[opendtv] Re: First look at ATSC HD Broadcast
- From: Bob Miller <bob@xxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sat, 11 Jun 2005 22:12:04 -0400
Let the full story be told. Before the test began I offered a Victor
Tawil our help in supplying or procuring 6 MHz COFDM receivers. He
informed me that they had all they needed. I offered to participate with
and to help in anyway since we had been testing COFDM receivers and had
trapsed all over Europe talking to those making receivers. He didn't
need any help.
They had carefully found an obscure British company who didn't have a
clue as to what was going on and disregarded written instructions on
using a front end filter. They didn't say anything to this company about
what they were testing.
This test was being conducted by top US engineers from the FCC why would
they not know what to ask for? How to ask for it?
I give them the benefit of the doubt. I think they were profesional
engineers well educated in RF technology and I think they knew EXACTLY
what to ask for and from whom to ask it.
Here is what BT had to say about the request that was copied to Victor
Tawil.
Bob Miller
BROADCAST TECHNOLOGY LTD
Sopwith Park
Royce Close
West Portway Industrial Estate
Andover
Hampshire
SP10 3TS
United Kingdom
Tel: +44 (0)1264 332633
Fax: +44 (0)1264 334509
E-mail: btech@xxxxxxxxxxxxxx
Website: http://www.btl.uk.com
Registered Number 2143040
Registered Office: 26a High St, Andover, Hampshire, SP10 1NN
Date: 22/1/2002
Ref: NJ/IK
Lynn Caudle
Senior Vice President, Science & Technology
National Association of Broadcasters
1771 N Street,
Washington
DC 20036
United States of America.
Dear Mr. Caudle,
As Managing Director of Broadcast Technology Limited, I would like to
make a statement of fact regarding the Broadcast Technology Ltd (BTL)
DVTM2000(T) Digital Terrestrial Transmitter Monitors used in the
recently concluded “Phase I” comparative testing of the MSTV/NAB -
VSB/COFDM Project. It has come to my attention that my company’s product
is being blamed for providing less than optimal performance. The fact is
that our product was used in a manner for which it was not designed nor
intended, and the result of this misguided use has lead to misleading
results and incorrect conclusions. In a single sentence, the integrity
and validity of the data collected using our products in an un-protected
terrestrial receiving environment inconsistent with its intended use can
be dismissed as being irrelevant at best.
The DVTM2000(T) product line, as indicated by the product title, is a
series of professional products offered for the monitoring of DVB-T
COFDM transmitter performance and emissions. Part of this monitoring
includes the ability to accurately record and reproduce the frequency
response spectrum of a transmitter. Monitoring receivers must in no way
impair or “colour” this response. It is for this reason that our
monitoring grade units have wideband input. General reception receivers,
on the other hand, need to have frequency selective inputs in order to
reject any high level “off
channel” signals. However, to achieve this selectivity, tracking filters
that work over a range from 55MHz up to 850MHz have to be used. These
filters introduce distortions that can cause rounding or tilt of the
received signal.
The DTVM(T) was not designed nor intended to operate in the harsh and
open world of an out-of-doors terrestrial receiving environment. Such
operation is possible, but possible only by taking prudent steps such as
providing proper channel pre-selection filtering, and maintaining proper
signal levels at the equipment inputs. For the purposes of field trials
or monitoring, as opposed to transmitter measurement, a new version of
the DTVM 2000, with selective input has been under development. This
unit would have been infinitely more suitable for the trials that have
recently been undertaken.
When in mid 2000, BTL was contacted by US organisations requesting it to
provide equipment that would be used in conjunction with a series of
comparative tests of DVB-T’s COFDM and the US ATSC 8VSB technologies, we
proudly responded to this request by providing five (5) of our
transmitter monitors for testing purposes. The nature of such testing
requires an understanding of many separate engineering
disciplines and techniques, and implies that measures to insure proper
operation are being provided for equipment applications by qualified
personnel. These steps were not taken.
2.
It is hardly surprising to me and my engineers, now fully understanding
the nature of the testing performed, that erroneous results were
obtained regarding DVB-T COFDM reception capabilities in multiple
locations using our transmitter monitoring equipment. It is our combined
professional opinion that the results obtained while operating our
professional product in the environment now stated as being a direct
antenna connected environment with various FM, Low VHF & High VHF,
multiple high power UHF, land-mobile and cellular communications
existing, are totally without merit. Had we been made fully aware of the
nature of the testing at the time of the original request for equipment,
and the RF
environment our equipment was to be operated in, we would have made
specific recommendations to include channel pre-filtering or acquire
other equipment more appropriate to the needs.
As a respected provider of quality professional equipment to the
Broadcast industry, we stand by our products and the performance
provided when operated in a manner consistent with the products design
parameters. The particular product chosen for this important comparative
test, the DVTM2000(T) Digital Terrestrial Transmitter Monitor, was not
designed to operate under the difficult and challenging conditions
which were chosen. Under these circumstances we would have recommended
an alternative version. Data collected without proper pre-selective
filtering will be subject to failure in many of the environments we
understand to exist. Tabulation of results will indicate failures due to
inappropriate operation, not failures of the transmission system. Once
again, the integrity and validity of the data collected using our product in
a direct antenna connected terrestrial receiving environment can be
dismissed as being irrelevant and speculative at best.
We hope that the above will clarify the situation and would be pleased
to answer any questions that might arise.
Yours sincerely,
Nicholas Jennings
Managing Director
Broadcast Technology Ltd
Copy to: Victor Tawill Sen.VP MSTV.
John Golitsis wrote:
>And just so the full story is re-told, that "receiver" was offered by the
>manufacturer as one that would fit the needs of the testing. We all read
>the official request, and the official reply, and the manufacturer failed to
>make any mention at all of it's need for front end filtering. Nor did
>Sinclair who was in possession of the receiver before it was passed on to
>the NAB.
>
>Of course, AFTER the testing was completed is when this all came up. How
>bloody convenient.
>
>----- Original Message -----
>From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
>To: <opendtv@xxxxxxxxxxxxx>
>Sent: Saturday, June 11, 2005 1:37 PM
>Subject: [opendtv] Re: First look at ATSC HD Broadcast
>
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