Manfredi, Albert E wrote:
They do not have a subset for hand-helds AFAIK. Reception is supposed to be better than DVB-T but not as good as DVB-T with diversity reception. That is comparing DVB-T with diversity to CDMB-T/H without.Bob Miller wrote:
China was going to go with a dual standard but took some time
and come up with a compromise which incorporates some of the
VSB stuff but is still a multi-carrier TD-OFDM modulation.
Broadcasters are not going to be using a single carrier for
rural areas and a multi-carrier for cities. I think the VSB
part is more face saving to get this done. Notice no one is
talking about dual receivers or broadcasters having to chose
what modulation to use anymore which they were doing in the
summer.
Problem is, Bob, I can't tell how much of this is fact that you are reporting, and how much is your repeated editorial comment on VSB.
The article could be completely wrong, of course. But as written, the article states clearly that VSB is used to fixed sets, in cities or in rural areas, and that time-synchronous COFDM is used to handheld devices, in cities. Presumably, there won't be a lot of coverage in rural areas for handheld devices, since that requires a rather dense distribution of towers.
Just like in the US and Europe, broadcast transmissions to handhelds and to fixed sets are different. Different programming. So there's no reason to expect dual-mode sets, although of course in principle that should be possible. In China or elsewhere.
I was hoping that China would have a dual standard and that their much improved VSB based modulation would go head to head with their TD-OFDM modulation in the marketplace. I was not talking about some formal test between the two. They have only chosen CDMB-T/H as a standard for terrestrial DTV and it is designed to work mobile. I don't know of any other modulation that they have adopted for anything nor do I know of any formal test of any modulation.I thought it would have been interesting to see them go head
to head and was disappointed when they compromised. The VSB
had mobile test in one city and fixed in some others but the
DMB-T test were taking place in 30 or more cities. If they
had gone head to head no one would have implemented the VSB.
But again, are you reporting that you know for a fact that VSB was not tested against COFDM at any time? Note that if they already chose TS-COFDM as a service for handheld devices only, by this summer the only comparison tests that would make sense would be against DMB-T. Not against the unrelated VSB signal.
On a slightly related note, last night I finally managed to receive WETA-DT (local DC PBS station, low power, adjacent to high power analog WETA-TV). Very marginal signal. Probably because the analog station was off the air at that late hour. No such luck again this afternoon, though.
This is as much fun as playing with shortwave radio when I was a kid.
Bert
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