[time-nuts] Pulsars (was: 60 KHz Receiver)

[Reeves Paul]

Receiving setup - pretty standard amateur eme/radio astromony  kit, good
antenna, LNA, downconverter. Antenna choice depends on frequency, pulsars
are broadband but generally 300 MHz to as many GHz as you can build an LNA.
Amateur attempts seem to be 406, ~600, ~1400MHz. 3m dish minimum or
equivalent yagi arrays (better at lf end). Bandwidth of a few 10s of KHZ or
more - there are trade-offs due to dispersion, high frequencies travel
faster than the low ones so the pulse form is 'spread' but signal levels are
higher at the lower frequencies. De-dispersion can be done in dsp but
probably not real time unless you have lots of cpu power. Best pulsars for
timing would seem to be be the millisecond ones but these are seriously
faint. For getting the signal out of the noise a gated sampling approach is
used locked to the repetition rate and divided down (so a system can be
theoretically used for any pulsar) and driven from a Rb source or better
(the pros use H-masers). There are lists of these things - try CSIRO in
Australia, they have a good on-line database. The Japanese have looked at
pulsars as a replacement for national standards but not sure of the results.
They are (naturally...) slowing down but should be good for a while yet ;-)

regards,
Paul Reeves       G8GJA


-----Original Message-----
From: Hal Murray [mailto:hmurray at megapathdsl.net]
Sent: 05 October 2010 07:30
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Pulsars (was: 60 KHz Receiver)



jimlux at earthlink.net said:
> If you want something that isn't run by governments,and is a technical
> challenge, how about pulsars?   I'd guess (not having looked into it at
> all) that is would be cheaper to set up a station to receive pulsars  than
> to run a Cs standard. 

What sort of gear does it take to hear a pulsar?

What sort of spectrum are they sending?  What frequencies would I listen to?

What sort of bandwidth would the receiver use?

If I have a setup that can hear Pulsar A, will it also be useful for Pulsar
B 
and C and ...?  Or do I need to listen on widely different frequencies?


One problem with pulsars is that they might go below the horizon for part of

the day.

Is there a convenient one up near the north pole?

I assume that they are weak enough that I need a steerable dish.  Is there a

catalog of pulsars that might be interesting to use for amateur timekeeping?

I assume a strong signal would be the primary consideration.

Any chance of hearing one without a dish?


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




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