In article , Joseph Fenn writes:

I agree with whoever said WWVH in Hawii is l/c and on same status
as wwv in Colorado, so these "skyscan" clocks should perform as
specified. I found though that my latest one will keep time
right to the second for a period of time, the I have to move it upstairs
where reception is better and leave it there for 24 hours. Once
reset to exact time tick I again put downstairs in the shack and its
good for another momth or so. I fail to see how the clock reader
can discriminate between WWVH (on Kauai) and WWV in Colorado.

The answer on "discrimination" is on the NIST time-frequency pages.
The "tick" from WWV in Colorado is 6 cycles of a 1 KHz sine; the
"tick" from WWVH is 5 cycles of a 1.2 KHz sine.

Scoping a receiver detector output will show that. Looks unusual
when somewhere in between Hawaii and Colorado and propagation
makes both about the same strength. :-)

In the ancient times of prehistory, circa 1955 or so, many TV
broadcast stations did a time-sync of station clocks from the fixed
tone onset from WWV...either there or not there and the periodicity
of the background tone was very predictable. WREX-TV did that
in the midwest when I worked there in 1956. Thought that they
would have done it much fancier ways but that albeit crude way
worked out very well to keep station clocks within a second.
[Time is the income commodity of all commercial broadcast
stations and muy importante]

I'm not familiar with the old Heathkit "Most Accurate Clock" for use
on HF at 5, 10, 15 MHz. Someone else can comment on their
discrimination circuits (if any).

Len Anderson
retired (from regular hours) electronic engineer person