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

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?

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

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?

"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.

"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?

In article , "Richard"
writes:

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?

You need to refresh your personal databanks on basic modulation.

In FM the modulation amplitude "swings the frequency up and down
in frequency." [close and simplistic, there's a bit more to it...]
Limiting the bandwidth of the receiver is the same as clipping the
peaks of an amplitude modulation. You WILL get a LOT of
distortion on high-amplitude modulation input at a station.

In a limited-bandwidth AM receiver there is no limit on the amplitude
of an AM signal, just the frequency range of the modulation signal.

In a limited-bandwidth FM receiver there is both a limit on the
amplitude and frequency range of the modulation signal.

Len Anderson
retired (from regular hours) electronic engineer person

Richard wrote:
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.

Yes, you used the wrong termgrin.

"NBFM" has a specific technical meaning, IIRC a system where the
modulation index (ratio of peak deviation to maximum modulating
frequency) is less than 1.

For FM broadcast, the peak deviation is 75KHz and the maximum modulating
frequency 15KHz. (OK, I'm ignoring stereo...) So the modulation index
is 5.

For police radio, the peak deviation is roughly 3KHz and so is the
maximum modulating frequency. So the modulation index is 1.

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?

Lots of distortion.

In AM, distance from the center of the channel correlates to modulating
frequency. Restricting the filter bandwidth in the receiver restricts
the frequency response - the high audio frequencies ("treble") are
rolled off. But it has no effect on the range of *amplitudes* that can
be received; a loud sound within the bandpass of the filter will still
be reproduced accurately.

In FM, distance from the center of the channel correlates to modulating
*amplitude*. A loud sound will push the transmitted signal to the outer
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.

Remember that the 75KHz peak deviation for FM broadcast is 75KHz *either
side* of center. To get the actual bandwidth required you have to add
the peak modulating frequency to that. 165KHz, not counting stereo.

You can chop some of that off at the expense of some distortion. I've
found in practice, 110KHz filters work fine for DXing though I wouldn't
want to listen to a symphony through them. 75KHz would probably be
reasonably intelligible.
--
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

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