jimlux wrote:
On 3/15/11 9:36 PM, Hal Murray wrote:
If I were doing this in my backyard on a budget I'd mount a small
telescope nearly straight up so that a bright star would pass through
the field on several nights. I'd measure the light of the star
through a slit and time the peak of the light each night. I bet I
could get to about a microsecond. I'm wondering what professionals
are doing in this field.
I have references for VLBI, if you want. You probably cannot do optical
accurately enough because of "seeing" effects, at least.
What sort of accuracy can I get with:
1) small/medium telescope in suburban back yard
2) small/medium telescope out in the sticks
3) big telescope in a good location
It's sort of time nutty...
Couldn't you rig up a MLBI (medium, not very) setup between you and
someone else in your area..
Could one detect pulses (or a signal) from some quasar (or "infinite
distance" stellar source) with a reasonable small antenna.
Optical methods typically achieve positioning accuracies of around 10
milliarcsec or so.
Radio methods are about 100x more accurate or around 100 micro arc sec.
To achieve the latter synchronisation between antennae has to be better
than around 5us.
However to get fringes from the spectral region around the waterhole
then relative synchronisation between receivers of a few tens of picosec
is required.
Achieving such synchronisation even for an MLBI system would be
something of a challenge without hydrogen masers or equivalent
performance clocks at each antenna.
With care integration times of around half an hour or so are possible
using a hydrogen maser at one antenna and an SRS FS725 rubidium standard
another antenna.
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Using common view GPS carrier phase observables may be an option as long
as the MLBI system isnt too large.
Bruce
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