrow filter for a few stations I like to listen to. But of
course,
a lot of FM receivers aren't that great for distant reception, being too
sensitive, without good overload protection.

In some cases, it might be intriguing to build a single channel FM
BCB receiver. Build it like a ham band converter, with plenty of
tuned circuits at the fronte end, little or no RF amplification,
and a good mixer. Being fixed tuned, one could optimize it for
that frequency, and not worry about tracking, or the problems of
ganging a number of tuned circuits. For the local oscillator, one
could go with a crystal oscillator chain.

Michael VE2BVW


Richard wrote in message
...
Dr. A.T. Squeegee wrote:
In article ,
says...

Hi. Anybody developed a nbfm RX project covering the FM band (appx
87.5Mhz-108Mhx).

NBFM? As in narrow band?

What would be the point? Here in the U.S. at least, that entire
band is assigned to FM broadcasting, and it is anything but
narrow-band.
Typical deviation from a broadcast station is 75+ kHz.


Maybe I used the wrong term. I think lots of HiFi tuners have very wide
filters much greater than 75 Khz. For DXing it seems then you need no
more
than say 75Khz. A tuner with that bandwidth would, in a sense,
(Ithink)
compared to a regular HiFi tuneer be a narrow bandwidth tuner.

BTW, what would be the result if you used say a 20Khz filter on a FM
signal
with 75 Khz deviation? Would you get distortion or a perfectly copyable
signal. I mean is it the analagous to using a 2Khz filter for an AM
signal
transmitted at 6Khz wide?