[opendtv] Re: DVB-T HDTV demo using 19.7 Mbps in a 6 Mhz channel in costa ri
- From: Mark Aitken <maitken@xxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Tue, 07 Mar 2006 10:30:01 -0500
For clarification to all...I think Doug is using his dB to reflect a
noise figure (NF), not GAIN.
In general terms, when one has an amplifier at the start of a system, as
long as that amplifier has GAIN of ~10dB (or more), it sets the noise
floor for the entire system (in an ideal world where other factors don't
crud things up...such as amplifier overload generated intermodulation
products, receiver front end overload [and its associated negative
byproducts], etc.). So, an amplifier with 10dB (or more) of GAIN, with a
noise figure of 0.6dB will have the ability to "see" a signal that is
weaker proportional to the larger NF of the receiver itself (~8dB
typically in a GOOD receiver, yielding a 7.4dB benefit). This is a
generalization, because one has to also take into account the absolute
effects of RF loss, the effects of impedance mismatches and their
relative phase(s), antenna characteristics [antennae do NOT have
identical characteristics at all frequencies], other sources of
interference and/or interference generating RF outside the band [FM,
cell services, etc.], and the list goes on....
I have maintained for many years, the biggest issue for Broadcasters is
that our business is NOT viewed as a complete service requiring the
provision of a complete system Just as one goes to a satellite service
provider and they provide the complete "system", Broadcasters need to be
doing the same. The ability to package (appropriately) the essential
elements of a complete system exists (technologically), but there does
NOT exist the technical business leadership for the industry to address
it cohesively.
That's my story, and I'm sticking to it!
Mark Aitken
frustrated with what he knows, and the industry REFUSES to address!
Doug McDonald wrote:
>Albert Manfredi wrote:
>
>
>>Stephen W. Long wrote:
>>
>>
>>
>>>If you are going to all of the trouble to have a 30' antenna,
>>>the selection of a 3db preamp to pull in a COFDM signal is no
>>>big deal.
>>>
>>>
>>It's not quiite that simple, right? The antenna amp might help compensate
>>for signal losses in the downlead and connectors, but it won't create 3 dB
>>of signal out of energy from a 115 VAC outlet.
>>
>>
>
>
>The 3dB or 0.6 DB preamp is to amplify the signal without
>adding noise. TV sets and STBs have crappy 6 dB or 8 dB
>preamps. In the far field you need a better one. Cable
>length does not matter much, since you need the good preamp
>even if the cable length is five feet.
>
>Doug McDonald
>
>
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--
><> ><> ><> ><> ><> ><> ><>
Regards,
Mark A. Aitken
Director, Advanced Technology
<>< <>< <>< <>< <>< <>< <><
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