[time-nuts] WWVB format change in 2012

[Martin Burnicki]

Bob Camp wrote:
> Hi
> 
> WWVB and WWV (like any radio uncorrected radio system) has fairly predictable shifts
> associated with the day / night ionosphere. One *could* fix that issue with a table
> based on station location. I do not know of any library of code that does that already. 
> 
> The next “layer” of trouble comes from how the low cost receivers are implemented. The
> common issue is local noise. The common solution is a narrowband crystal filter in front
> of the receiver. The bandwidth of that filter (and to some extent it’s temperature dependance) place
> a “best case” limit on performance in the 10’s to 100’s of ms range depending on the 
> exact details. There are higher performance receivers (but not a lot of them) that do get into
> the single digit ms range. At that point the propagation issue mentioned above needs some
> work. 
> 
> Further complicating things is the distance factor. A user in Denver with ground wave “view” 
> of the transmitter will do *much* better than the numbers above. A user in Miami or Bangor ME 
> may be very lucky to get close to the numbers above on an intermittent basis. 

I'm basically familiar with the ground wave / sky wave problem. Quite
some time ago I had found a PDF on the 'net with some explanations,
measurements, and a U.S. map showing e.g. which regions were mostly
affected by temporary cancellation due to interference of the sky and
groundwave with the same amplitude.

If I remember correctly this was an old publication from NIST or so.
Eventually it's hard to find by search machines since it wasn't a
generated PDF with text, but just a scan of an old printed article.

Unfortunately I hadn't saved a copy, and now I'm unable to find it.
Anybody has a hint what this could have been?


Thanks,

Martin