Re: [IRCA] IBOC TIME LAG

["Bob Foxworth" <rfoxwor1@xxxxxxxxxxxxxxx>]

If I were designing a $500 dollar radio I'd make it a $510
dollar radio and include some sort of wideband test point
in the RF chain so that a scope could be put on, to look
for signal distortion effects that would make decoding
not happen. It can be as simple as a buffer amp feeding
a BNC-type jack behind a small panel on the chassis.

I'd be very interested to know if such exists in the receivers
now being sold. This should be part of the shake-down
design process. These are the first wide-scale deployments
of rcvrs in the field, not under the direct control of those,
such as iBiquity, who have a vested interest in the outcome
of the testing. There is the potential to gather a lot of
useful data on night HD that is probably being ignored,
because non-technical managers are ignoring it.

There must be a reason that Craig can't get a decode of WOR
in Providence when the analog is so good. Is there some
sort of time separation of two different hops, arriving slightly
out of phase, maybe by just a few data bits' separation,
causing some cancellation effects that would not be audible
in analog? Is there a way to look at the RF envelope and
test for this?

More importantly, do the designers of HD even anticipate this,
have they determined that this is a non-issue for testing,
or do they know of it and write it off as something not worthy
of thought?

If it is shown that WOR can't decode reliably in an area as
close as Providence, when WOR has high power, a low
dial position (presumably a more stable E-layer hop)
and relatively high d/u signal ratio, what will happen when
trying to decode a 5 or 10 kw at the top of the band, with
much more background chatter and a more variable
E-layer hop which could cause selective fading inside the
digital sidebands? And how much into the primary area
coverage will this occur?

The FCC rulemaking seems to allow for a binary choice
of day/night mode, but the diurnal transition can make all
this problematic.

Another question is whether there are differences in
implementation at various stations, such as sideband
level, that affect how the receivers do the decode.
The scope envelope output could help test for this.

I would have thought the HD designers would be anxious
for feedback from the field on these questions, as it is
just now becoming available. Sad to think that it is
very unlikely any of them will ever even read this.

I realize that the WOR management would be expected
to say that they are not interested in this market, however
I feel that it is necessary to do the research, and that there
will be other implementors that ARE interested..

- Bob
1033 est



> On WBZ the digital audio is a full 8 seconds behind the analog, which
is
> real time.  The analog audio is supposed to be delayed so there is a
time
> sync between the two.  However, WBZ relies heavily on off-air cues for
> traffic and field reporters so it has been impossible for them to do
this.
> They are looking at a different feed and receiver system to fix this
for
> their talent.  My guess is that they are banking on there being so few
> receivers out there that nobody notices.  Or, they feel that they have
> enough signal that it will be digital all the time.  On point 1 they
may be
> correct.  On point 2 they are wrong.  Bridges and local interference
are
> enough to shunt it back to analog, with the expected garble of
continuity.
> I've noticed the ignition interference in my truck causes a coverage
hit,
> and that truck has been modified to be pretty quiet.  Even some noisy
> traffic light controllers cause problems.
>
> If the JVC is left in "auto", it jumps back and forth.  In locked
digital,
> it simply dies out.  In analog it's just another radio.
>
> WHJJ has the audio synchronized properly.  On FM, WZLX has the 8
second
> difference, while WMJX is correct.
>
> Yes, there is a delay.  I believe Tom Ray said he has advanced the
WOR-710
> TOH time pip so theirs is correct.  I can't tell as the WOR IBOC
signal
> stubbornly refuses to decode, even after dark here.  Despite loops,
despite
> longwires, amps and tuners.  Nada.  Odd, really.  At sunset WOR is
really
> strong in Providence.
>
> Craig Healy
> Providence, RI

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