Re: Croiset claims 4 = 1

• From: "DAB sounds worse than FM" <dab.is@dead>
• Date: Sat, 03 Feb 2007 18:04:32 GMT

hwh wrote:
DAB sounds worse than FM wrote:
hwh wrote:
DAB sounds worse than FM wrote:
Other than that, the highest DVB-H transmitter I could find is 80
kW covering the whole of Greater Sydney:
And a typical UHF high-power transmitting aerial can give 10-13 dB
or more of gain (taking up 10 to 18 meters of tower space).

Excellent point! So the 12.7 dB difference in ERP would actually be
around zero! Is 10-13 dB extra aantenna gain with respect to Band
III usual?

No, the quoted figure is relative to a hypothetical aerial with no
gain (isotropic radiation). I did not say that the 10-13 dB was
relative to band III.

Okay.

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

BTW, what's your opinion of Croiset's claim that DVB-H would have to
use ERPs in the region of 10 MW to 28 MW? ;-)

Both systems have their advantages. The power use will not decide
which system is going to win, marketing and content will.

True, and DVB-H has basically already won, because you just have to look at
the number of countries using it or planning on using it.

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

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

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