[time-nuts] Fundamental limits on performance

Lux, Jim (337C) james.p.lux at jpl.nasa.gov
Sun Sep 13 17:44:17 UTC 2009

On 9/13/09 10:03 AM, "Hal Murray" <hmurray at megapathdsl.net> wrote:

> bruce.griffiths at xtra.co.nz said:
>> Adding a 210ft diameter antenna to the spacecraft just to detect a
>> sufficient number of pulsars is probably not an option.
>> Unless a multibeam phased array is used simultaneous observation of
>> several pulsars isnt possible.
> What sort of frequencies do people use to listen to pulsars?
> Do I need 210 ft for collecting area or pointing accuracy?  Would a big
> phased array be useful and lighter?

Phased arrays raise their own issues.. If you use passive feed networks, you
have to worry about their losses.  If you have LNAs on each element (or
subarray), then you have matching issues.  However, phased arrays for space
applications probably are the future.

(they also use DSN 34m antennas for pulsar detection.. That's only a bit
more than 100ft.  DSN uses pulsars for Delta DOR time reference.. A sort of
VLBI to determine the cross range/azimuth of the spacecraft.. Point to
pulsar, point to s/c, point to pulsar, point to s/c, recording all the

> Does anybody on Earth used phased arrays to listen to several pulsars
> simultaneously?
>> Kolmolgorov turbulence in the interstellar medium can cause all but
>> the singals from the most distant pulsars to fade randomly.
> Ugh.  Now I have to figure out what that means.  It looks interesting, but my
> head hurts already.  Is there an analogy in the electrical world?

Twinkling of stars?

> --
> These are my opinions, not necessarily my employer's.  I hate spam.
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