IBOC

IBOC

Post by Maximu » Mon, 23 Feb 2004 23:15:07

I saw a reference to this and wondered what it was. Below is a link I found
using Google:

http://www.ibiquity.com/technology/index.htm

 I can't see how it will do anything but cause serious problems for
shortwave, let alone AM. I don't fancy having to replace any radios I have.
Since people already have cell phones capable of sending and receiving
email, pictures and news, it would seem redundant. What would make people
want this over their existing cell phones ?

Il Dolce Far Niente

 
 
 

IBOC

Post by Frank Dresse » Tue, 24 Feb 2004 01:03:58



Quote:> I saw a reference to this and wondered what it was. Below is a link I
found
> using Google:

> http://www.ibiquity.com/technology/index.htm

>  I can't see how it will do anything but cause serious problems for
> shortwave, let alone AM.

There hasn't been any push to use IBOC on shortwave.  It's been designed
for domestic AM and FM broadcasters.  There's a different non-compatible
digital standard for shortwave called DRM.

Quote:> I don't fancy having to replace any radios I have.

IBOC is sorta compatible with standard AM broadcasting.  The standard AM
channel is still there, with additional channels of digital modulation
just above and below the standard channel.  Unfortunately, the fidelity
of the standard channel must be reduced, and the digital channels can
cause severe interference with adjacent channels.  IBOC isn't compatible
with DXing stations close in frequency to an IBOC station, and buying
another radio won't help.

Quote:> Since people already have cell phones capable of sending and receiving
> email, pictures and news, it would seem redundant. What would make
people
> want this over their existing cell phones ?

Even the "journalists" who do little more than reword corporate press
handouts aren't showing much enthusisiam for IBOC broadcasting to cell
phones.  Anyway, I'd expect the IBOC cell phone broadcasters will be
trying FM band transmitters rather than AM band transmitters.

There are claims that there is a great unfilled demand for slow text and
low-res graphics and pictures on our radios and, by golly, the IBOC folk
will step up to the plate and fufill that demand.  Imagine that!
Pictures on the radio.  What will they think of next?

Frank Dresser

 
 
 

IBOC

Post by Steve Ston » Tue, 24 Feb 2004 05:13:39

Quote:

> >  I can't see how it will do anything but cause serious problems for
> > shortwave, let alone AM.

You won't hear much of anything under 400 mhz once broadband over power lines ramps up to full
bore.

Do a gOOgle search on BPL,

Steve

 
 
 

IBOC

Post by Frank Dresse » Tue, 24 Feb 2004 05:27:00


Quote:

> You won't hear much of anything under 400 mhz once broadband over

power lines ramps up to full

Quote:> bore.

> Do a gOOgle search on BPL,

> Steve

I'm lazy.  How 'bout you gOOgle up some links concerning this "You won't
hear much of anything under 400 mhz " business?

Oh, yeah.  Don't forget to share your knowledge with the TV and radio
networks.  For some reason, they don't seem concerned.

Frank Dresser

 
 
 

IBOC

Post by Brenda An » Tue, 24 Feb 2004 05:46:17




> > You won't hear much of anything under 400 mhz once broadband over
> power lines ramps up to full
> > bore.

> > Do a gOOgle search on BPL,

> > Steve

> I'm lazy.  How 'bout you gOOgle up some links concerning this "You won't
> hear much of anything under 400 mhz " business?

> Oh, yeah.  Don't forget to share your knowledge with the TV and radio
> networks.  For some reason, they don't seem concerned.

400 MHz is a bit of an exaggeration. BPL will cause considerable
interference up to it's limit of 75MHz, and may cause some harmonic
interference above that (it IS square wave after all, and high in harmonic
content).

It won't (or shouldn't) affect the AMBCB, since it is supposed to start at
1.8 MHz. However, there have been several tests performed by hams and some
labs (see the ARRL website www.arrl.org), and several countries have already
banned BPL because of extreme interference to other services, including HF
broadcast and amateur radio services. I don't remember the exact numbers,
but basically if you are within 30 feet of a BPL line, you will receive in
excess of S9 (some tests have shown 30 dB over S9) of interference.

 
 
 

IBOC

Post by Frank Dresse » Tue, 24 Feb 2004 06:06:59


Quote:

> 400 MHz is a bit of an exaggeration. BPL will cause considerable
> interference up to it's limit of 75MHz, and may cause some harmonic
> interference above that (it IS square wave after all, and high in
harmonic
> content).

Oh, I know.  I've done my fair share of usenet posts on the BPL topic.
The original poster makes a very good point, though.  It is easy to
research.

Quote:

> It won't (or shouldn't) affect the AMBCB, since it is supposed to
start at
> 1.8 MHz. However, there have been several tests performed by hams and
some
> labs (see the ARRL website www.arrl.org), and several countries have
already
> banned BPL because of extreme interference to other services,
including HF
> broadcast and amateur radio services. I don't remember the exact
numbers,
> but basically if you are within 30 feet of a BPL line, you will
receive in
> excess of S9 (some tests have shown 30 dB over S9) of interference.

I really doubt BPL will have any noticable effects on AM/FM/TV
reception.  After all, the networks haven't used any of their
considerable clout in Washington in the BPL fight.  I suspect consumer
electronics will be most subject to any BPL effects throught the power
cord and not the antenna terminals.  If this has been a problem in the
test areas, I'm not aware of it.

But I wonder if BPL will work as promised and if it will be a good deal
for the consumers.  Power lines are an awfully primitave way to deliver
high speed access, and I can imgaine alot of problems.  If BPL doesn't
work out, the utilities might have to fall back on BWP (Broadband over
Water Pipes).

Frank Dresser

 
 
 

IBOC

Post by Telamo » Tue, 24 Feb 2004 06:16:08







> > > You won't hear much of anything under 400 mhz once broadband over
> > power lines ramps up to full
> > > bore.

> > > Do a gOOgle search on BPL,

> > > Steve

> > I'm lazy.  How 'bout you gOOgle up some links concerning this "You won't
> > hear much of anything under 400 mhz " business?

> > Oh, yeah.  Don't forget to share your knowledge with the TV and radio
> > networks.  For some reason, they don't seem concerned.

> 400 MHz is a bit of an exaggeration. BPL will cause considerable
> interference up to it's limit of 75MHz, and may cause some harmonic
> interference above that (it IS square wave after all, and high in harmonic
> content).

> It won't (or shouldn't) affect the AMBCB, since it is supposed to start at
> 1.8 MHz. However, there have been several tests performed by hams and some
> labs (see the ARRL website www.arrl.org), and several countries have already
> banned BPL because of extreme interference to other services, including HF
> broadcast and amateur radio services. I don't remember the exact numbers,
> but basically if you are within 30 feet of a BPL line, you will receive in
> excess of S9 (some tests have shown 30 dB over S9) of interference.

Data communications occupy wider bandwidths than the stated clock rate.
It is not unreasonable to expect harmonics 3 to 5 times the clock rate
because the signaling uses square waves and there is significant power
in the odd harmonics.

--
Telamon
Ventura, California

 
 
 

IBOC

Post by Frank Dresse » Tue, 24 Feb 2004 09:07:12


Quote:

> Data communications occupy wider bandwidths than the stated clock
rate.
> It is not unreasonable to expect harmonics 3 to 5 times the clock rate
> because the signaling uses square waves and there is significant power
> in the odd harmonics.

> --
> Telamon
> Ventura, California

A square wave, itself, won't convey much information.  It needs to be
modulated, and the modulation would have to effect the symmetry and
result in both odd and even harmonics.

I don't know what sort of modulation BPL is using.  I can imagine
hundreds of low amplitude sine wave carriers from 2 to 60 Mhz, all of
them phase modulated.  In that case, I don't think there would be much
harmonic output.  This would certainly still be a big problem for the
radio hobbyist, but not so much for the FM/TV user.  There have been
several BPL tests in various communities, and it doesn't seem to have
wiped out normal broadcast use.

If BPL caused enough bothersome interference to keep people in the test
communities from their TVs and radios, the National Association of
Broadcasters would have squashed it like a bug.

Frank Dresser

 
 
 

IBOC

Post by Brenda An » Tue, 24 Feb 2004 09:14:56




> > Data communications occupy wider bandwidths than the stated clock
> rate.
> > It is not unreasonable to expect harmonics 3 to 5 times the clock rate
> > because the signaling uses square waves and there is significant power
> > in the odd harmonics.

> > --
> > Telamon
> > Ventura, California

> A square wave, itself, won't convey much information.  It needs to be
> modulated, and the modulation would have to effect the symmetry and
> result in both odd and even harmonics.

> I don't know what sort of modulation BPL is using.  I can imagine
> hundreds of low amplitude sine wave carriers from 2 to 60 Mhz, all of
> them phase modulated.  In that case, I don't think there would be much
> harmonic output.

Digital comms are purely square waves.  The modulation is FSK or similar
(generally)... in other words, the on-state is one frequency, the off state
is another.  This creates a chain of square waves which themselves are not
modulated. The bandwidth, in this case 75 MHz, is how many on/off states
there are in one second. This is also concurrent with bitrate. Compression
schemes can raise the apparent bitrate, however the actual bitrate is the
same as the frequency used.  I'm not sure how they do the band notching that
Japan tried before they tossed out the idea completely.
 
 
 

IBOC

Post by Frank Dresse » Tue, 24 Feb 2004 09:50:53


Quote:

> Digital comms are purely square waves.

I'm using the term "square wave" to mean a sharp cornered pulse train
with an exactly 50% duty cycle.  There's not much information there.
You've seen one pulse of the square wave, you've seen them all.

Quote:>The modulation is FSK or similar
> (generally)... in other words, the on-state is one frequency, the off
state
> is another.  This creates a chain of square waves which themselves are
not
> modulated.

And the square wave is recovered after only after demodulation of the
sine waves.  The modulation doesn't necessaraly create harmonics, but it
does create sidebands.

This guy likes to use triangle waves in his illustrations:

http://www.cs.ucl.ac.uk/staff/S.Bhatti/D51-notes/node12.html

Quote:>The bandwidth, in this case 75 MHz, is how many on/off states
> there are in one second. This is also concurrent with bitrate.
Compression
> schemes can raise the apparent bitrate, however the actual bitrate is
the
> same as the frequency used.

The carriers can be both amplitude and phase modulated to increase
bitrate.

Given that the BPL is usually described as a spread spectrum technology,
I'll assume there's many carrier frequencies.

Quote:> I'm not sure how they do the band notching that
> Japan tried before they tossed out the idea completely.

Doesn't Japan have a higher percentage of SWLs and radio amateurs than
the US?  I don't think most Americans will much care about BPL unless it
effects the TV.  I'll bet the BPL traps at 3.58 MHz work just fine.

Frank Dresser

 
 
 

IBOC

Post by Steve Ston » Tue, 24 Feb 2004 11:11:34

From:
http://www.qrpis.org/~k3ng/bpl.html
-----------

Q: What is intermodulation?

A: Intermodulation is the mixing of radio signals which produces new radio signals. Think of
it as radio waves having children. But just how do radio waves have children ?

This mixing is caused by what are called non-linearities. One non-linear electronic component
that you find in most any electronic device is a diode. When multiple radio signals are run
through the diode, they mix together. Let's say we have a 4 Mhz signal and a 6 Mhz signal
going into the diode. We would then get:

4 + 6 = 10 Mhz

6 ? 4 = 2 Mhz

4 and 6 Mhz had two ?children?, 2 and 10 Mhz !

Now, non-linearities are usually good. This phenomenon is used in just about every radio
device to either create a signal to be transmitted, or receive a signal that you hear or see.
But, non-linearities can occur where you don't want them and then in causes problems. One such
place is in power lines. Bad, corroded connections or dissimilar metals touching can create
natural diodes that act like mixers and produce this intermodulation.

So, let's take a BPL signal and for the sake of discussion, say it's a grossly simplified
consisting of radio signals at 1, 5, 8, 9, and 12 Mhz. Some of the intermodulation products
that could be created would be:

1 + 5 = 6 Mhz

8 + 9 = 17 Mhz

9 + 12 = 21 Mhz

12 ? 9 = 3 Mhz

But you could also have what is known as third order products:

1 + 9 + 12 = 22 Mhz

8 + 9 + 12 = 29 Mhz

8 ? 5 + 12 = 15 Mhz

Or even:

2 * 12 = 24 Mhz

(9 ? 5) * 12 = 48 Mhz

You can do the math and figure out each permutation, but you get the idea. If we took a real
BPL signal that has signals from 1 ? 80 Mhz the number of products and where they would fall
are mind-boggling. The resulting intermodulation products in a system could extend well above
the band BPL proponents want, falling into FM broadcast, VHF TV, Aeronautical, and more public
safety bands. This is just another reason why BPL is so problematic.

It's arguable that such non-linearities in power lines are exhibited as arcing connections,
something that most power companies are actively searching for these days as the RFI (radio
frequency interference) effects are well understood. These maintenance issues will be
addressed quickly by well run utilities. However, non-linear loads are common in homes, light
dimmers being the first devices that come to mind. Theoretically, these devices could create
intermodulation that would in turn be radiated by the house wiring and outside power cabling.

 
 
 

IBOC

Post by Frank Dresse » Tue, 24 Feb 2004 12:55:02


Quote:

> From:
> http://www.qrpis.org/~k3ng/bpl.html
> -----------

> Q: What is intermodulation?

> A: Intermodulation is the mixing of radio signals which produces new

radio signals. Think of

Quote:> it as radio waves having children. But just how do radio waves have
children ?

[snip]

Reality trumps theory.  BPL is being tested.  If BPL was making much in
the way of harmonics or IMD products, the low end of the BPL spectrum
will be interfering with the high end of the BPL spectrum.  The high end
of the BPL spectrum would be interfering with TV and FM radio.

BPL's fundamentals are the confirmed problem for the radio hobbyist.  Ed
Hare and other radio amateurs have done alot of work documenting the
interference levels on SW radio.

Frank Dresser

 
 
 

IBOC

Post by Larry Ozaro » Tue, 24 Feb 2004 14:28:46

It's hard to generalize about all digital communication. I think
BPL is some kind of phase modulated OFDM as Frank says, so in that
case you could use essentially rectangular pulses (in practice there
is probably some roll-off and guard time to boot). Each individual
tone would actually occupy a bandwidth much greater than its keying
rate, but since each tone's keying rate is so low compared to the
total bandwidth, the net effect is minor, again exactly as Frank
says.

For single carrier high date rate systems however, the last thing you
want to use is rectangular pulses. The spectrum won't have discrete
harmonics but it will look like (sin(x)/x)^2 in frequency with
significant energy beyond the Nyquist frequency. In those applications a
waveform that falls off in time as t^2 is generally used, though there
are other options, like minimum-shift keying, which can be looked at
either as continuous phase FSK or QPSK using smooth shaped pulses.
Continuous phase modulation has some complications though.

Oz




>>A square wave, itself, won't convey much information.  It needs to be
>>modulated, and the modulation would have to effect the symmetry and
>>result in both odd and even harmonics.

>>I don't know what sort of modulation BPL is using.  I can imagine
>>hundreds of low amplitude sine wave carriers from 2 to 60 Mhz, all of
>>them phase modulated.  In that case, I don't think there would be much
>>harmonic output.

> Digital comms are purely square waves.  The modulation is FSK or similar
> (generally)... in other words, the on-state is one frequency, the off state
> is another.  This creates a chain of square waves which themselves are not
> modulated. The bandwidth, in this case 75 MHz, is how many on/off states
> there are in one second. This is also concurrent with bitrate. Compression
> schemes can raise the apparent bitrate, however the actual bitrate is the
> same as the frequency used.  I'm not sure how they do the band notching that
> Japan tried before they tossed out the idea completely.

 
 
 

IBOC

Post by Telamo » Tue, 24 Feb 2004 14:36:07





> > Data communications occupy wider bandwidths than the stated clock
> rate.
> > It is not unreasonable to expect harmonics 3 to 5 times the clock rate
> > because the signaling uses square waves and there is significant power
> > in the odd harmonics.

> > --
> > Telamon
> > Ventura, California

> A square wave, itself, won't convey much information.  It needs to be
> modulated, and the modulation would have to effect the symmetry and
> result in both odd and even harmonics.

> I don't know what sort of modulation BPL is using.  I can imagine
> hundreds of low amplitude sine wave carriers from 2 to 60 Mhz, all of
> them phase modulated.  In that case, I don't think there would be much
> harmonic output.  This would certainly still be a big problem for the
> radio hobbyist, but not so much for the FM/TV user.  There have been
> several BPL tests in various communities, and it doesn't seem to have
> wiped out normal broadcast use.

> If BPL caused enough bothersome interference to keep people in the test
> communities from their TVs and radios, the National Association of
> Broadcasters would have squashed it like a bug.

It is a common error to assume that digital communications are similar
to analog RF. One reason is very fast edge times are required to create
the most eye margin possible at the decoding end of a data stream so the
bandwidth required is much greater. A good rule of thumb is 3.7 times
the clock rate as a minimum. Usually the engineering shoots for the
fastest edge times practical.

An one/zero pattern and multiples thereof are square waves but I should
not have used that term because it looks like I just threw you off the
path of understanding.

--
Telamon
Ventura, California

 
 
 

IBOC

Post by Telamo » Tue, 24 Feb 2004 15:11:47



Quote:> It's hard to generalize about all digital communication. I think
> BPL is some kind of phase modulated OFDM as Frank says, so in that
> case you could use essentially rectangular pulses (in practice there
> is probably some roll-off and guard time to boot). Each individual
> tone would actually occupy a bandwidth much greater than its keying
> rate, but since each tone's keying rate is so low compared to the
> total bandwidth, the net effect is minor, again exactly as Frank
> says.

> For single carrier high date rate systems however, the last thing you
> want to use is rectangular pulses. The spectrum won't have discrete
> harmonics but it will look like (sin(x)/x)^2 in frequency with
> significant energy beyond the Nyquist frequency. In those applications a
> waveform that falls off in time as t^2 is generally used, though there
> are other options, like minimum-shift keying, which can be looked at
> either as continuous phase FSK or QPSK using smooth shaped pulses.
> Continuous phase modulation has some complications though.

I haven't read how BPL is supposed to work but is it reasonable to
expect that a encoding scheme would be used that would shift the
spectrum requirements downward so that increased coupling would be
needed across the transformers in the power system?

--
Telamon
Ventura, California