New Portable Radio for Digital Satellite

In article . com,
says...
Just to pick up on a few things (above) ......

DAB has local stations, depending on where you are, admittedly usually
just independent ones, not BBC local.


this is the problem, depending on where you live, and I bet the local
stations that are on DAb are from big cities, like London, Birmingham
and places like that.

I doubt if small cities and towns local stations will ever be on DAB.

XM and Worldspace exist, but are mainly or wholly subscription, and
more like terrestrial networks in coverage (you can't "point at" a
particular satellite). I mentioned shortwave DRM because it's also
quite similar in concept.

I think the Sky description of "digital radio" is extremely misleading,
seeing as it's only a wireless loudspeaker link to an existing digibox,
and the wording is deliberately phrased so as to disguise this (eg,
"compatible with"!).

I also find fm pirate radio highly annoying, eg when trying to listen
to R4 on Walkman, particularly since they often come up right next to
it, with much too big power/deviation, sometimes making the legit
stations unreceivable.
It's quite remarkable that you can be sent to prison for not having a
tv license, yet these pirate stations seem immune to any official
sanctions!



If they was caught, they could be sent to prison, I am amazed that
nothing is done about them. We do not have the problem here.

In article , Harvey Van Sickle
writes
On 07 Aug 2005, Prometheus wrote

-snip quotes from relevant acts, and interpretation of same-

Your e-mail from the TVL folk about Freeview receivers states one
fact (that a licence is required for a TV receiver as stated in
CA2003) and then makes an unsubstantiated assertion (not stated in
any Act) in the hope you will think it is also a fact and hand
them some money.

Do you think that my reading the published legislation is "vacuous
and ill-informed theorising"?

Until the implementation of the act is tested in court, it's simply
your reading and interpretation of the relevant legislation against
TVL's reading and interpretation of exactly the same legislation.

As you rightly point out, TVL's assertion is "unsubstantiated": so is
your statement -- -which is based on your reading of the act rather
than on case law. Until case law exists, it's all theorising, vacuous
or otherwise.

TVL would have to cite an SI or Act defining an STB as a Colour
Television Receiver, I do not have to show that no SI or Act does not.
--
Ian G8ILZ

Unfortunately, "DAB" is wrong in most of what he says, as I shall
now show .....

(whether through ignorance, or deliberately, I don't know, but
suspect the latter).

(Please forgive me for repeating some stuff, but "DAB" has utterly
confused things!).

1) The Gnome is a digibox extension wireless loudspeaker, "usable"
as a digital radio (if not too far away from digibox!), and a nice
gadget, in fact I might get one!

2) In the UK, broadcast radio receivers are unrestricted, but
broadcast tv receivers require a tv license.

3) The Gnome requires a tv license (try using it without one, then wait
and see what happens!).

4) A Ku band "portable satellite radio receiver" is a nice idea,
but would be practically impossible, due to the dish aerial.

5) But, as Angus Rae quite rightly points out, there are some 3Ghz
dedicated sat radio broadcast systems, with genuinely portable
receivers.

6) However, due to the poor receiving antenna, such receivers have much
worse SNR, hence a limited bandwidth (approx 150 radio "channels"
total, compared with 1000s of tv and radio channels receivable on Ku
band, at least in Europe ).

6) Digital broadcast reception is critically dependent on SNR, hence
the antenna (as people trying to get it often find out!).

7) With XM (for example), due to the poor antenna, signal strength must
be hugely increased, as "DAB" rightly points out (which directly
improves the SNR!).

8) More bandwidth could be used, in theory, but real satellites have
power limitations, thus limiting the transmitted bandwidth (ie,
constant gain-bandwidth product, for a fixed power). That's why I
said, quite clearly, NOT from Shannon's formula!

9) DAB's use of the Shannon formula is wrong, because S/R is
bandwidth dependent (since, in a Gaussian Channel, noise power is
directly proportional to bandwidth).

For example, 4Khz bandwidth and S/R of 7 gives same C value as 3Khz
bandwidth and S/R of 15, but noise power also decreases by a quarter,
which means a 25% bandwidth reduction needs a 60% S/R increase for same
C value.

(Sorry DAB, full marks for arithmetic, but zero for science!).

(I personally am an "analogue man", so still intuitively think
"channel capacity is proportional to bandwidth" and find this above
result hard to believe, but it's true!).

(Shannon's formula is just an "upper bound", not much use in
calculation with actual systems, where you really need the error
probability).

10) "Spectral efficiency" has several possible meanings (even with
the units "DAB" gave!). One possible meaning is just re-arranging
the Shannon formula, another is the current "trendy" one of
"useful bits per buck", which includes the modulation and error
coding systems used, but gives no idea of "system robustness",
maybe useful if you're an accountant "buying" radio spectrum for
mobile phone companies.

As I say, spectral efficiency is a useful concept, but certainly not a
complete system description. For example, Ku band satellite uses DPSK
modulation, and "fits" an MPEG2 mux into 27Mhz bandwidth, whereas
Freeview/top-up uses only 8Mhz!. But, there's currently only about 50
UK DTT "channels" receivable, and thousands of Ku band ones!

11) As to "Dab is worse than FM", I don't have a DAB receiver,
but completely take "DAB"'s word for it. Presumably, the BBC
allocate much bandwith to Radio 3, and other channels will then sound
bad. The BBC would probably say something like "we're not in the Hi
Fi business" (they've said that to me!), and UK commercial radio
don't care, just so long as the money rolls in! Since UK DAB is sold
as "improved audio quality, crystal clear reception!", yes I agree
that's untrue.

12) I'm not "always right", in fact I've previously made an ass
of myself by not properly reading questions and statements in posts,
and also by using poorly defined terms. However, I do resent this sort
of gross misrepresentation of what I've said. Not so much from my
poor wounded ego, but because it confuses other people.

That's all!

spiney wrote:
Unfortunately, "DAB" is wrong in most of what he says, as I shall
now show .....


Seeing as you've been talking nonsense up to now I doubt what you will
show will prove a thing.


(whether through ignorance, or deliberately, I don't know, but
suspect the latter).

(Please forgive me for repeating some stuff, but "DAB" has utterly
confused things!).

1) The Gnome is a digibox extension wireless loudspeaker, "usable"
as a digital radio (if not too far away from digibox!), and a nice
gadget, in fact I might get one!


I haven't said otherwise.


2) In the UK, broadcast radio receivers are unrestricted, but
broadcast tv receivers require a tv license.


I haven't said otherwise.


3) The Gnome requires a tv license (try using it without one, then
wait and see what happens!).


It's aimed at Sky subscribers, so they already need a TV licence.


4) A Ku band "portable satellite radio receiver" is a nice idea,
but would be practically impossible, due to the dish aerial.


I haven't said otherwise.


5) But, as Angus Rae quite rightly points out, there are some 3Ghz
dedicated sat radio broadcast systems, with genuinely portable
receivers.


I haven't said otherwise.


6) However, due to the poor receiving antenna, such receivers have
much worse SNR, hence a limited bandwidth (approx 150 radio "channels"
total, compared with 1000s of tv and radio channels receivable on Ku
band, at least in Europe ).


Here you go again. You completely ignore the fact that the signals that
are meant to be picked up with small antennas, such as XM radio signals,
have a FAR higher field strength that for Ku band signals, thus
compensating for the far lower antenna gain.


6) Digital broadcast reception is critically dependent on SNR, hence
the antenna (as people trying to get it often find out!).


See above. The overall SNR at the input of the receiver (after the
antenna) will be very similar for both systems.


7) With XM (for example), due to the poor antenna, signal strength
must be hugely increased, as "DAB" rightly points out (which directly
improves the SNR!).

8) More bandwidth could be used, in theory, but real satellites have
power limitations, thus limiting the transmitted bandwidth (ie,
constant gain-bandwidth product, for a fixed power). That's why I
said, quite clearly, NOT from Shannon's formula!


Take Astra 2D:

http://www.lyngsat.com/astra2d.html

The transponder frequencies go from 10714 MHz to 10936 MHz, with
transponders' channels separated by 15 MHz, and there's 16 transponders.
Transponder capacity is 33 Mbps, so the overall data capacity is 528
Mbps.

Compare that with XM with a data capacity of 4 Mbps in just 5 MHz of
bandwidth.

Which do you think is the most significant difference between these
systems that causes the huge difference in daata capacity?

It's the bandwidth, stupid.


9) DAB's use of the Shannon formula is wrong, because S/R is
bandwidth dependent (since, in a Gaussian Channel, noise power is
directly proportional to bandwidth).


S/R? I take it you mean SNR or S/N?

Signal power is the integration of the PSD over the signal spectrum.
Noise power is the integration of the noise PSD over the signal
spectrum.

Signal power / noise power = SNR


For example, 4Khz bandwidth and S/R of 7 gives same C value as 3Khz
bandwidth and S/R of 15, but noise power also decreases by a quarter,
which means a 25% bandwidth reduction needs a 60% S/R increase for
same C value.


What you've unwittingly done is to support the point I was making that C
is weakly dependent on SNR whereas C is directly proportional to
bandwidth.

Putting those numbers into Shannon's capacity theorem:

(i)

C = B log2 (1 + SNR)

C = 4000 log2 (1 + 7) = 12000 bps

(ii)

12000 = 3000 log2 (1 + SNR)

4 = log2 (1 + SNR)

2^4 = 1 + SNR

SNR = 15

So you've not even calculated the SNR value correctly.


(Sorry DAB, full marks for arithmetic, but zero for science!).


Sorry, you're going to have to start back at Mathematics 101, and
progress from there.


(I personally am an "analogue man", so still intuitively think
"channel capacity is proportional to bandwidth" and find this above
result hard to believe, but it's true!).


I suggest you go through your calculations.


(Shannon's formula is just an "upper bound", not much use in
calculation with actual systems, where you really need the error
probability).


Shannon's capacity theorem states the maximum bit rate at which you can
transmit, so it is an upper bound, but I would dispute the fact that it
is useless because it allows comparisons of real digital communications
systems with the theoretical optimum.


10) "Spectral efficiency" has several possible meanings (even with
the units "DAB" gave!).


Spectral efficiency is typically calculated as follows:

bit rate / bandwidth = bits/s/Hz

The other way is to use the code rate instead of the bit rate.


One possible meaning is just re-arranging
the Shannon formula, another is the current "trendy" one of
"useful bits per buck",


Both have the same units of bits/s/Hz and both are calculated by
dividing bit rate by bandwidth, so there's no difference between them.


which includes the modulation and error
coding systems used, but gives no idea of "system robustness",


System robustness is found from the BER (bit error rate) at the design
SNR.


maybe useful if you're an accountant "buying" radio spectrum for
mobile phone companies.


It's one of the main parameters considered when designing a new digital
communications system, because different modulation and coding schemes
can be compared.


As I say, spectral efficiency is a useful concept, but certainly not a
complete system description. For example, Ku band satellite uses DPSK


Nope, it uses QPSK. I presume you're getting mixed up with DQPSK, which
is differential phase shift keying. DVB-S uses synchronous modulation,
not differential modulation.


modulation, and "fits" an MPEG2 mux into 27Mhz bandwidth, whereas
Freeview/top-up uses only 8Mhz!.


That Lyngsat page showed that channel separation is 15 MHz and the
transponder data capacity is 33 Mbps.

In comparison, the BBC 16-QAM muxes are 8 MHz wide and have a capacity
of 18 Mbps. So both are about 2 bits/s/Hz.


But, there's currently only about 50
UK DTT "channels" receivable, and thousands of Ku band ones!


Absolutely.


11) As to "Dab is worse than FM", I don't have a DAB receiver,
but completely take "DAB"'s word for it. Presumably, the BBC
allocate much bandwith to Radio 3, and other channels will then sound
bad. The BBC would probably say something like "we're not in the Hi
Fi business" (they've said that to me!), and UK commercial radio
don't care, just so long as the money rolls in! Since UK DAB is sold
as "improved audio quality, crystal clear reception!", yes I agree
that's untrue.


That's very big of you.


12) I'm not "always right", in fact I've previously made an ass
of myself by not properly reading questions and statements in posts,
and also by using poorly defined terms. However, I do resent this sort
of gross misrepresentation of what I've said. Not so much from my
poor wounded ego, but because it confuses other people.


You really need to try and understand what I'm saying. You say you're an
"analogue man", well, I'm a "digital man", and I'm afraid I'm right
here.


--
Steve - www.digitalradiotech.co.uk - Digital Radio News & Info

Find the cheapest Freeview, DAB & MP3 Player Prices:
http://www.digitalradiotech.co.uk/fr..._receivers.htm
http://www.digitalradiotech.co.uk/da...tal_radios.htm
http://www.digitalradiotech.co.uk/mp...rs_1GB-5GB.htm
http://www.digitalradiotech.co.uk/mp...e_capacity.htm

Nope, what I said was quite correct! My example was taken directly from
a textbook (perhaps the textbook is wrong?!). I chose it because the
numbers are "convenient", to make working out simpler (just pencil and
paper, avoids needing a calculator!). And I checked it!

Gaussian noise power is directly proportional to bandwidth (that's
exacly what it means!). If you change the value of B, you must also
correspondingly change the value of N, otherwise, it's just gibberish!

As I say, your arithmetic is perfect, but your understanding in absent!

The rest of what I said is also correct.

Angus Rae (Edinburgh University!) claims to be an expert, perhaps, he'd
like to confirm (or deny) what I say?

Information Theory is strongly related to statistical mechanics, think
of it as "conservation of energy". For a fixed C, if B goes down, then
S/R goes up.

Good "strategic withdrawal", but still completely wrong. Sorry.

etillet wrote:
Kristoff Bonne wrote:
Gegroet,

spiney schreef:

I've looked at the above links, but sorry, you can't have a portable
digital satellite radio receiver (because it would require its own
satellite dish!).
If it's some sort of portable rf link back to a digibox ("battery
powered videosender"), then ok, that would work, but not enough info is
given to make this clear.


Does it offer some kind of "return-channel" so that you can "control"
the receiver from the kitchen/garden/...?

E.g. can you switch to another radio-station or start or shut down the
receiver at a distance?

Assuming it has a line-out socket it will be quite useful to get stereo
sound on a remote TV connected to the sky box via RF....

Nope, sorry, you need SCART for that!

spiney wrote:
Nope, what I said was quite correct! My example was taken directly
from a textbook (perhaps the textbook is wrong?!). I chose it because
the numbers are "convenient", to make working out simpler (just
pencil and paper, avoids needing a calculator!). And I checked it!

Gaussian noise power is directly proportional to bandwidth (that's
exacly what it means!). If you change the value of B, you must also
correspondingly change the value of N, otherwise, it's just gibberish!


This is what you originally said:

"A smaller antenna is inherently worse, as SNR is lower, therefore
channel capacity is reduced, regardeless of other factors (see
Shannon's formula)."

What I keep telling you is that XM Radio has a higher field strength to
compensate for the smaller antenna, and the huge difference in data
capacity between XM Radio and digital satellite transmissions received
on dish antennas is due to the huge, huge, huge difference in bandwidth
consumed.


As I say, your arithmetic is perfect, but your understanding in
absent!


My understanding is not absent at all; you seem to confuse things
completely.


The rest of what I said is also correct.

Angus Rae (Edinburgh University!) claims to be an expert, perhaps,
he'd like to confirm (or deny) what I say?

Information Theory is strongly related to statistical mechanics, think
of it as "conservation of energy". For a fixed C, if B goes down, then
S/R goes up.


That is too obvious to even comment on, because you've got an equation
of the form:

C = B x D

where D = log2 (1 + SNR), so for a fixed C, if B goes up D goes down,
and vice versa.


Good "strategic withdrawal", but still completely wrong. Sorry.


I'm not withdrawing from this at all.


--
Steve - www.digitalradiotech.co.uk - Digital Radio News & Info

Find the cheapest Freeview, DAB & MP3 Player Prices:
http://www.digitalradiotech.co.uk/fr..._receivers.htm
http://www.digitalradiotech.co.uk/da...tal_radios.htm
http://www.digitalradiotech.co.uk/mp...rs_1GB-5GB.htm
http://www.digitalradiotech.co.uk/mp...e_capacity.htm

DAB sounds worse than FM wrote:
spiney wrote:
Unfortunately, "DAB" is wrong in most of what he says, as I shall
now show .....


Seeing as you've been talking nonsense up to now I doubt what you will
show will prove a thing.

I see that spiney is still posting, I'd hoped he'd gone as I hadn't seen
any replies to him for acouple of days.
--
Adrian A

you're still doing it!

Is my assertion that your use of the Shannon formula is wrong correct,
or is it incorrect?

I don't dispute the arithmetic, it's the science that's wrong.

Is the example I have given correct, or is it wrong?

Why are you not taking any account of changing noise power?

But ok, i did another typo, yes QPSK is used in sat mod (90 deg shift,
not 180). Which doesn't change anything I said (but it would have been
wrong if I'd given a numerical example!).

I pointed out that "spectral efficiency" does not give complete
information. DTT COFDM is multicarrier, and also operates at much lower
SNR than QPSK, as satellite needs much higher SNR to cope with rain
attenuation etc (wait for rain, watch SNR go right down!).

Adrian wrote:
DAB sounds worse than FM wrote:
spiney wrote:
Unfortunately, "DAB" is wrong in most of what he says, as I shall
now show .....


Seeing as you've been talking nonsense up to now I doubt what you will
show will prove a thing.

I see that spiney is still posting, I'd hoped he'd gone as I hadn't seen
any replies to him for acouple of days.
--
Adrian A

Thank, Adrian. And your answer to my above question is ..... ?