[opendtv] Re: 7" ATSC TV

That's basically what I said, these problems can be satisfactory resolved
using some combination of wide band AGC, multi conversion IF and tracking
filters. With a tracking filter and wideband AGC, a receiver can perform
adequately without dual conversion and there are clearly other possible
designs. However, a special effort is required to achieve satisfactory
performance at the level required when operating in packed RF environments.

If I somehow implied a belief that each manufacturer constructs their own
tuner, that was not my intention. I know that packaged tuner/demodulators
are OEM purchased from a few manufacturers. However, That does not release
the set manufacturer from any responsibility for their sets poor receiver
performance.

> -----Original Message-----
> From: opendtv-bounce@xxxxxxxxxxxxx
> [mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Allen Le Roy Limberg
> Sent: Monday, April 23, 2007 6:11 AM
> To: opendtv@xxxxxxxxxxxxx
> Subject: [opendtv] Re: 7" ATSC TV
>
>
> Dale Kelly's e-mail seems to assume a TV industry that no longer exists.
> Many television set manufacturers do not use integrated circuits of their
> own design and manufacture in their sets.  Rather a chipset from a silicon
> foundry is purchased for installation.  ATI and Broadcom are two
> well-known
> domestic sources for DTV IC's, and they supply many setmakers.
>
> Single-conversion front-ends are less afflicted with phase noise than
> dual-conversion front ends.  Dual conversion improves image rejection,
> rather than suppressing third-order IM.  Back in 1936 or so
> Clarence Hansell
> invented an image-rejection technique for single-conversion receivers that
> was costly for vacuum tube days.  The technique recently has
> appeared in DTV
> receiver designs.  Balanced mixers can help.
>
> One "secret" to keeping IM within bounds is to use wideband AGC
> on the first
> converter and RF amplifier, rather than narrowband delayed AGC
> delayed from
> IF amplifier AGC.  This is a technique developed by Hallicrafter
> radio back
> before WWII and touted in recent years by Charlie Rhodes.
>
> Al Limberg
>
>
>
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