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 > >>> > >>> > >>> > >>> > > > > > ---------------------------------------------------------------------- > You can UNSUBSCRIBE from the OpenDTV list in two ways: > > - Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org > > - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line. > > ---------------------------------------------------------------------- You can UNSUBSCRIBE from the OpenDTV list in two ways: - Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line.