[time-nuts] Pulsars (was: 60 KHz Receiver)
jim...@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. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Pulsars (was: 60 KHz Receiver)
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:hmur...@megapathdsl.net] Sent: 05 October 2010 07:30 To: Discussion of precise time and frequency measurement Subject: [time-nuts] Pulsars (was: 60 KHz Receiver) jim...@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. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. This email, including any attachment, is a confidential communication intended solely for the use of the individual or entity to whom it is addressed. It contains information which is private and may be proprietary or covered by legal professional privilege. If you have received this email in error, please notify the sender upon receipt, and immediately delete it from your system. Anything contained in this email that is not connected with the businesses of this company is neither endorsed by nor is the liability of this company. Whilst we have taken reasonable precautions to ensure that any attachment to this email has been swept for viruses, we cannot accept liability for any damage sustained as a result of software viruses, and would advise that you carry out your own virus checks before opening any attachment. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Pulsars (was: 60 KHz Receiver)
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.ree...@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:hmur...@megapathdsl.net] Sent: 05 October 2010 07:30 To: Discussion of precise time and frequency measurement Subject: [time-nuts] Pulsars (was: 60 KHz Receiver) jim...@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. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. This email, including any attachment, is a confidential communication intended solely for the use of the individual or entity to whom it is addressed. It contains information which is private and may be proprietary or covered by legal professional privilege. If you have received this email in error, please notify the sender upon receipt, and immediately delete it from your system. Anything contained in this email that is not connected with the businesses of this company is neither endorsed by nor is the liability of this company. Whilst we have taken reasonable precautions to ensure that any attachment to this email has been swept for viruses, we cannot accept liability for any damage sustained as a result of software viruses, and would advise that you carry out your own virus checks before opening any attachment
