[opendtv] Re: 5th generation Test

  • From: dmenolan <dmenolan@xxxxxxxxxxxxxx>
  • To: Open DTV list <opendtv@xxxxxxxxxxxxx>
  • Date: Thu, 17 Mar 2005 03:48:17 -0500

In 1998 the first COFDM box, the Philips 6370, had to have an attenuator =
(6-9dB) fitted in line to make it work in the presence of very strong adj=
acent channel analogue signals. The design of that receiver did not have =
sufficient selectivity. Experience from that unit, SEVEN  YEARS AGO, was =
factored straight into the design of COFDM boxes. Nowadays even the el ch=
eapo COFDM boxes have fantastic receiver RF performance because they have=
 to. And there is a further development which will seriously impact DVB-T=
: because of the coming of DVB-H it is necessary to have a system on a ch=
ip with full digital RF eg Texas Instruments forthcoming DVB-H chip. Thes=
e chips will have outstanding RF performance because they have to in the =
mobile environment. DVB-H is backwards compatible with DVB-T. Several IC =
vendors have told me that expect only to be making DVB-H chips in a coupl=
e of years time: so DVB-T receivers will benefit from this digital miniat=
urisation. Full details are on the TI and Dibcom web site. So now we have=
 ATSC trying to fix receiver selectivity problems which were fixed in sec=
ond generation COFDM boxes: maybe by generation 12 they will catch up wit=
h COFDM year 2000 receiver performance. A sorry saga continues..

Kind Regards,

Dermot nOlan
-------------Forwarded Message-----------------

From:   INTERNET:opendtv@xxxxxxxxxxxxx, INTERNET:opendtv@xxxxxxxxxxxxx
To:     , INTERNET:opendtv@xxxxxxxxxxxxx
        =

Date:   16/03/105 18:07 PM

RE:     [opendtv] Re: 5th generation Test

 =

Doug wrote:
> It's now time to try the el-cheapo 5th generation box with
> a really good single-channel filter (Blonder-Tongue?)
> in front of it for the difficult channels. If it really is the
> front end, that should make it work.

Bob, this is very good advice from Doug.
Hammett & Edison's use of a prefilter turned the early poor
performing RCA TC100(?) receiver into a moderately good
performer in their San Francisco tests. Also, Sinclair used a
similar technique on the "failed" COFDM monitor/receiver
used in the MSTV tests, turning it into a stellar performer.
Unfortunately, MSTV/NAB didn't want their results confused
by fact and summarily rejected Sinclair's findings. As I recall,
that filter was about 40 MHz wide (about six channels).

Without the proper use of selectivity, a DTV receiver doesn't stand
much of a chance in congested RF environs.

----- Original Message ----- =

From: "Doug McDonald" <mcdonald@xxxxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Tuesday, March 15, 2005 9:29 AM
Subject: [opendtv] Re: 5th generation Test


> Manfredi, Albert E wrote:
>
>> Dale Kelly wrote:
>>
>>
>>>As I previously suggested might be the case, it appears
>>>that Zenith utilized a specially designed RF front end
>>>in the receiver used for  the 5th Gen demonstrations -
>>>possibly never to be seen again in a consumer product.
>
>
> It's now time to try the el-cheapo 5th generation box with
> a really really good single-channel filter (Blonder-Tongue?)
> in front of it for the difficult channels. If it really is the
> front end, that should make it work. It could also
> be something else, like the chip allows different amounts of
> external memory, or uses aid from the main box CPU, and
> these were lacking in teh cheapo box.
>
> Doug McDonald
>
>
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Date: Wed, 16 Mar 2005 10:07:02 -0800
From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
Subject: [opendtv] Re: 5th generation Test
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