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.

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.


--
Dr. Anton Squeegee, Director, Dutch Surrealist Plumbing Institute
(Known to some as Bruce Lane, KC7GR)
kyrrin a/t bluefeathertech d-o=t c&o&m
Motorola Radio Programming & Service Available -
http://www.bluefeathertech.com/rf.html
"Quando Omni Flunkus Moritati" (Red Green)

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?

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

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.

Richard wrote:
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.

It's certainly the most bang for the buck. Really, a good FM receiver
isn't much more complicated than a good AM receiver -- but a
bare-bones-just-barely-receives-the-strongest-stations FM receiver is
quite a bit more complicated than a bare-bones-..... AM set.

Usually you can reduce the bandwidth of a FM receiver by simply removing
the monolithic ceramic filters and replacing them. I've done that on my
Technics ST-G50; at my location 30 miles outside Nashville, I have
received at least one DX station on every frequency that doesn't have a
local. (yes, that includes the frequencies adjacent to 100,000-watt
locals)

Forget what I paid for the filters - it was definitely less than $5
apiece. My tuner needed two.

=============================

Regarding going to 20KHz bandwidth...

In DX situations with heavy interference, a very narrow bandwidth might
be helpful for identifying DX stations. The programming will be mostly
unintelligible in a 20KHz bandwidth, but maybe it'll be more
intelligible than it would be against the interference from adjacent
channels in a more reasonable bandwidth.

I occasionally use the narrow filters in my TH-F6 HT to DX television
audio. Nobody would dream of listening to that audio for entertainment
but one can identify things they'd never ID on a TV set.

Don't know anyone who's tried putting a 10.7MHz IF 20KHz or similar
bandwidth filter in a FM broadcast tuner. You'd want it to be one of
multiple bandwidths, so you could select something more reasonable for
stronger signals.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

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.

Richard wrote:
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.

It's certainly the most bang for the buck. Really, a good FM receiver
isn't much more complicated than a good AM receiver -- but a
bare-bones-just-barely-receives-the-strongest-stations FM receiver is
quite a bit more complicated than a bare-bones-..... AM set.

Usually you can reduce the bandwidth of a FM receiver by simply removing
the monolithic ceramic filters and replacing them. I've done that on my
Technics ST-G50; at my location 30 miles outside Nashville, I have
received at least one DX station on every frequency that doesn't have a
local. (yes, that includes the frequencies adjacent to 100,000-watt
locals)

Forget what I paid for the filters - it was definitely less than $5
apiece. My tuner needed two.

=============================

Regarding going to 20KHz bandwidth...

In DX situations with heavy interference, a very narrow bandwidth might
be helpful for identifying DX stations. The programming will be mostly
unintelligible in a 20KHz bandwidth, but maybe it'll be more
intelligible than it would be against the interference from adjacent
channels in a more reasonable bandwidth.

I occasionally use the narrow filters in my TH-F6 HT to DX television
audio. Nobody would dream of listening to that audio for entertainment
but one can identify things they'd never ID on a TV set.

Don't know anyone who's tried putting a 10.7MHz IF 20KHz or similar
bandwidth filter in a FM broadcast tuner. You'd want it to be one of
multiple bandwidths, so you could select something more reasonable for
stronger signals.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

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.

"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?