Re: [IRCA] "HD" DX?

[Barry McLarnon <bdm@xxxxxxxxxx>]

On Tuesday 09 January 2007 00:30, Craig Healy wrote:
> > Barry, you and Craig Healy are the only reports I know of
> > that have had any HD audio..
>
> Mine was just a few seconds of WOR-710 (150 miles).  Some time back
> WOWO-1190 left the IBOC on overnight.  I had some paperwork, so I put the
> JVC in digital-only and let it sit.  It was at least an hour, maybe two.
> Not a peep of audio.  Same with WHAM-1180 when they left theirs on.  Let it
> run for a long time, no HD digital audio at all.

Okay, I'll withdraw my claim of first skywave digital audio - now, you and 
Powell can fight over it. :-)

> Local groundwave tests show half or less the radius of good-quality analog
> reception.  No noise behind the analog.  If WHJJ-920 is a 30+ mile analog
> signal, the HD is tapped out at under 15 miles.  FM shows a similar half
> radius limit.  What that means is that it takes a bootload of signal
> strength before HD can decode.  Probably more than skywave can really
> deliver.  I should try WTWP-1500 and WDCD-1540 at sunset.  Those might be
> the best chance, though the adjacents to 1500 are problematic, and 1540
> fades a lot as it's very close to here.

A big margin (at least 25 dB or so) over 1st adjacents is a necessity, and 
that can be hard to come by when the skywave is in.  My limited success with 
WDCD came quite early (a few minutes past local sunset), before stations such 
as WCKY-1530 and CBE-1550 had built up in strength.  It interesting to note 
that in a lab environment, the digital audio could be decoded in the presence 
of strong 1st adjacent interference on one side, as long as the other primary 
digital sideband had no significant interference to contend with.  However, 
this tolerance for one-sided interference doesn't seem to carry over into the 
real world very well.  If AM IBOC nighttime operation is ever allowed (which 
is looking increasingly unlikely at this point), the digital groundwave 
coverage at night will be truly pathetic.  And skywave coverage, of course, 
will remain nil.

Barry

-- 
Barry McLarnon  VE3JF  Ottawa, ON
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