[opendtv] Re: Latest S/N test
- From: "Allen Le Roy Limberg" <allimberg@xxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 27 Jan 2005 10:11:31 -0500
The problem with dual-conversion receivers for DTV is phase-modulation-noise
from the oscillators used in the early mixers. The phase modulation is
greater the higher the frequency of the local oscillations.
Front-end overload problems are alleviated by using wideband AGC on the RF
amplifier and first mixer, rather than delayed AGC developed from the
narrowband AGC used on the IF amplifiers. The use of wideband AGC on the RF
amplifier and first mixer was used in Hallicrafter receivers during WWII,
Charles Rhodes told me a few years ago. I hear via the grapevine that he
has recently authored a paper on the matter. Oded Bendov and C. B. Patel
recently wrote a paper "Television Receiver Optimization in the Presence of
Adjacent Channel Interference" for the IEEE Transactions on Broadcasting,
but I am unsure whether it has been published yet or will soon. My U.S.
patent application 2003-0007103 publishe 9 January 2003 and titled "DIGITAL
TELEVISION RECEIVER WITH REMOTE TUNER FOR DRIVING TRANSMISSION LINE WITH
INTERMEDIATE-FREQUENCY SIGNAL" describes wideband AGC to avoid overload of
the RF amplifier and first mixer in the remote tuner located at the antenna
site.
Al
----- Original Message -----
From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
Sent: Wednesday, January 26, 2005 4:14 PM
Subject: [opendtv] Re: Latest S/N test
> Dale Kelly WROTE:
>
> > RF interference and other related distortion
> > issues also greatly impact channel S/N performance
> > and tend to be overlooked. The attached URL is for
> > one of a series of articles written on the subject
> > by the highly regarded engineer, Charles Rhodes. I
> > believe you will find this and his other relates
> > articles of interest.
> >
> > =
> http://www.tvtechnology.com/features/digital_tv/f_DTV_interference.shtml
>
> Thanks, Dale. Excellent article.
>
> I thought that dual conversion tuners were designed
> specifically to combat intermodulation (and
> cross-modulation?). Which is why I was surprised to
> see a couple of recent press releases, where the
> manufacturers were touting their single-conversion
> chips as being something great. Maybe great, but
> mainly for cost reasons, no?
>
> I guess you have to watch out for those more
> obscure performance measures, such as this third
> order intercept power. Maybe that's one reason
> the LG 5th gen does so well, even with all those
> analog stations still on the air.
>
> Bert
>
>
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