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*Subject*: R: [amsat-bb] Re: Asteroid echos on 2380 MHz*From*: "i8cvs" <domenico.i8cvs@xxxxxx>*Date*: Sat, 17 Aug 2002 04:54:15 +0200

Hi Dan N8FGV, The attenuation of a signal sent to the asteroid and reflected back to the earth,lets call it EAE Earth-Asteroid-Earth must be computed using the RADAR equation as normally we do for an EME signal. Distance Earth-Asteroid = 527000 Km = 527000000 meters Diameter of Asteroid= 500 meters Reflectivity coefficient of the Asteroid :we estimate 7% of the incident RF power as for the surface of the moon but it can be more than 7% depending on the material by wich the Asteroid is composite but we don't know this data. The asteroid as seen as a RADAR target is a disk with a radius of 250 meters wich surface Sa is: 2 Sa = 250 x 3.14 = 196350 square meters Suppose now that we are located at the center of a sphere wich radius is the distance from the earth to the asteroid or R=527000 Km and suppose that we radiate all around the power P = 1 W using an isotropic antenna for 2380 MHz The surface S of the above sphere can be computed with: 2 S= 4 x 3.14 x R and 6 2 18 S = 4 x 3.14 x ( 527 x 10 ) = 3.49 x 10 square meters Transmitting isotropically 1 W from the center of the sphere the power density D received on every square meter of the above sphere is 1 - 19 D=-------------------- = 2.86 x 10 W / square meter 18 3.49 x 10 The power density P1 collected by the asteroid surface as transmitted by the earth using an isotropic antenna with the power of 1 W is than given by D x Sa - 19 -14 P1= 2.86 x 10 x 196350 = 5.62 x 10 watt The reflectivity capability of the asteroid is 7% of the above power and so the isotropic radiated power echo P2 from the asteroid is: -15 P2= 3.9 x 10 watt The above P2 power is now reflected back "isotropically" all around by the asteroid and is totally collected again by the surface S of the sphere and so the power density P3 collected on every square meter on the earth surface is P2/S or: -15 3.9 x 10 -33 P3= ----------------- = 1.12 x 10 W/square meter 18 3.49 x 10 Now it is necessary to know how much of the P3 power is collected by an isotropic antenna for 2380 MHz on the earth. The aperture area A of an isotropic antenna can be computed using the following formula: 2 A= lambda / 4 x 3.14 and for 2380 MHz A= 0.00126 square meters The power Pr received by the isotropic antenna and available on its connector is than P3 x A or -33 -36 Pr = 1.12 x 10 x 0.00126 = 1.41 x 10 watt The isotropic path attenuation Earth-Asteroid-Earth is than computed dividing the power P=1 W isotropically radiated from the earth by the power Pr received back from the asteroid on the earth using the same isotropic antenna. 1 Isotropic attenuation = 10 log ------------------ = 358,5 dB 10 -36 1.41 x 10 Following the ARRL Newington CT,informations on day 15, 2002 the Arecibo Radiotelescope will transmit as well CW using a power of 900 Kw to its 73 dBi gain antenna so that having already computed the EAE attenuation of 358,5 dB at 2380 MHz we can now compute the signal to noise ratio S/N at Arecibo considering that their receiver equivalent noise temperature is 4 K and the cold sky is 3 K and that they receive on CW with a band width of 500 Hz as normally we do on EME Under this conditions the Arecibo receiver noise floor Pn with the antenna connected is: -23 -20 Pn = 1.38 x 10 x ( 4 + 3 ) x 500 = 4.83 x 10 watt = - 193.16 dBW = - 163 .16 dBm Arecibo power = 900 KW = ..................+ 59.54 dBW Arecibo antenna gain =..........................+ 73.00 dBi -------- Arecibo EIRP............................................+132.54 dBW Isotropic attenuation AEA.................... - 358.5 0 dB --------- Power received at earth on isotropic antenna ......................................................- 225.96 dBW Arecibo antenna gain............................... + 73 .00 dBi --------- Available power at Arecibo antenna - 152.96 dBW Arecibo receiver noise floor on CW - 193.16 dBW --------- - Arecibo (S+N)/N ratio on CW...............+ 40.20 dB CONCLUSION: The antenna gain at Arecibo is 73 dBi and a (S+N)/N ratio of 40.2 dB is received. In order to receive the same signal but with a (S+N)/N = 0 dB is necessary to use an antenna with a gain of 73- 40.2 = 32.8 dBi In addition no Radio Ham has a receiver with a noise temperature of 4 K so that assuming to use a state of the art preamplifier with NF= 0,35 dB the receiver noise floor under the same condition rises to -186,65 dBW so that and antenna extra gain of -186,65 -(-193,16) = 6,51 dB is necessary. The total necessary antenna gain is than 32,8 + 6,51 = 39.31 dBi At 2380 MHz a dish of minimum 5,5 meter in diameter is necessary to achive such gain but many amateur EME users are using even biger dishes so that the experiment seams to be succesfully possible. In addition using software type that of AF9Y is possible to detect CW signals almost 30 dB belove the noise. In addition many EME operators are trained to receive CW signal well down the noise by ears I hope this help a bit 73" de i8CVS Domenico ----- Original Message ----- From: Dan Schultz <n8fgv@AMSAT.Org> To: <amsat-bb@AMSAT.Org> Sent: Friday, August 16, 2002 11:39 PM Subject: [amsat-bb] Re: Asteroid echos on 2380 MHz > A good source of information on the asteroid flyby is > http://skyandtelescope.com. The site includes finder charts. > > Sky and Telescope reports the diameter as 500 meters (1/3 mile) and a > flyby distance of 527,000 kilometers (327,000 miles). Given that the > moon is 3475 kilometers (2159 miles) diameter at an average distance of > 384,000 kilometers (239,000 miles), we can calculate as follows: > > Size difference: > (500 meters) ^ 2 / (3475 km) ^ 2 = 48,302,500 times smaller projected > area than the moon > 10*LOG (48,302,500) = 76.8 dB worse. > > Range difference: > (527,000 kilometers) ^ 4 / (384,000 kilometers) ^ 4 = 3.55 times less > signal > 10*LOG(3.5) = 5.5 dB worse. > > Total: 82.3 dB worse. > > Using your figures for Arecibo uplink power and antenna gain, the 80 dB > gain will just about offset the 82.3 dB loss due to the smaller size and > greater distance of the asteroid. It should be only 2.3 dB worse than a > 100 watt amateur EME station. However I think most EME stations run more > than 100 watts, the asteroid reflection would be 12.3 dB worse than an > amateur EME station running 1 KW. So let's give it a listen and see if > you can hear it. > > Dan Schultz N8FGV > > > >The asteroid is purportedly about 1/2 mile in diameter and passing at a > > >distance of 300,000 miles (just beyond the orbit of the moon). So how > >strong an echo will this tiny rock produce compared to a moonbounce > signal > >(off a much bigger rock!)? Of course Arecibo will be running a signal > 9000 > >times as powerful as is used on 2304 MHz eme (avg 100w), and with 40 dB > > >more antenna gain! That's about 80 dB stronger! the moon is about a > >quarter the size of the earth (guessing 2000 miles diameter) so that is > > >(very) roughly (Drock)^2/ (Dmoon)^2 = 1/16,000,000 weaker reflection! > > >So whatdya say? Is this possible? > > >Ed, AL7EB > > ---- > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org ---- Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

**References**:**Re: Asteroid echos on 2380 MHz***From:*Dan Schultz

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