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

[jimlux]

On 8/5/20 4:18 PM, Mark Haun wrote:
> 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.

yes, there is a directory of ionosondes.. I can't lay my fingers on it 
right now, but it's there.

> 
> 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?
> 

I don't know how much VLF is used these days, but I'm sure their timing 
is derived from a GPSDO if nothing else.


Very little propagates to space, ionospheric absorption blocks VLF for 
the most part.
And, as we head into the next solar cycle, ol' Sol is cranking up, so 
the "thou shall not pass" frequency is rising.

https://solar-radio.gsfc.nasa.gov/wind/burst_images/wind_stereo_20130522.png

is a picture of the spectrum for a 24 hour period recorded in 3 places, 
when there was a big Type II burst (associated with Coronal Mass 
Ejections) (and a few type III bursts, which are more common,and a lot 
faster)

It's not the best to see the diurnal variation in propagation, but look 
at the top part of the plots above 1 MHz.


> 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.
> 
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