Topics

BFM Spectrum


Charles Strickland
 

Can the BFM Spectrum fill be turned on/off?  Fill is considered a distraction by engineering types.


rmrrgs
 

Apologize for ignorance, but what
please is a BFM Spectrum ?

B. 


Calder Latham
 

Broadcast Frequency Modulation

On 12/30/2020 15:48, rmrrgs wrote:
Apologize for ignorance, but what
please is a BFM Spectrum ?

B. 
-- 
All the Best from
the woods of Maine.


George Stein - NJ3H
 

Greetings,

I found out what my problem was.  I had WFM selected instead of BFM.

I wanted to see the 19 khz pilot tone used by broadcast FM stations that are broadcasting in stereo.

If you go to Receive/Broadcast FM/Spectrum a spectrum window pops up indicating the components of the signal.  Hitting the button with a circle on it near the upper left of that window turns on the spectrum itself.

Happy New Year!

Regards,
George, NJ3H
Redmond, Oregon USA



On Wednesday, December 30, 2020, 12:48:44 PM PST, rmrrgs <rgsrose@...> wrote:


Apologize for ignorance, but what
please is a BFM Spectrum ?

B. 


jdow
 

The next interesting question is whether Simon's implementation can handle a station with RDS that is transmitting mono rather than stereo so there is no 19 kHz pilot tone. I notice the RDS specification contemplates this. But I rather suspect the number of stations actually doing this can underwhelm somebody who counts on the fingers of one hand.

{o.o}

On 20201230 13:11:34, George Stein - NJ3H via groups.io wrote:
Greetings,

I found out what my problem was.  I had WFM selected instead of BFM.

I wanted to see the 19 khz pilot tone used by broadcast FM stations that are broadcasting in stereo.

If you go to Receive/Broadcast FM/Spectrum a spectrum window pops up indicating the components of the signal.  Hitting the button with a circle on it near the upper left of that window turns on the spectrum itself.

Happy New Year!

Regards,
George, NJ3H
Redmond, Oregon USA



On Wednesday, December 30, 2020, 12:48:44 PM PST, rmrrgs <rgsrose@...> wrote:


Apologize for ignorance, but what
please is a BFM Spectrum ?

B. 


kb3cs
 

U.S. major market (very large city) news & information stations do this. i discovered this the first time i was experimenting with decoding RBDS myself and following along in the specification document i got my hands on where it said use the 3rd harmonic of the 19 kHz pilot tone (!!).  but .. but .. i could clearly see the 57 kHz subcarrier and no 19 kHz ..   :-P

a week later i (figuratively) banged on the office door of a different station's engineer until they too noticed the subcarrier injection level of their 67 kHz reading service for the visually impaired was way too low and the service was therefore extremely noisy (program barely audible). i was dismissed on the first attempt to call their attention to the problem ("thank you for your interest" email), and later found a historical record of their MPX spectrum clearly indicating a 67 kHz subcarrier well above the noise floor. it took a further few days until magically the subcarrier level looked the same as it had a few years earlier.

  -73 C (-99 F)


On Wed, Dec 30, 2020 at 01:33 PM, jdow wrote:
The next interesting question is whether Simon's implementation can handle a station with RDS that is transmitting mono rather than stereo so there is no 19 kHz pilot tone. I notice the RDS specification contemplates this. But I rather suspect the number of stations actually doing this can underwhelm somebody who counts on the fingers of one hand.

{o.o}
[...]


jdow
 

Most of the time the 19 kHz subcarrier is invisible unless the Big Voices and Big Noise er Music stop briefly. Then they are in your face. Of course, that depends on the station being properly setup. A Q 500 IIR filter for the pilot tone makes it easier to work with it. Was that station transmitting pure MONO?

If I had to get the attention of a local station with a screwed up signal I'd try documenting it with spectrum pictures that should show the subcarrier signals and don't. When a person talking takes a long breath of air you can get a good picture if  you are lucky. The second letter would suggest the FCC might find their signal error might be interesting when they audit the station come license renewal time. That feels sort of mean to do to them. But, it could save them their license. (All correspondence must be available at the stations for public review; and, the FCC specifically includes them in that "public.")

Of course, getting mean is not always politic. I love KUSC. They are no ads public pledge funded. So they work on shoestrings. And their RDS subsystem is somewhat dorked up and apparently difficult to use. So it's all screwed up from time to time. But, I don't want to do ANYTHING to jeopardize their license.

{^_^}

On 20210214 07:51:37, kb3cs wrote:
U.S. major market (very large city) news & information stations do this. i discovered this the first time i was experimenting with decoding RBDS myself and following along in the specification document i got my hands on where it said use the 3rd harmonic of the 19 kHz pilot tone (!!).  but .. but .. i could clearly see the 57 kHz subcarrier and no 19 kHz ..   :-P

a week later i (figuratively) banged on the office door of a different station's engineer until they too noticed the subcarrier injection level of their 67 kHz reading service for the visually impaired was way too low and the service was therefore extremely noisy (program barely audible). i was dismissed on the first attempt to call their attention to the problem ("thank you for your interest" email), and later found a historical record of their MPX spectrum clearly indicating a 67 kHz subcarrier well above the noise floor. it took a further few days until magically the subcarrier level looked the same as it had a few years earlier.

  -73 C (-99 F)


On Wed, Dec 30, 2020 at 01:33 PM, jdow wrote:
The next interesting question is whether Simon's implementation can handle a station with RDS that is transmitting mono rather than stereo so there is no 19 kHz pilot tone. I notice the RDS specification contemplates this. But I rather suspect the number of stations actually doing this can underwhelm somebody who counts on the fingers of one hand.

{o.o}
[...]


kb3cs
 

the 19 kHz pilot tone is visually obvious and rarely observed less than 20 dB above the MPX spectrum floor.
none o'yer fancy filterin' needed, can just eyeball it if yer glasses didn't get too dirty.

yes, jdow, really and for true, the FM station observed sent nothing but PURE FREAKIN' MONO. mainly to extend their service region.
Mono plus the RBDS subcarrier to make all those consumer radio text readouts say useful things about which type program is being broadcast on each segment of the hour.

i learned my mistake was to contact the second Stereo+subcarrier (non-mono) broadcaster's technical personnel using only words and numbers.

the second time i included annotated IMAGES of the 'before' and 'after' MPX spectrum and short to-the-point paragraphs.   :-P

i also clued-in the sponsor of the visually impaired reading service the following week.

at no time did i reference the FCC. i had a person-to-person contact at the broadcaster and figured they ought to be smart enough to understand what i was writing about.


and, by the way, SCA is an abbreviation for Subcarrier COMMUNICATIONS Authority.  k?

  -73 F (-58 C)


On Sun, Feb 14, 2021 at 10:34 AM, jdow wrote:
Most of the time the 19 kHz subcarrier is invisible unless the Big Voices and Big Noise er Music stop briefly. Then they are in your face. Of course, that depends on the station being properly setup. A Q 500 IIR filter for the pilot tone makes it easier to work with it. Was that station transmitting pure MONO?

If I had to get the attention of a local station with a screwed up signal I'd try documenting it with spectrum pictures that should show the subcarrier signals and don't. When a person talking takes a long breath of air you can get a good picture if  you are lucky. The second letter would suggest the FCC might find their signal error might be interesting when they audit the station come license renewal time. That feels sort of mean to do to them. But, it could save them their license. (All correspondence must be available at the stations for public review; and, the FCC specifically includes them in that "public.")

Of course, getting mean is not always politic. I love KUSC. They are no ads public pledge funded. So they work on shoestrings. And their RDS subsystem is somewhat dorked up and apparently difficult to use. So it's all screwed up from time to time. But, I don't want to do ANYTHING to jeopardize their license.

{^_^}

On 20210214 07:51:37, kb3cs wrote:
U.S. major market (very large city) news & information stations do this. i discovered this the first time i was experimenting with decoding RBDS myself and following along in the specification document i got my hands on where it said use the 3rd harmonic of the 19 kHz pilot tone (!!).  but .. but .. i could clearly see the 57 kHz subcarrier and no 19 kHz ..   :-P

a week later i (figuratively) banged on the office door of a different station's engineer until they too noticed the subcarrier injection level of their 67 kHz reading service for the visually impaired was way too low and the service was therefore extremely noisy (program barely audible). i was dismissed on the first attempt to call their attention to the problem ("thank you for your interest" email), and later found a historical record of their MPX spectrum clearly indicating a 67 kHz subcarrier well above the noise floor. it took a further few days until magically the subcarrier level looked the same as it had a few years earlier.

  -73 C (-99 F)
[...]


jdow
 

There are stations here in the LA area, most of them, that do not show the pilot tones for extended periods of time because they are buried in the rest of the transmitted spectrum. They would be obvious once the basic FM demodulation was done, however. I wonder how their modulation system was mucked up. It is good it got fixed. (The pilot tones give no help for SCA signals, although therer is mention that SCA signals can get pushed out to 76 kHz which is a harmonic of 19  kHz.) And it is dubious to consider some of the SCA signals "communications" when it's pure elevator mushic (sic).

{^_-}  (I have four stations in view and nary a visible 19 kHz pilot tone among them - oops, one went to talking so modulation level dropped periodically making the tone visible. There is one strong signal here that seems to be heavily compressed. Subcarriers are not visible on the RF spectrum at all except for its HDAudio "ears". The LA radio-scape is weird.)

On 20210214 17:35:48, kb3cs wrote:
the 19 kHz pilot tone is visually obvious and rarely observed less than 20 dB above the MPX spectrum floor.
none o'yer fancy filterin' needed, can just eyeball it if yer glasses didn't get too dirty.

yes, jdow, really and for true, the FM station observed sent nothing but PURE FREAKIN' MONO. mainly to extend their service region.
Mono plus the RBDS subcarrier to make all those consumer radio text readouts say useful things about which type program is being broadcast on each segment of the hour.

i learned my mistake was to contact the second Stereo+subcarrier (non-mono) broadcaster's technical personnel using only words and numbers.

the second time i included annotated IMAGES of the 'before' and 'after' MPX spectrum and short to-the-point paragraphs.   :-P

i also clued-in the sponsor of the visually impaired reading service the following week.

at no time did i reference the FCC. i had a person-to-person contact at the broadcaster and figured they ought to be smart enough to understand what i was writing about.


and, by the way, SCA is an abbreviation for Subcarrier COMMUNICATIONS Authority.  k?

  -73 F (-58 C)

On Sun, Feb 14, 2021 at 10:34 AM, jdow wrote:
Most of the time the 19 kHz subcarrier is invisible unless the Big Voices and Big Noise er Music stop briefly. Then they are in your face. Of course, that depends on the station being properly setup. A Q 500 IIR filter for the pilot tone makes it easier to work with it. Was that station transmitting pure MONO?

If I had to get the attention of a local station with a screwed up signal I'd try documenting it with spectrum pictures that should show the subcarrier signals and don't. When a person talking takes a long breath of air you can get a good picture if  you are lucky. The second letter would suggest the FCC might find their signal error might be interesting when they audit the station come license renewal time. That feels sort of mean to do to them. But, it could save them their license. (All correspondence must be available at the stations for public review; and, the FCC specifically includes them in that "public.")

Of course, getting mean is not always politic. I love KUSC. They are no ads public pledge funded. So they work on shoestrings. And their RDS subsystem is somewhat dorked up and apparently difficult to use. So it's all screwed up from time to time. But, I don't want to do ANYTHING to jeopardize their license.

{^_^}

On 20210214 07:51:37, kb3cs wrote:
U.S. major market (very large city) news & information stations do this. i discovered this the first time i was experimenting with decoding RBDS myself and following along in the specification document i got my hands on where it said use the 3rd harmonic of the 19 kHz pilot tone (!!).  but .. but .. i could clearly see the 57 kHz subcarrier and no 19 kHz ..   :-P

a week later i (figuratively) banged on the office door of a different station's engineer until they too noticed the subcarrier injection level of their 67 kHz reading service for the visually impaired was way too low and the service was therefore extremely noisy (program barely audible). i was dismissed on the first attempt to call their attention to the problem ("thank you for your interest" email), and later found a historical record of their MPX spectrum clearly indicating a 67 kHz subcarrier well above the noise floor. it took a further few days until magically the subcarrier level looked the same as it had a few years earlier.

  -73 C (-99 F)
[...]