[opendtv] Re: Latest S/N test

Ron Economos wrote:

> Rhodes' current column is now on the website
>
> =
http://www.tvtechnology.com/features/digital_tv/Features_Rhodes-01.19.05.=
shtml

And, right on topic, in it he states:

"This brings us to another great unknown: What will
the RF selectivity be of future receivers built under
FCC's DTV tuner mandate? In some cases, RF selectivity
may be nothing more than switchable bandpass filters,
Channels 2-6, or 7-13 or 470-806 MHz.

"A better solution is a tracking, tunable RF filter,
but the problems of such filters include the physical
size of the inductors, the costs of factory alignment,
the Q factor of the resonant circuits and the small
fractional bandwidth desired at UHF (1 percent).

"Zenith understood these problems well enough to use a
double-conversion tuner, but it too has problems with
noise and cost.

"I understand that most DTV receivers have single
conversion tuners. Will DTV tuners have tracking or
bandpass filters next year?"

If by "Zenith" Rhodes means the 5th gen LG, then
evidently the noise/selectivity tradeoff favors
dual conversion tuners. At least, as of now. I now
wonder how sensitivity measures in the 5th gen LG.

If this third order interference created within the
receiver is a function of the cube of input power,
seems to me that regular old single converion tuners
without some other provision to increase selectivity
are not going to do well. Even wide band AGC might
not help. A weak channel surrounded by loud ones
can easily drop below the 15 dB margin in this sort
of case, yes?

Bert
 
 
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