Not surprisingly the first pulsar parameter that should be considered is the strength of the pulsar radio signal. The signal strength is expressed as a flux density and has units of a jansky - named after Karl Guthe Jansky, an American radio engineer who first discovered radio waves emanating from the Milky Way.
The jansky (symbol Jy) is a non-SI unit of spectral flux density equivalent to 10−26 watts per square metre per hertz.
As a yardstick, collecting the energy from a 1 Jy source with the currently largest known antenna (FAST: 500 m in diameter) and over a bandwidth of 1 GHz (FAST: maximum current bandwidth) would return just 2 x 10−12 watts (assuming 100 % illumination of the aperture with 100 % efficiency). It would be necessary to accumulate the energy thus received for about 16,000 years to power a 1 W light bulb for just 1 second !!!
Using typical amateur equipment values (10 m diameter dish @ 70 % efficiency) and, say, 10 MHz bandwidth, the received energy becomes about 6 x 10−18 watts and it would take about 5,000 million years to accumulate enough energy to power a 1 W light bulb for one second !!!
Another measure is that it would take (in the 500 m antenna case) 16 years to accumulate enough energy to fly a bee for 1 second and, similarly, for the amateur case (10 m antenna) it would take 5 million years.
Only the Vela pulsar exceeds 1 Jy by any significant amount (5 Jy @ 400 MHz).
The challenges of detecting pulsars are clearly shown by the tables here which list the relative flux densities (in descending order) of a number of pulsars. It can be seen that after the first two pulsars (B0833-45, B0329+54) the signal strength drops away rapidly. As a result the usual candidate for first attempts is B0833-45 (Vela Pulsar) for Southern Hemisphere observers, and B0329+54 for Northern Hemisphere observers. Ironically, the first pulsar discovered (by Jocelyn Bell in 1967), B1919+21, would be too weak at 400 MHz and 1400 MHz for the usual amateur setup as shown by this extract from the ATNF Pulsar Catalogue.
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# NAME PSRJ RAJ DECJ P0 DM W50 W10 S400 S1400
(hms) (dms) (s) (cm^-3 pc) (ms) (ms) (mJy) (mJy)
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1 B1919+21 J1921+2153 19:21:44.8 +21:53:02.2 1.337302 12.44 30.900 40.800 57.00 6.00
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At 400 MHz the 57 mJy signal strength of B1919+21 places it at #72 position in a list ordered by pulsar signal strength. At 1400 MHz the signal strength of 6 mJy places it at #89. The B1919+21 is nearly 88 times weaker at 400 MHz, and 183 times weaker at 1400 MHz than the strongest pulsar (B0833-45 - Vela). So, ironically, it is unlikely that the 'original' pulsar would be detected by amateurs unless the dish size is larger than about 15 metre - 20 metre in diameter; but advances are made all the time and so this requirement might be reduced.
It may seem odd that B1919+21 was the first pulsar discovered when it is well down in the list of signal strength. A number of factors might explain this. Firstly, nobody was looking for pulsars at that time (even though theoretically predicted years before) and the equipment had slow response times specifically to average out terrestrial noise for the usual observations. The facility at Cambridge which Jocelyn Bell operated was unusual for the time as it was looking for interplanetary scintillation (effect on radio waves from cosmic sources caused by the solar wind) which required a fast response time - a characteristic necessary to see a pulse. Also working in favour of the detection was the low frequency of observation (where signals are stronger) of 81.5 MHz and a very large antenna (about 4 acres of dipoles !). Serendipitously the dispersion measure for B1919+21 is low at 12.44, meaning that a wide bandwidth could be used without smearing the pulse.
As an introduction, in the above ATNF Pulsar Catalogue extract for B1919+21, we have, in left to right order...
Name - original designation made from RA and DEC - which sometimes are inaccurate (e.g. Vela - B0833-45)
PSRJ - more modern designation also made from RA and DEC - usually more accurate (e.g. Vela - J0835-4510)
RAJ - Right Ascension
DECJ - Declination
P0 - period of pulse (seconds)
DM - dispersion measure
W50 - width of the pulse measured between 50% power points of the pulse (ms)
W10 - width of the pulse measured between 10% power points of the pulse
S400 - flux density at 400 MHz in mJy
S1400 - flux density at 1400 MHz in mJy
There are over 2500 pulsars listed in the ATNF Pulsar Catalogue, but only a fraction of that number are in reach of the average amateur. However, armed with good knowledge of their target and a 25 metre dish the Astropeiler Group have managed to detect over 90 pulsars @ 1296 MHz - at least two of them binary pulsars.
Even so, the activities of the amateur radio astronomer is realistically restricted to detecting known pulsars - but of course, one can dream...