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

[Jim Palfreyman]

Hi folks,

Well I'm studying pulsars for my Masters at the moment so here's a few
hints and tips. My weekend toy is a 26m radio dish with H masers for
timing.

For the southern hemisphere the Vela pulsar is your best bet.
J0835-4510. It's about a Jansky at 1440 MHz. With the 26m dish I can
see individual pulses - that and the Crab pulsar are about the only
ones available for single pulses with a 26m dish. The receiver is
cooled to about 20K.

Vela, my main subject, is not the best for timing. It glitches
sometimes and only recently sped up.

J0437-4715 is the brightest millisecond pulsar and is very good for
timing. Too faint for individual pulses for me though.

For software look up dspsr and psrchive. These are open source and
will do all the work for you. Dedispersion is essential. Don't forget
that Vela is highly polarized too.

Hot off the presses from a conference last week is that a group of
millisecond pulsars is starting to look like they may outdo earth
based time standards. I saw some very impressive Allan variance
curves.

Oh and for bragging rights go to jimpalfreyman.com and look at "The
Dish" folder where you can see us playing cricket on the famous 60m
dish at Parkes.

Jim Palfreyman

On Tuesday, October 5, 2010, Reeves Paul <Paul.Reeves at uk.thalesgroup.com> wrote:
>
> 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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