Antenna for receiving pulsar signals

Given a quiet local environment and several hours of
integration time, what rough size of antenna would be
needed to receive millisecond pulsar signals?

George

On a sunny day (Thu, 15 Jan 2004 19:57:06 -0000) it happened "George Dishman"
wrote in :

Given a quiet local environment and several hours of
integration time, what rough size of antenna would be
needed to receive millisecond pulsar signals?

George
Not sure what you mean, but if the 'integration time' is longer
then milliseconds, you for sure will not be able to detect those milliseconds
(as modulation in amplitude).
You will detect there is something there (average power).
So you mean measurement time?
No idea, depends on how strong the signal is, and I dunno that.

"Jan Panteltje" wrote in message
...
On a sunny day (Thu, 15 Jan 2004 19:57:06 -0000) it happened "George
Dishman"
wrote in
:

Given a quiet local environment and several hours of
integration time, what rough size of antenna would be
needed to receive millisecond pulsar signals?

George
Not sure what you mean, but if the 'integration time' is longer
then milliseconds, you for sure will not be able to detect those
milliseconds
(as modulation in amplitude).
You will detect there is something there (average power).
So you mean measurement time?
No idea, depends on how strong the signal is, and I dunno that.

If you already know the period of the pulsar it is possible to integrate the
signal and raise it above the noise background. Probably would employ
an electronic device known as a phase-locked loop, which can "lock-on"
to a weak signal if it is set close to the signal frequency ( the weaker the
signal, the closer the PLL has to be set to the exact signal frequency ).

Andy

In message , George Dishman
writes
Given a quiet local environment and several hours of
integration time, what rough size of antenna would be
needed to receive millisecond pulsar signals?

An acre or two of phased array dipoles should be enough to get started.
Though you may need more than that to get down to the millisecond
pulsars even with sophisticated integration techniques.

ISTR about 20000m^2 of aerial discovered the Crab nebula at ~80MHz

Regards,
--
Martin Brown

In message , George Dishman
writes
Given a quiet local environment and several hours of
integration time, what rough size of antenna would be
needed to receive millisecond pulsar signals?

You may want to contact the Society of Amateur Radio Astronomers:

http://www.qsl.net/SARA/

They've had a recent thread about just this.

Quiet skies,

tom

--
We have discovered a therapy ( NOT a cure )
for the common cold. Play tuba for an hour.

On a sunny day (Fri, 16 Jan 2004 00:37:24 -0000) it happened "andrewpreece"
wrote in :


"Jan Panteltje" wrote in message
...
On a sunny day (Thu, 15 Jan 2004 19:57:06 -0000) it happened "George
Dishman"
wrote in
:

Given a quiet local environment and several hours of
integration time, what rough size of antenna would be
needed to receive millisecond pulsar signals?

George
Not sure what you mean, but if the 'integration time' is longer
then milliseconds, you for sure will not be able to detect those
milliseconds
(as modulation in amplitude).
You will detect there is something there (average power).
So you mean measurement time?
No idea, depends on how strong the signal is, and I dunno that.

If you already know the period of the pulsar it is possible to integrate the
signal and raise it above the noise background. Probably would employ
an electronic device known as a phase-locked loop, which can "lock-on"
to a weak signal if it is set close to the signal frequency ( the weaker the
signal, the closer the PLL has to be set to the exact signal frequency ).

Andy
Yes that is one method, to try to lock a PLL to it,
however PLL does not like noise at all.
So then your loop filter for the PLL will have to have a low bandwidth.
Normally, the way I see it, if a signal (noise with some of the pulsar
pulsing in it at frequency x), you would take n samples (so for a fixed
sample frequency a specific time), run a FFT on it.
In the resulting frequency spectrum you would see a peak at say 1 kHz
(if the pulsar pulsed once every millisecond).
The more samples you have (the longer your data, *receiving time*), the
better the result of the fft.
You need at least a (Nyquist) 2 x the pulsar frequency to make anything
out.
So integration is (in this example) not the right word.
This is the way *I* would look for a signal (more advanced algos exist).
When using a non digital setup, you are heterodyning , down mixing from some
short wavelength, and then use a AM detector, it would show a 1 ms pulsar as
a 1 kHz beep (on a speaker), slower ones do 'phhs', 'phhs', 'phhs',
with each 'phhs' for one revolution of the pulsar (not sure if it pulses
twice or once per revolution, may depend on the angle dunno).
It is a typical sound, I have heard it.
And noise...
The filter after the AM detector is a lowpass (you can call that an
integrator), and it must be able to pas the 1000 Hz as in this example, a
1 Hz low pass would give you no pulsar 'sound'.
It WOULD give some DC level that you could detect.
As good narrow band filter (once you find the frequency) (parametric equalizer
for example) could filter out more noise and you'd have a nice reference that
you could then sync you watch to..
Pulsar is supposed to be very stable....
Note no PLL here, but could be used of cause.
This is all I know about pulsars, but the electronics I can expand on if you
wish.
JP

"Jan Panteltje" wrote in message
...

You might also wish to look at software methods to pull
the signal out of the collected signal. See, for
example, Scargle Periodogram methods.

I did an article on this for The Orrery newsletter a while
back.


--
-----------------------------------------------------------------------
Greg Neill, Editor
The Orrery: Models of Astronomical Systems
http://members.allstream.net/~gneill/
-----------------------------------------------------------------------

On a sunny day (Fri, 16 Jan 2004 13:02:49 -0500) it happened "Greg Neill"
wrote in
:

"Jan Panteltje" wrote in message
...

You might also wish to look at software methods to pull
the signal out of the collected signal. See, for
example, Scargle Periodogram methods.

I did an article on this for The Orrery newsletter a while
back.


I just did a Google for Scargle Periodogram pulsar.
Very interesting, finding planets around pulsars with it.
Even with missing data points.
http://astrosun.tn.cornell.edu/~akgun/Grad/pulsarz.ps
Nice paper too.
Thank you.

--
-----------------------------------------------------------------------
Greg Neill, Editor
The Orrery: Models of Astronomical Systems
http://members.allstream.net/~gneill/
-----------------------------------------------------------------------

Martin Brown wrote:
In message , George Dishman
writes

Given a quiet local environment and several hours of
integration time, what rough size of antenna would be
needed to receive millisecond pulsar signals?


An acre or two of phased array dipoles should be enough to get started.
Though you may need more than that to get down to the millisecond
pulsars even with sophisticated integration techniques.

ISTR about 20000m^2 of aerial discovered the Crab nebula at ~80MHz

Regards,

That sounds about right. Francisco Reyes here at UF made many
pulsar observations with our 26 MHz array (16000m^2) and his 46 MHz
array in Chile (10000m^2). You will need to work at a higher
frequency to get millisec pulsars because of dispersion.
--
John Oliver
Associate Professor
Associate Chair/Undergraduate Coordinator
Department of Astronomy
University of Florida
Project AST@RHO http://astrho.astro.ufl.edu
see the night sky at http://concam.net/rh/

First I'd like to thank all who have replied, the information
provided has been very helpful.

"Jan Panteltje" wrote in message
...
On a sunny day (Fri, 16 Jan 2004 00:37:24 -0000) it happened
"andrewpreece"
wrote in :


"Jan Panteltje" wrote in message
...
On a sunny day (Thu, 15 Jan 2004 19:57:06 -0000) it happened "George
Dishman"
wrote in
:

Given a quiet local environment and several hours of
integration time, what rough size of antenna would be
needed to receive millisecond pulsar signals?

George
Not sure what you mean, but if the 'integration time' is longer
then milliseconds, you for sure will not be able to detect those
milliseconds (as modulation in amplitude).
You will detect there is something there (average power).
So you mean measurement time?
No idea, depends on how strong the signal is, and I dunno that.

If you already know the period of the pulsar it is possible to integrate
the
signal and raise it above the noise background. Probably would employ
an electronic device known as a phase-locked loop, which can "lock-on"
to a weak signal if it is set close to the signal frequency ( the weaker
the
signal, the closer the PLL has to be set to the exact signal frequency ).

The weaker the signal, the narrower the bandwidth of the
loop filter needed to reject the noise to below the signal,
and of course the initial PLL frequency has to be within
about a bandwidth of the actual signal.

However, AIUI, pulsar signals are broadband. As a result I
had assumed the signal would also be non-coherent (i.e. not
a modulated sine wave but amplitude modulated noise) but a
page on "Phase-coherent De-dispersion" has made me wonder
about that now.

Dispersion arises because different frequencies are delayed
by different amount by the interstellar medium (ISM) so if
you had a wide enough bandwidth on the receiver, it could
be delayed a whole cycle and the sum would be a continuous
constant level.

http://www.jb.man.ac.uk/~pulsar/Educ...00000000000000

Yes that is one method, to try to lock a PLL to it,
however PLL does not like noise at all.
So then your loop filter for the PLL will have to have a low bandwidth.
Normally, the way I see it, if a signal (noise with some of the pulsar
pulsing in it at frequency x), you would take n samples (so for a fixed
sample frequency a specific time), run a FFT on it.
In the resulting frequency spectrum you would see a peak at say 1 kHz
(if the pulsar pulsed once every millisecond).
The more samples you have (the longer your data, *receiving time*), the
better the result of the fft.
You need at least a (Nyquist) 2 x the pulsar frequency to make anything
out.

Imagine a simple wideband receiever with a fast amplitude
detector on the output. The 'signal level' would vary on
sub-millisecond timescales. Put that amplitude rather than
the RF signal itself into the FFT and you would get what you
describe. Note the "Square law detectors" in this:

http://tucanae.bo.astro.it/pulsar/32mt/

The use of the term "Phase-coherent" when talking of de-
dispersion puzzles me since RF phase information is discarded
by such a detector.

So integration is (in this example) not the right word.

The key is what Andy said, "If you already know the period
of the pulsar ..."

Suppose the period is known to be exactly 1ms. By sampling
the RF amplitude every 100us and adding the value to a set
of ten 'bins', the pulse shape emerges from the noise:

http://www.radiosky.com/rspplsr.html

The trick is that the free-running clock doing the 100us
timing has to stay exactly in step with the unknown signal
for the integration period or the pulse will just smears
over the bins and give the average in all. This is where
I was wondering if timing the sampling with an atomic clock
could allow longer integration periods and hence a smaller
antenna.

This is the way *I* would look for a signal (more advanced algos exist).
When using a non digital setup, you are heterodyning , down mixing from
some
short wavelength, and then use a AM detector, it would show a 1 ms pulsar
as
a 1 kHz beep (on a speaker), slower ones do 'phhs', 'phhs', 'phhs',
with each 'phhs' for one revolution of the pulsar (not sure if it pulses
twice or once per revolution, may depend on the angle dunno).
It is a typical sound, I have heard it.
And noise...
The filter after the AM detector is a lowpass (you can call that an
integrator), and it must be able to pas the 1000 Hz as in this example, a
1 Hz low pass would give you no pulsar 'sound'.
It WOULD give some DC level that you could detect.
As good narrow band filter (once you find the frequency) (parametric
equalizer
for example) could filter out more noise and you'd have a nice reference
that
you could then sync you watch to..
Pulsar is supposed to be very stable....

They can be more stable than atomic clocks!

Note no PLL here, but could be used of cause.
This is all I know about pulsars, but the electronics I can expand on if
you
wish.

If you have any information how broadband de-dispersion
might be performed in the RF stage, say by a configurable
flat gain frequency-dependent phase shifter, I would be
very interested.

George