IBOC effect on FM composite signal?

[ssnake]

What impact does IBOC have on the demodulated output of an FM station, when viewed on a spectrum analyzer? Assume a professional mod monitor is being used.

Since the IBOC system uses adjacent bandwidth instead of a subcarrier on the FM, does this show up as an increased noise floor? Does the interference ramp-up for higher baseband frequencies?

 

[NECRAT]

Here is a picture of an IBOC signal (WHCN) on a spec-anz.

> What impact does IBOC have on the demodulated output of an
> FM station, when viewed on a spectrum analyzer? Assume a
> professional mod monitor is being used.
>
> Since the IBOC system uses adjacent bandwidth instead of a
> subcarrier on the FM, does this show up as an increased
> noise floor? Does the interference ramp-up for higher
> baseband frequencies?
>

On this page http://www.necrat.com/whcn_pro.html

go about halfway down to see it.

 

[nd2023]

Re: Here is a picture of an IBOC signal (WHCN) on a spec-anz.

> > What impact does IBOC have on the demodulated output of an
>
> > FM station, when viewed on a spectrum analyzer? Assume a
> > professional mod monitor is being used.
> >
> > Since the IBOC system uses adjacent bandwidth instead of a
>
> > subcarrier on the FM, does this show up as an increased
> > noise floor? Does the interference ramp-up for higher
> > baseband frequencies?
> >
>
> On this page http://www.necrat.com/whcn_pro.html
>
> go about halfway down to see it.
>
If there is multipath, the station's IBOC hash interferes with the main analog signal. However, when an IBOC station was running a dead carrier, I turned up the volume all the way and heard dead silence (even in stereo), so the noise floor isn't increased.<P ID="signature">______________
17-year-old radio geek
Location: Princeton Junction, NJ
AIM: KewlDude471</P>

 

[ssnake]

Re: Here is a picture of an IBOC signal (WHCN) on a spec-anz.

> If there is multipath, the station's IBOC hash interferes
> with the main analog signal. However, when an IBOC station
> was running a dead carrier, I turned up the volume all the
> way and heard dead silence (even in stereo), so the noise
> floor isn't increased.

FM isn't affected that much by random noise, but it should have some effect on SNR. I imagine the analog multipath would be worsened as a result.

I know that it has been argued that the 67/92 kHz SCAs are not impacted, but has anyone taken pictures of the demodulated composite signal on a specan before and after the IBOC sidebands are transmitted? Just looking at the RF, you see the sidebands, but that doesn't demonstrate the impact on the demodulated signal.

Is IBOC interference worsened by running a greater deviation, like 110%?

 

[4dude]

> On this page http://www.necrat.com/whcn_pro.html
>
> go about halfway down to see it.
>

I see it but it doesnt make me like it anymore......... (I especially hate it from .53Mhz to 1.7Mhz)

 

[ChiefEngineer]

Making satellite radio more valuable and their old friend fm so invaluable listeners will continue to leave terrestrial listening in droves?

 

[4dude]

I hope not...........

 

[Tom Wells]

> > What impact does IBOC have on the demodulated output of an
>
> > FM station, when viewed on a spectrum analyzer? Assume a
> > professional mod monitor is being used.
> >
> > Since the IBOC system uses adjacent bandwidth instead of a
>
> > subcarrier on the FM, does this show up as an increased
> > noise floor? Does the interference ramp-up for higher
> > baseband frequencies?
> >
>
> On this page http://www.necrat.com/whcn_pro.html
>
> go about halfway down to see it.
>
If there is multipath, the station's IBOC hash interferes with the main analog signal. However, when an IBOC station was running a dead carrier, I turned up the volume all the way and heard dead silence (even in stereo), so the noise floor isn't increased.<P ID="signature">______________
17-year-old radio geek
Location: Princeton Junction, NJ
AIM: KewlDude471</P>

The noise isn't increased when there's no audio. When there is audio, being demodulated to stereo, the effect sounds exactly like weak multipath interference. It is not a pronounced effect, and unlikely to be noticed by most listeners.
It is evident when using headphones, or have the radio turned up to "full attention" levels.
I make this judgement from listening to FMs 7 miles from downtown Chicago, with strong signals.
I do have problems with some stations not demodulating to stereo since IBOC.