[opendtv] Re: 20050727 Wolfsson's Wednesday Words (Mark's Monday Memo)

Tom Barry wrote:

>Mark Schubin wrote:

>>
>> - Non-masked Charlie Rhodes has an even more interesting piece in TV 
>>Technology.  Here's an excerpt:
>>      "This brings us to double conversion tuners like the type Zenith 
>>designed for testing its 8-VSB DTV modulation technology.  It was the 
>>outstanding interference rejection of that double-conversion tuner that 
>>led the FCC to conclude that the UHF taboos did not apply to DTV":
>> <http://www.tvtechnology.com/features/digital_tv/f_charles_Rhodes.shtml>
>>
>
>I've included that article here in hopes someone can explain it better. 
>Does it help or have implications in explaining the Zenith mystery 
>boxes tested at Mark's apartment?  And will the lack of double 
>conversion tuners mean we have to set aside extra channels to avoid 
>interference in some areas?
>
>- Tom

Charlie did a great job highlighting some of the trade-offs between single 
conversion, double conversion and direct (zero IF) conversion. There is, 
however, no "lack of double conversion tuners" in the marketplace. Particular 
TV makers choose single vs. double conversion for the usual reasons -- cost vs. 
performance -- and not all of them are using single conversion. Most tuners 
that are marketed as "DTV tuners" are in fact the double conversion variety. As 
single-chip "silicon tuners" continue to evolve and cost-reduce, the cost 
advantage of single over double conversion will approach zero.

There is no question that Zenith employed a high-quality double conversion 
tuner in its early 8-VSB receiver prototypes, and, I suspect, in all the 
receivers they have made since then. That doesn't prohibit other manufacturers 
from doing the same. I do not see evidence that the FCC was mistaken in 
concluding that UHF taboos do not apply to DTV -- ***after*** NTSC is shut off. 
Before that time, with a fully loaded NTSC+DTV spectrum, we truly have an 
interference nightmare. Good thing it is a temporary problem.

-- Frank

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