[opendtv] Re: Latest S/N test
- From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 27 Jan 2005 14:41:19 -0800
> RF tracking filters for the various bands generally use varactor diodes in
> their construction. They employ inductors as well, so they are discrete
> electronics
I assumed as much from past experiences but didn't know what recent
miracles might have occurred!
----- Original Message -----
From: "Allen Le Roy Limberg" <allimberg@xxxxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Thursday, January 27, 2005 2:18 PM
Subject: [opendtv] Re: Latest S/N test
> 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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