[opendtv] Re: 7" ATSC TV
- From: "Allen Le Roy Limberg" <allimberg@xxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 23 Apr 2007 09:11:20 -0400
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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