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Report on new optimized Astropulse apps for Windows
Raistmer:
--- Quote from: Jason G on 22 Nov 2008, 10:23:29 am ---NoNo, not Pulse I think... sample... Big difference... Correct me if I am wrong please.
--- End quote ---
Don't know what "sample" is then.
Sample can be (0,0), (0,1), (1,0), (1,1). How it can be more than 12 ?
Probably it's power[] sample, so - pulse.
But sure need to check with actual code...
Jason G:
Right, polarised signal already decoded, complex signal partially blanked.
Comparison:
- A single sample amplitude variation = AM radio (benefit = simple, Disadvantage = short range, noisy )
- peak moving in frequency per time interval = FM radio (benefit = longer range, disadvantage = complex decoding)
- broadband pulses = primitive marconi/morse code telegraph style( very high efficiency/ low power because part of signal can be enough to sufficiently detect, because other interferece will only mask a small part. Long Range. Highly illegal now, because they saturate all neighbouring frequencies. (this would mess up things like telescopes and police radio ;D) [Square wave shape at source]
So broadband pulse is not one high sample:
- Fundamental frequency + harmonics of the fundamental in constructive interference produce the pulse. [ multiple sine waves]
- shape is determined by bandwidth + power [ impure square wave]
Now shift the signal source out 100 light years [ but stationary] :
- different frequency components are 'dispersed' at different rates, so phase alignment is 'stuffed'
- square wave scattered now looks like noise
- dedispersion reconstitutes square wave through constructive interference generating highest peak.
Now put signal on orbiting planet:
- Doppler effect causes chirp and its reverse as planet approaches and accelerates away.
- could be coming toward us too.
- Now dispersed signal is also chirped, so we need dedisperson and dechirp.... :o... big cpu cycles
A pulse is not a AM signal peak, but a combination of sine wave frequencies added together. What we detect will only ever be approximations, however, we can do this approximation on many more places/times in the sky than anybody before in history. The worst radar removal could do is remove the 'guts' of a pulse, which we would probably detect anyway. My 'feeling' is the abundance of overflows we get for now are either radar blanking artefacts, or genuine interstellar sources.
Jason
Raistmer:
--- Quote from: Jason G on 22 Nov 2008, 12:09:12 pm --- My 'feeling' is the abundance of overflows we get for now are either radar blanking artefacts, or genuine interstellar sources.
Jason
--- End quote ---
Or wrong threshould value ;)
sngle pulse finding algorthm compares power with threshould.
"
if (power[m] > state.thresh[l]) {
"
So, at least this simplest form of pulse is power[] elment. (next round - coadded power[] elements, next - coadded and summarized through different data chunks in FFA).
Jason G:
Don't be too quick, Better too low a threshold than too high ;). I reckon some of these may be early human transmissions bouncing around out there too, Ever heard of the Queen Mary phenomenon ?
Raistmer:
--- Quote from: Jason G on 22 Nov 2008, 12:23:46 pm ---Don't be too quick, Better too low a threshold than too high ;). I reckon some of these may be early human transmissions bouncing around out there too, Ever heard of the Queen Mary phenomenon ?
--- End quote ---
What is queen Mary?
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