[time-nuts] another source of time...

[Mark Haun]

I wonder if someone maintains a directory of ionosondes.  Seems like
waste/duplication to have every interested party set up their own,
instead of piggy-backing on what's already out there.  There's also the
pollution factor---one certainly hears them often enough while operating
narrowband on shortwave, and while not particularly intrusive, we don't
need more.

I've always wondered about the military VLF stations like NLK (Seattle,
WA) and NAA (Cutler, ME).  Their FSK modulation may not require extreme
frequency accuracy, but it's so easy, perhaps they do lock to GPS?  Of
course, the data themselves are encrypted so you wouldn't be able to
derive anything except a frequency reference.  The advantage would be
they are substantially more powerful than WWVB.  Does much VLF leak out
into space?

Mark

On 05-Aug-20 3:44 PM, jimlux wrote:
> I was researching potential calibration sources for our orbiting
> receivers (where we need to line up GNSS signals with HF signals) and
> after looking at the usual suspects like WWV, we came across another one.
>
> Ionosondes - they're all over the place, and these days, they're
> fairly accurately timed (how accurately? I don't know.)
>
> Timing wise, since wide band and oblique sounders are popular, they
> must be fairly well controlled, since the transmitter and receiver are
> not co-located.  A traditional vertical sounder drives the transmitter
> and receiver off the same clock, so they don't care so much about what
> time it is.
>
> I think these things are designed so they have resolutions in "meters"
> or "tens of meters" which implies sub microsecond accuracy at worst.