[opendtv] Re: Latest S/N test

  • From: "Allen Le Roy Limberg" <allimberg@xxxxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Thu, 27 Jan 2005 17:18:58 -0500

RF tracking filters for the various bands generally use varactor diodes in
their construction.  They employ inductors as well, so they are discrete
electronics.

----- Original Message ----- 
From: "Ron Economos" <k6mpg@xxxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Thursday, January 27, 2005 3:58 PM
Subject: [opendtv] Re: Latest S/N test


> Rhodes' current column is now on the website
>
>
http://www.tvtechnology.com/features/digital_tv/Features_Rhodes-01.19.05.shtml
>
> Ron
>
> Dale Kelly wrote:
>
> >Allen wrote:
> >
> >
> >>The problem with dual-conversion receivers for DTV is
> >>phase-modulation noise
> >>
> >>
> >
> >What is the trade off between this increased phase noise and it's ability
to
> >reduce destructive image signals - considering our tightly packed DTV
> >spectrum's unimpeded usage of high powered taboo channel assignments? A
> >single conversion receiver must also deal with this serious issue - how,
> >other than thru good AGC design?
> >
> >
> >
> >>Front-end overload problems are alleviated by using wideband AGC on the
> >>RF amplifier and first mixer.
> >>
> >>
> >
> >I agree, good AGC performance is critical and I seem to recall some *much
> >older* receivers having uncoupled dual AGC stages (RF/IF).
> >It occurs to me, however, that an unfiltered wideband RF AGC operating in
> >our
> >hostile RF environment could allow strong undesired signals to set the
> >amplifiers gain, thereby reducing the C/N of the desired signal (a
condition
> >which resulted in the COFDM receivers poor performance during the MSTV
> >tests). Is not preselectivity needed in a receiver designed for it to
> >perform
> >acceptably in the current and future RF environments?
> >
> >In such maters I certainly defer to the knowledge of CB, Oded, Charley
and
> >yourself. During the last couple of years CB and I have engaged in
numerous
> >highly instructive discussion regarding DTV receiver design issues but I
am
> >clearly a novice. There are very few left who truly understand this
*art*,
> >other than those who you mentioned.
> >
> >
> >
> >----- Original Message ----- 
> >From: "Allen Le Roy Limberg" <allimberg@xxxxxxxxxxxx>
> >To: <opendtv@xxxxxxxxxxxxx>
> >Sent: Thursday, January 27, 2005 7:11 AM
> >Subject: [opendtv] Re: Latest S/N test
> >
> >
> >
> >
> >>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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