fixing COFDM reception problems

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Mark Crispin wrote:
> Well, I found out how to get good COFDM reception on XM Radio: throw out
> the toy antenna sold with the set, and buy a professional grade
> satellite antenna (not sold in stores -- you have to special order it)
> with real antenna wire (not the cheap thin stuff).
>
> I have done so. The difference is like night and day.
>
> Hmm. A good antenna. Just like what fixes 8-VSB reception problems!
>
> So much for the people who claim that COFDM eliminates the need to have
> a good antenna.
>
> -- Mark --

A better antenna will not fix 8-VSB reception problems. 5th gen
technology goes a long way but 8-VSB falls far short of COFDM even then.

You might have noticed that XM and Sirius are in the 2332.5-2345 MHz
spectrum slice which is far more difficult that the TV spectrum below
800 MHz.

You might have noticed tht XM and Sirius didn't try to use 8-VSB
modulation they chose COFDM. Beleive me they didn't even consider 8-VSB.

NO one would for ANYTHING except in the charged political atmosphere of
the early DTV days in the US when back room deals that must be kept were
much more important that the best technology.

Now what an interesting thought. Try 8-VSB mobile in the 2332.5-2345 MHz
spectrum slice with a REAL GOOD ANTENNA!!! LOL!!!

The problem you were having with XM reception was probably in an area
with only a satellite signal which is not COFDM. IF you were in the
coverge area of one of their terrestrial broadcast COFDM repeaters you
would not need a fancy satellite antenna.

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On Thu, 14 Oct 2004, Michael J. Sherman wrote:
> Great, you just had to talk about COFDM. Now Bob Miller will no doubt
> respond with his usual drivel.

Anything that gets Bob Miller to discredit himself further is a good
thing.

-- Mark --

http://staff.washington.edu/mrc
Science does not emerge from voting, party politics, or public debate.
Si vis pacem, para bellum.

Archived from groups: alt.tv.tech.hdtv (More info?)

>So Bob Miller thinks that antennas have nothing to do with reception
>problems.

Yup. The same BOB who thinks that facts have nothing to do with the truth. He
is indeed our resident snake oil salesman who comes out to prey on the
ignorant.

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Seth Mattinen wrote:
> On 2004-10-13 22:42:44 -0700, Bob Miller <robmx@earthlink.net> said:
>
>> The problem you were having with XM reception was probably in an area
>> with only a satellite signal which is not COFDM. IF you were in the
>> coverge area of one of their terrestrial broadcast COFDM repeaters you
>> would not need a fancy satellite antenna.
>
>
>
> I am in the range of a Sirius repeater and I still have reception
> problems from time to time; far more than with my flawless OTA HDTV
> reception.
>
Maybe but give me your lat long and I will check it out.

If you want to compare COFDM to 8-VSB reception you have to first be in
the same area of the spectrum. Sirius is in 2.3 Ghz while OTA DTV is in
UHF which only gets to 800 MHz. Major difference.

With the same power levels and in the same spectrum space COFDM blows
away 8-VSB.

Anyone who truly would have wanted the US digital transition to have
prospered over the last five years instead of stagnate as it has would
have strongly demanded the best modulation. Ignorance has ruled and we
have had a stagnate transition instead. What a waste.

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In article
<Pine.LNX.4.62.0410182320190.7756@shiva0.cac.washington.edu>,
Mark Crispin <mrc@CAC.Washington.EDU> wrote:

> Remember, whatever Bob Miller says, the exact opposite is true!
>
> Bob Miller thinks that better antennas have nothing to do with quality of
> reception!

He also conviently neglects that many transmitters are currently
operating at reduced (often 15% or so) power.

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Bruce Tomlin wrote:
> In article
> <Pine.LNX.4.62.0410182320190.7756@shiva0.cac.washington.edu>,
> Mark Crispin <mrc@CAC.Washington.EDU> wrote:
>
>
>>Remember, whatever Bob Miller says, the exact opposite is true!
>>
>>Bob Miller thinks that better antennas have nothing to do with quality of
>>reception!
>
>
> He also conviently neglects that many transmitters are currently
> operating at reduced (often 15% or so) power.

Conveniently?? In most countries the "reduced power" you talk of in the
US is FAR above NORMAL power levels. For instance in the UK where they
have sold 5 million receivers in only two years (that would be 25
million in the US) the average power level of ALL transmitters is UNDER
ONE kW.

The highest powered transmitters in the UK are 20 kW and there are only
a few of them.

This is true around the world. And how ironic since 8-VSB proponents
argue that COFDM needs more power. It is 8-VSB that seems to need 1000
times the power of normal COFDM transmitters and still 8-VSB has problems.

With 5th gen 8-VSB receivers, designed with the lessons of COFDM in
mind, for the first time decent reception is achieved in a fixed
position. And a simple loop antenna taped to a bedroom window without
regard to orientation at ground level was able to do better than a
rooftop yagi with rotor. This was in a heavy old growth woods of a
subdivision behind a hill 22 miles from Manhattan.

Most problems people have been having with 8-VSB anywhere within 25
miles of an 8-VSB transmitter had to do with multipath and NOT the
antenna being used OR the power levels of the station.

Archived from groups: alt.tv.tech.hdtv (More info?)

Tim Keating wrote:
> On Wed, 13 Oct 2004 22:01:31 -0700, Mark Crispin
> <mrc@CAC.Washington.EDU> wrote:
>
>
>>Well, I found out how to get good COFDM reception on XM Radio: throw out
>>the toy antenna sold with the set, and buy a professional grade satellite
>>antenna (not sold in stores -- you have to special order it) with real
>>antenna wire (not the cheap thin stuff).
>>
>>I have done so. The difference is like night and day.
>>
>>Hmm. A good antenna. Just like what fixes 8-VSB reception problems!
>
>
> Sounds like you fixed the SAT reception aspect.
> Thus negating the need to pickup the unreliable COFDM signals.
>
> XM radio SAT broadcasts use QPSK modulation..

The ONLY reason XM radio has a terrestrial COFDM network in and around
most cities is because of the UNRELIABLE satellite QPSK signal.

Three different ventures are working on terrestrial only mobile COFDM
DTV networks in the US. When they are completed in the 700 MHz spectrum
all other forms of broadcasting will be in jeopardy. That includes
cable, satellite, AM/FM radio, terrestrial broadcasting using 8-VSB and
satellite radio both Sirius and XM.
>
> see..
> http://spacecom.grc.nasa.gov/icnsc [...] arneth.pdf
>
>
>>So much for the people who claim that COFDM eliminates the need to have a
>>good antenna.
>
>
> Just about any broadcast signal/format will be improved by using a
> better antenna.

A better antenna, the definition is where it gets tricky. A large
rooftop Yagi with rotor was not the better antenna on Long Island 20
miles from NYC in a woods behind a hill. The "better" antenna was a $2
loop scotched taped to a first floor bedroom window. It was never
touched after being taped. No orientation at all.

I think that we will find that up till now 90% of the problems with
reception will have been multipath when people start getting 5th gen
receivers.

Now maybe there is a better antenna than the loop but who cares the loop
brought in all stations that could be identified on a spectrum analyzer
at the site.

In a different circumstance the Yagi might be better like at 50 miles.
But at 20 miles the loop was the best.

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On Wed, 20 Oct 2004, Bob Miller wrote:
>> He also conviently neglects that many transmitters are currently operating
>> at reduced (often 15% or so) power.
> Conveniently?? In most countries the "reduced power" you talk of in the US is
> FAR above NORMAL power levels.

That is because in North America, we expect a TV station to cover a radius
of 75 miles or more.

In the other countries that you refer to, a station only covers a single
city or even a ward of a city. Most foreign TVs don't have channel
numbers; they just have a set of pushbuttons that are programmed once to
the frequences of the local stations and ignore further-away stations
(which just duplicate a local station).

Most of these countries are also far more densely packed than North
America, consider TV to be strictly an urban service, and have far fewer
distinct program channels than North America. London only has about a
half dozen channels. By comparison, much-smaller Seattle has 14 analog
channels.

If we followed the European system of low-power transmitters, we would
have TV towers in every city, suburb, small town, and rural village, and
only a handful of channels in any one place.

You know all this, but continue to lie. If 8-VSB was replaced with COFDM
at current power levels, much less European power levels, digital TV would
reach far fewer households in the US than it does today. COFDM does not
travel as far as 8-VSB.

-- Mark --

http://staff.washington.edu/mrc
Science does not emerge from voting, party politics, or public debate.
Si vis pacem, para bellum.

Archived from groups: alt.tv.tech.hdtv (More info?)

On Thu, 21 Oct 2004, Tim Keating wrote:
>> Hmm. A good antenna. Just like what fixes 8-VSB reception problems!
> Sounds like you fixed the SAT reception aspect.
> Thus negating the need to pickup the unreliable COFDM signals.
> XM radio SAT broadcasts use QPSK modulation..

Actually, the better antenna improves both satellite and terrestrial
reception. This can be seen in tunnels, and I had the opportunity to do
some fairly extensive tests.

In a city with no terrestrial (COFDM) signal, the better antenna held onto
the satellite signal longer than the original antenna before dropping out.

In a city with a terrestrial signal, the better antenna held onto the
terrestrial signal after the satellite signal was lost, whereas the
original antenna lost both.

The key point is that COFDM didn't save the day with a standard antenna; a
premium antenna was needed to keep the signal. Antenna quality is more
important than modulation.

Bob Miller's claim that Japanese households can receive COFDM-based
digital TV inside Faraday cage apartments using rabbit ear antennas is
ludicrous. I will soon be in Japan, and will personally test this claim.
I will report on the result, and what sort of antenna is recommended by
the vendors of digital TV in Japan.

-- Mark --

http://staff.washington.edu/mrc
Science does not emerge from voting, party politics, or public debate.
Si vis pacem, para bellum.