[time-nuts] Result of Earth Quake speeds up earth?
jimlux at earthlink.net
Sun Mar 20 18:15:26 UTC 2011
On 3/19/11 10:41 PM, Bruce Griffiths wrote:
> Bruce Griffiths wrote:
>> jimlux wrote:
>>>> A 10-12m diameter dish is probably close to the minimum feasible
>>>> A 4m dish can be made to work in conjunction with a mauch larger dish
>>>> (eg 30m).
>>> The original speculation was for measuring the small change in earth
>>> rotation rate, for which some sort of interferometric measurement of
>>> a stellar source could be used.
>>> The source has to be bright (so you can detect it with a practical
>>> antenna.. not everyone has a 30m dish in their back yard)
>>> The source has to be small angle (or at least something that you
>>> could accurately determine the centroid of)
>>> The source has to be "not moving" (which I think leaves out using
>>> something like jupiter)
>>> The frequency of measurement has to be somewhere that the atmosphere
>>> won't dominate the uncertainty (leaving out optical, I think)
>>> SO what's the brightest small angular radio source out there?
>> RA 12:29.1 DEC 02:03.1
> Its flux density is around 30 Jy in the waterhole region.
> ie about 3E-17W per square meter for a 100MHz bandwidth.
> The radio spectrum is relatively flat due to the synchroton nature of
> the blazar source.
Ok, so lets say our ambitious amateur has a 3 meter diameter dish..
that's about 7 square meters. Knock that down to 4 square meters to
make up for illumination and feed issues. So we're looking at 12E-17 W
or 1.2E-13 mW or -130dBm, in 100 MHz BW.
Say we want the "signal" to be comparable to the noise power, what do we
need for a noise temperature.. kTB = -130dBm. kT = -174dBm/Hz for 300K,
B = 80dBHz. (so at room temp, kTB would be -94dBm.. we need to drop
noise power by at least 40 dB, so T needs to be down in the "sub 1 K"
area, which is totally impractical.
Looks like we need a bigger antenna..
Unless there's some clever correlation scheme.
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