Re: Croiset claims 4 = 1

Nicolas Croiset wrote:
"DAB sounds worse than FM" <dab.is@dead> wrote :



VHF aerials will give something like 8 or 9 dB in high power
installations (using up more tower space than a typical DAB system
does, count on 12 meters). This gain will of course be the same for
DMB and DVB (or analog TV or anything else at that frequency for
that matter).


If they've got the same amount of space you can work out the
difference in aerial gain by comparing the number of aerials they
can get in a given amount of space, and the number of aerials is
proportional to the aerial gain (linear gain, not decibel):

Say you've got X metres of space, so you'd have

Number of antennas = X / antenna length = X / half-wavelength

So say they've got 10m of space each, at 500 MHz there'd be room for
(ignoring spaces between antennas, because it's theoretical anyway):

Num antennas = 10 / (3 x 10^8 / 500 x 10^6) = 16 antennas

At 200 MHz there'd be:

Num antennas = 10 / (3 x 10^8 / 200 x 10^6) = 6

So aerial gain due to number of antennas at UHF relative to Band III
is:

10 log (16 / 6) = 4.2 dB

This is partially wrong, because you forget the loss of the feeder
which are higher in band IV/V than band III...


It would be, wouldn't it.


When you have one transmitter every 1km you don't have the same place
as on a big mast, so the antenna gain is largely lower, so this
assertion is not true.


1 transmitter every 1 km? Are you drunk?


It would seem that DMB could only be implemented in L-Band, as band
III is full. DVB-H could be implemented in the space to be sold as
part of the "digital dividend", sharing its infrastructure with
DVB-T. So perhaps the calculations should be comparing about 600 Mhz
with 1500 :-)


Absolutely! But to be honest I'm more interested in getting Croiset
to finally admit that he was talking nonsense about DVB-H vs DAB/DMB
in Band III.

But doing the DVB-H/UHF vs DMB/L-band comparison, the field strength
values are:

DVB-H/UHF (3.74 Mbps) = 100.7 dBuV/m
DVB-H/L-band (2.33 Mbps) = 104.2 dBuV/m

T-DMB/L-band (1.06 Mbps) = 105.4 dBuV/m

You just forget to add the this information:

DVB-H/L-band (2.33 Mbps) 5MHz = 104.2 dBuV/m
T-DMB/L-band (1.06 Mbps) 1.7MHz = 105.4 dBuV/m

DMB : 062 bit/Hz/s
DVB-H : 0.466 bit/Hz/s

You spoke a lot of time about the efficiency of DVB-H and now you
don't say anything.


I spoke a lot about the efficiency of DVB-H for carrying digital radio
stations in Band III instead of the ultra-inefficient DABv1 system. So let's
try that, shall we?

Using figures from the EBU document:

DVB-H: 3.27 Mbps per mux at 88.2 dBuV/m
T-DMB: 1.06 Mbps per mux at 88.0 dBuV/m

And DVB-H uses AAC+, which is about 3-times as efficient as MP2. So, for
virtually identical transmitter power levels, the following number of radio
stations can be carried on DAB and DVB-H:

For 56 kbps AAC+ providing the same level of audio quality as 160 kbps MP2:

DVB-H can carry 3270 / 56 = 58 stations per 7 MHz multiplex
DAB can carry 8 stations per 1.7 MHz multiplex

So, for virtually identical transmitter power levels, DVB-H can carry
7-times as many stations as DAB can.

And in terms of number of stations per MHz:

DVB-H can carry 58 / 7 = 8.3 stations per MHz
DAB can carry 8 / 1.7 = 4.7 stations per MHz

AND the above figures are giving DAB the advantage of using RS coding, when
in fact DAB does not use RS coding, so the actual figures would be
significantly better for DVB-H than they actually are.

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

Find the cheapest Freeview & DAB prices:
http://www.digitalradiotech.co.uk/freeview/freeview_receivers.php
http://www.digitalradiotech.co.uk/dab/dab_radios.php


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