"Jim, N2VX" ) writes:
On Fri, 19 Dec 2003 22:11:23 -0000, "Richard"
wrote:

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

With digital readout, though I suppose I could just hook up a simple a
frequency counter to read frequency.

TIA. Rich.


If you want to do DX'ing get an existing receiver and put in a
narrower filter. Many of the older tuners are ideal for this. I saw
writeups on this in magazines over 20 years ago and don't remember
what bandwidth filter was recommended.

An interesting project would be mods to the GE SuperRadio II or III.
They are cheap, available and have a tuned RF stage.

73,
Jim

That's a bit misleading. Most FM BCB receivers, now and in the past,
have an RF stage ahead of the mixer, and it is tuned. I once had
a nice Sony stereo receiver that worked well on FM, and it's lack of
an amplifer ahead of the mixer was pretty uncommon (and likely accounted
for it's good overload resistance).

The "TRF" stage in a Superradio is in reference to the AM band,
where in non-car radios, an RF stage is an exception.

Also, while it does seem a bit of work has been done in the design
for better AM reception, that RF stage and the better than average
loopstick, it does not seem like the FM section is anything to write
home about. I gather it's a fairly generic design.

This is part of the mythology of the Superradio. It's not all that
great, just maybe a little bit better than the average portable or
table radio, but people point to it when the concept of "a better
radio" comes up. Once you start spending the money, better to spend it
on a better design. Or better, buy a car radio that will have good
reception, or some used stereo that did have a bit of extra care in it's
design, so it actually won't overload in an urban environment.

Michael VE2BVW

Doug Smith W9WI wrote:
edges of the channel. If the receiver's filter is too narrow to pass
that, the signal peaks will be chopped off, resulting in severe
interference.

Oops. That should have read "...severe *distortion*."

--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

Doug Smith W9WI wrote:
edges of the channel. If the receiver's filter is too narrow to pass
that, the signal peaks will be chopped off, resulting in severe
interference.

Oops. That should have read "...severe *distortion*."

--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

"Jim, N2VX" wrote in message
news

An interesting project would be mods to the GE SuperRadio II or III.
They are cheap, available and have a tuned RF stage.

And an essentially uncalibrated frequency dial. Pretty bad for DXing IMO.

Almost any digitally-tuned car radio would be better for DXing. Remember
that cars drive through all the worst reception areas and their radios have
to at least try to work there.

"Jim, N2VX" wrote in message
news

An interesting project would be mods to the GE SuperRadio II or III.
They are cheap, available and have a tuned RF stage.

And an essentially uncalibrated frequency dial. Pretty bad for DXing IMO.

Almost any digitally-tuned car radio would be better for DXing. Remember
that cars drive through all the worst reception areas and their radios have
to at least try to work there.

In article ,
(Michael Black) writes:

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.

Going to www.KitsAndParts.com by Dieter Gentzow, W8DIZ,
you can find the old Motorola MC3362P (2 for $4) which is a
complete FM receiver IC. There's a full Motorola datasheet there
with application data. A one-IC FM receiver for headphones.

For some audio power output, he has National LM380s at 4 for $5.
For an RF preamp, he has Fairchild J310 J-FETs at 12 for $4.
There's also a respectable number of Micrometals toroid cores for
IF and RF filtering. Datasheets for all except a full info range on
the Micrometals cores (which some think are made by Amidon).
www.micrometals.com for full core information.

If the MC3362 is too much or too little, Dieter has 612 Gilbert cell
ICs for mixer-oscillator applications and MC1349 gain blocks (its a
slightly higher gain version of MC1350) for the IF.

A fairly good supplier of oldies but goodies in semiconductors and
toroid cores.

LHA
retired (from regular hours) electronic engineer person

In article ,
(Michael Black) writes:

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.

Going to www.KitsAndParts.com by Dieter Gentzow, W8DIZ,
you can find the old Motorola MC3362P (2 for $4) which is a
complete FM receiver IC. There's a full Motorola datasheet there
with application data. A one-IC FM receiver for headphones.

For some audio power output, he has National LM380s at 4 for $5.
For an RF preamp, he has Fairchild J310 J-FETs at 12 for $4.
There's also a respectable number of Micrometals toroid cores for
IF and RF filtering. Datasheets for all except a full info range on
the Micrometals cores (which some think are made by Amidon).
www.micrometals.com for full core information.

If the MC3362 is too much or too little, Dieter has 612 Gilbert cell
ICs for mixer-oscillator applications and MC1349 gain blocks (its a
slightly higher gain version of MC1350) for the IF.

A fairly good supplier of oldies but goodies in semiconductors and
toroid cores.

LHA
retired (from regular hours) electronic engineer person

Actually, they aren't much different than an AM design, except that
generally, you use quadrature detection for demodulation, and that you have
a deemphasis filter. The I.F. bandwidth is different, but pretty much
everything else is the same.

Pete

Richard wrote in message
...

"Pete KE9OA" wrote in message
...
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

I hear that FM RX's are pretty complicated affairs. Most FM DXers it seems
just modify commercial sets. Reduce bandwidth from say 230Khz to 110 Khz.
I
suppose that going this way has quite a lot of merit. Cheaper probably.

Actually, they aren't much different than an AM design, except that
generally, you use quadrature detection for demodulation, and that you have
a deemphasis filter. The I.F. bandwidth is different, but pretty much
everything else is the same.

Pete

Richard wrote in message
...

"Pete KE9OA" wrote in message
...
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

I hear that FM RX's are pretty complicated affairs. Most FM DXers it seems
just modify commercial sets. Reduce bandwidth from say 230Khz to 110 Khz.
I
suppose that going this way has quite a lot of merit. Cheaper probably.

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?