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IBOC and lightning
- Thread starter Link
- Start date
K
k9ez
Guest
> So what happens when listening to one of the big chicago
> IBOC stations at 670,720 or 780 and lightning occurs? Does
> the digital audio get affected?
>
You read my mind.
I was driving through Chicago last night listening. In the metro area I didnt have any troubles at all. Cant say for fringe areas however.
> IBOC stations at 670,720 or 780 and lightning occurs? Does
> the digital audio get affected?
>
You read my mind.
I was driving through Chicago last night listening. In the metro area I didnt have any troubles at all. Cant say for fringe areas however.
There is a post over on the RWOnline site (Guy Wire mailbag) from a group director of engineering (who appears to be an IBOC proponent) that says, in part, this:
"Broadband noise and static crashes kill the digital lock, and in-band, on-channel AM is really in-band, adjacent-channel. The primary digital sidebands are centered at +/- 15 kHz."
This raises real questions about the real world durability of the IBOC signal.
The basic nature of the double sideband AM signal renders it succeptable to fading as a result of received re-radiation from objects near the reciever. Power lines, building steel, etc can result in a fade on a local signal when the sidebands reach the reciever out of phase. Adding digital information over and around the DSB AM signal looks like trouble waiting to happen. When the DSB signal fades, it would be overcome by the digital noise. Building penetration and reception in noisy environments can be expected to go way down.
There is another thread on this board where the impact of IBOC on WGN is discussed. From my point of view, the real issue is not whether the on channel hiss clears the reciever filter, it is whether the IBOC digital information impairs the listenability/durability of the analog signal.
> So what happens when listening to one of the big chicago
> IBOC stations at 670,720 or 780 and lightning occurs? Does
> the digital audio get affected?
>
"Broadband noise and static crashes kill the digital lock, and in-band, on-channel AM is really in-band, adjacent-channel. The primary digital sidebands are centered at +/- 15 kHz."
This raises real questions about the real world durability of the IBOC signal.
The basic nature of the double sideband AM signal renders it succeptable to fading as a result of received re-radiation from objects near the reciever. Power lines, building steel, etc can result in a fade on a local signal when the sidebands reach the reciever out of phase. Adding digital information over and around the DSB AM signal looks like trouble waiting to happen. When the DSB signal fades, it would be overcome by the digital noise. Building penetration and reception in noisy environments can be expected to go way down.
There is another thread on this board where the impact of IBOC on WGN is discussed. From my point of view, the real issue is not whether the on channel hiss clears the reciever filter, it is whether the IBOC digital information impairs the listenability/durability of the analog signal.
> So what happens when listening to one of the big chicago
> IBOC stations at 670,720 or 780 and lightning occurs? Does
> the digital audio get affected?
>
> There is a post over on the RWOnline site (Guy Wire mailbag)
> from a group director of engineering (who appears to be an
> IBOC proponent) that says, in part, this:
>
> "Broadband noise and static crashes kill the digital lock,
> and in-band, on-channel AM is really in-band, adjacent-channel.
> The primary digital sidebands are centered at +/- 15 kHz."
The AM HD sidebands extend from slightly more than +/-10 kHz to about +/-15 kHz from the analog carrier, so they are centered at more like +/-12.5 kHz.
> This raises real questions about the real world durability
> of the IBOC signal. ... Adding digital information over
> and around the DSB AM signal looks like trouble waiting
> to happen. When the DSB signal fades, it would be overcome
> by the digital noise.
The selectivity of an analog-only receiver should prevent it from receiving the HD carriers of an HD+analog station it is tuned to, under those conditions. If an analog receiver doesn't hear the two adjacent-channel analog stations during deep fades of an analog station it is tuned to, it shouldn't hear the digital carriers of that same station, either.
> from a group director of engineering (who appears to be an
> IBOC proponent) that says, in part, this:
>
> "Broadband noise and static crashes kill the digital lock,
> and in-band, on-channel AM is really in-band, adjacent-channel.
> The primary digital sidebands are centered at +/- 15 kHz."
The AM HD sidebands extend from slightly more than +/-10 kHz to about +/-15 kHz from the analog carrier, so they are centered at more like +/-12.5 kHz.
> This raises real questions about the real world durability
> of the IBOC signal. ... Adding digital information over
> and around the DSB AM signal looks like trouble waiting
> to happen. When the DSB signal fades, it would be overcome
> by the digital noise.
The selectivity of an analog-only receiver should prevent it from receiving the HD carriers of an HD+analog station it is tuned to, under those conditions. If an analog receiver doesn't hear the two adjacent-channel analog stations during deep fades of an analog station it is tuned to, it shouldn't hear the digital carriers of that same station, either.
> > There is a post over on the RWOnline site (Guy Wire
> mailbag)
> > from a group director of engineering (who appears to be an
>
> > IBOC proponent) that says, in part, this:
> >
> > "Broadband noise and static crashes kill the digital lock,
>
> > and in-band, on-channel AM is really in-band,
> adjacent-channel.
> > The primary digital sidebands are centered at +/- 15 kHz."
>
>
> The AM HD sidebands extend from slightly more than +/-10 kHz
> to about +/-15 kHz from the analog carrier, so they are
> centered at more like +/-12.5 kHz.
>
> > This raises real questions about the real world durability
>
> > of the IBOC signal. ... Adding digital information over
> > and around the DSB AM signal looks like trouble waiting
> > to happen. When the DSB signal fades, it would be
> overcome
> > by the digital noise.
>
> The selectivity of an analog-only receiver should prevent it
> from receiving the HD carriers of an HD+analog station it is
> tuned to, under those conditions. If an analog receiver
> doesn't hear the two adjacent-channel analog stations during
> deep fades of an analog station it is tuned to, it shouldn't
> hear the digital carriers of that same station, either.
>
Good point, and I think that would be correct if the analog and digital information were in the same envelope. But they are not. When the equal amplitude DSB AM signals begin to cancel each other out, the binary stuff is still there. In essence, the hybrid signal begins to jam itself.
> mailbag)
> > from a group director of engineering (who appears to be an
>
> > IBOC proponent) that says, in part, this:
> >
> > "Broadband noise and static crashes kill the digital lock,
>
> > and in-band, on-channel AM is really in-band,
> adjacent-channel.
> > The primary digital sidebands are centered at +/- 15 kHz."
>
>
> The AM HD sidebands extend from slightly more than +/-10 kHz
> to about +/-15 kHz from the analog carrier, so they are
> centered at more like +/-12.5 kHz.
>
> > This raises real questions about the real world durability
>
> > of the IBOC signal. ... Adding digital information over
> > and around the DSB AM signal looks like trouble waiting
> > to happen. When the DSB signal fades, it would be
> overcome
> > by the digital noise.
>
> The selectivity of an analog-only receiver should prevent it
> from receiving the HD carriers of an HD+analog station it is
> tuned to, under those conditions. If an analog receiver
> doesn't hear the two adjacent-channel analog stations during
> deep fades of an analog station it is tuned to, it shouldn't
> hear the digital carriers of that same station, either.
>
Good point, and I think that would be correct if the analog and digital information were in the same envelope. But they are not. When the equal amplitude DSB AM signals begin to cancel each other out, the binary stuff is still there. In essence, the hybrid signal begins to jam itself.
> Good point, and I think that would be correct if the analog
> and digital information were in the same envelope. But they
> are not. When the equal amplitude DSB AM signals begin to
> cancel each other out, the binary stuff is still there. In
> essence, the hybrid signal begins to jam itself.
______________
But the binary stuff of a given HD+AM station occupies spans of the r-f spectrum outside the r-f passband of the typical analog AM receiver. That receiver shouldn't receive any HD carriers of the analog carrier it was tuned to, even if there was no analog modulation on it in the first place.
> and digital information were in the same envelope. But they
> are not. When the equal amplitude DSB AM signals begin to
> cancel each other out, the binary stuff is still there. In
> essence, the hybrid signal begins to jam itself.
______________
But the binary stuff of a given HD+AM station occupies spans of the r-f spectrum outside the r-f passband of the typical analog AM receiver. That receiver shouldn't receive any HD carriers of the analog carrier it was tuned to, even if there was no analog modulation on it in the first place.
R
rbrucecarter
Guest
> But the binary stuff of a given HD+AM station occupies spans
> of the r-f spectrum outside the r-f passband of the typical
> analog AM receiver.
I have to laugh whenever I read this. Most of the new cheapie AM radios use a single, poor quality ceramic filter as their entire IF. I found one radio that had a +/- 40 kHz bandwidth as a result. Which was probably a good thing, because the mechancial lash from its poorly designed dial mechanism makes it hard to tune a station. And IBOC self jams like crazy on it - the speaker is very small - would make an excellent tweeter if it wasn't the primary speaker in the radio, and the 10-15 kHz sidebands are completely annoying. Add to that the fact it is virtually impossible to tune the thing on channel, and you can hear significant hiss on the 5 to 10 kHz sidebnads, because the phase modulation becomes amplitude modulation unless you are perfectly tuned.
The "typical" AM receiver you are talking about is an obsolete reference design using three IF filter cans - and hasn't been manufactured now in several years. Most of the new IC's used for AM/FM radios use a single ceramic filter for both bands. And AM is therefore broadband - not by design for good sound - but by default because the IF is so poor.
> of the r-f spectrum outside the r-f passband of the typical
> analog AM receiver.
I have to laugh whenever I read this. Most of the new cheapie AM radios use a single, poor quality ceramic filter as their entire IF. I found one radio that had a +/- 40 kHz bandwidth as a result. Which was probably a good thing, because the mechancial lash from its poorly designed dial mechanism makes it hard to tune a station. And IBOC self jams like crazy on it - the speaker is very small - would make an excellent tweeter if it wasn't the primary speaker in the radio, and the 10-15 kHz sidebands are completely annoying. Add to that the fact it is virtually impossible to tune the thing on channel, and you can hear significant hiss on the 5 to 10 kHz sidebnads, because the phase modulation becomes amplitude modulation unless you are perfectly tuned.
The "typical" AM receiver you are talking about is an obsolete reference design using three IF filter cans - and hasn't been manufactured now in several years. Most of the new IC's used for AM/FM radios use a single ceramic filter for both bands. And AM is therefore broadband - not by design for good sound - but by default because the IF is so poor.
> > But the binary stuff of a given HD+AM station occupies
> spans
> > of the r-f spectrum outside the r-f passband of the
> typical
> > analog AM receiver.
>
> I have to laugh whenever I read this. Most of the new
> cheapie AM radios use a single, poor quality ceramic filter
> as their entire IF. I found one radio that had a +/- 40 kHz
> bandwidth as a result. Which was probably a good thing,
> because the mechancial lash from its poorly designed dial
> mechanism makes it hard to tune a station. And IBOC self
> jams like crazy on it - the speaker is very small - would
> make an excellent tweeter if it wasn't the primary speaker
> in the radio, and the 10-15 kHz sidebands are completely
> annoying. Add to that the fact it is virtually impossible
> to tune the thing on channel, and you can hear significant
> hiss on the 5 to 10 kHz sidebnads, because the phase
> modulation becomes amplitude modulation unless you are
> perfectly tuned.
>
> The "typical" AM receiver you are talking about is an
> obsolete reference design using three IF filter cans - and
> hasn't been manufactured now in several years. Most of the
> new IC's used for AM/FM radios use a single ceramic filter
> for both bands. And AM is therefore broadband - not by
> design for good sound - but by default because the IF is so
> poor.
>
Absolutely right.
Plus the assertion that the binary info is outside the passband of the reciever is not entirely correct. Don't forget the QPSK tertiary signals that are under the analog signals. When the DSB AM fades due to re-radiated signals reaching the receiver out of phase, the non-AM digital is all that's left.
Now listenable analog signals in areas prone local fades (such as inside buildings with metal substructure) will become apparently more noisy because of the introduction of the digital information.
> spans
> > of the r-f spectrum outside the r-f passband of the
> typical
> > analog AM receiver.
>
> I have to laugh whenever I read this. Most of the new
> cheapie AM radios use a single, poor quality ceramic filter
> as their entire IF. I found one radio that had a +/- 40 kHz
> bandwidth as a result. Which was probably a good thing,
> because the mechancial lash from its poorly designed dial
> mechanism makes it hard to tune a station. And IBOC self
> jams like crazy on it - the speaker is very small - would
> make an excellent tweeter if it wasn't the primary speaker
> in the radio, and the 10-15 kHz sidebands are completely
> annoying. Add to that the fact it is virtually impossible
> to tune the thing on channel, and you can hear significant
> hiss on the 5 to 10 kHz sidebnads, because the phase
> modulation becomes amplitude modulation unless you are
> perfectly tuned.
>
> The "typical" AM receiver you are talking about is an
> obsolete reference design using three IF filter cans - and
> hasn't been manufactured now in several years. Most of the
> new IC's used for AM/FM radios use a single ceramic filter
> for both bands. And AM is therefore broadband - not by
> design for good sound - but by default because the IF is so
> poor.
>
Absolutely right.
Plus the assertion that the binary info is outside the passband of the reciever is not entirely correct. Don't forget the QPSK tertiary signals that are under the analog signals. When the DSB AM fades due to re-radiated signals reaching the receiver out of phase, the non-AM digital is all that's left.
Now listenable analog signals in areas prone local fades (such as inside buildings with metal substructure) will become apparently more noisy because of the introduction of the digital information.
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