# [amsat-bb] Re: Arecibo on 432 MHz Moon Bounce (some calculations)

Idle-Tyme nss at mwt.net
Sat Apr 10 19:50:29 PDT 2010

```Was this sent out on april 1st?

The Original Rolling Ball Clock
Idle Tyme
Idle-Tyme.com
http://www.idle-tyme.com

On 4/10/2010 9:20 PM, i8cvs wrote:
> Hi All,
>
> The specifications of the Arecibo Observatory Amateur Radio Club
> for the 432 MHz Moon Bounce test on April 16-17 and 18 are as
> follows:
>
> Dish diameter: 1000 foot equivalent to 305 meters
> Antenna gain: 60 dBi
> Tx power: 400 W
> Tx Frequency: 432.045 MHz
>
> Since the given ERP is 243,902,443 Million Watts (see below)
> and since 60 dB is equivalent to 1000000 (one Million) time in
> power it comes out that the power reaching the feed of the dish is:
>
> 243902443 / 1000000 =  243 watt
>
> The rest of the power 400-243 = 157 watt is lost in the feed line.
>
> At 432 MHz a dish with a diameter of 305 meters has a -3dB points
> main lobe angle equal to:
>
> Theta = Lambda / Diameter = 0.69 / 305 = 0.00227 rad.
>
> The above lobe of the dish at an average distance of 380000 km
> light up a small circular surface S over the moon wich diameter is:
>
> D = 380000 x 0.00227 = 865 km
>
> The surface area S = (3.14 x 865^2) / 4 = 5.88 x 10^11 square meters
>
> All the radiated power of 243 watt by the dish is now collected over
> the above S area.
>
> The reflectivity of the moon at 432 MHz is the 7% so that the power
> scattered back isotropically by the moon is ( 243/100 ) x 7 = 17 watt
>
> It is like to say that the power reflected back by the moon is 17 watt
> feeding an isoptropic antenna or 17 watt EIRP or +12 dBW EIRP
> radiated isotropically by the moon.
>
> Since the surface of the moon lighed up by the dish is less then the whole
> surface of the moon the usual calculation procedure for the EME link
> considering the isotropic attenuation earth-moon-earth cannot be used
> here because as seen by the Arecibo dish the diameter of the moon is
> smaller than in reality and is large only 865 km in diameter not 3476 km
> as is large in reality the moon.
>
> With this is mind we must imagine the dish of Arecibo to be an isotropic
> antenna with 17 watt applied to it and transmitting all around isotropically
> from the moon.
>
> My ground antenna has a gain G= 15 dBi and an antenna picked up noise
> of 70 kelvin when looking at the cold sky
>
> My receiving system  at 432 MHz has an overall Noise Figure of 0.7 dB
> equivalent to 50 kelvin so that the noise floor KTB of my receiving system
> in SSB with a bandwidth of 2400 Hz is
>
> KTB=1,38 x 10^-23 x (50 + 70) x 2400=3.97x10^-18 watt= -174 dBW
>
>
> Isotropic power reflected by the moon...+12 dBW
> Isotropic attenuation for 380.000 Km.. - 197 dB
>                                                                       -------
> Power received on isotropic earth ant... - 185 dBW
> Ground antenna gain...............................+  15 dBi
>                                                                       -------
> Power applied to ground receiver..........- 170 dBW
> Noise floor of ground receiver..............-  174 dBW
>                                                                       -------
> Received Signal to Noise ratio S/N.......+ 4 dB
>
> By the way when KP4AO will operate on CW I can switch on the 500 Hz
> filter on my receiver and here I will gain in sensitivity 2400/500 = 4.8
> time and  10 log  4.8 = 6.8 dB so that I gain 4 + 6.8 = 10.8 dB of overall
>                           10
> Signal to Noise ratio
>
> If I can stake two 70 cm antennas with gain 15 dBi each I can gain about
> another 3 dB and I can improve the S/N ratio to 10.8 + 3 = 13.8 dB
>
> If I can stack four 70 cm antennas with gain 15 dBi each I can gain about
> another  3 dB and I can improve the S/N ratio up to 13.8 + 3 = 16.8 dB
> a real very strong signal on CW or 16.8 - 6.8 = 10 dB in SSB Signal to
> Noise ratio wich is considered to be optimal for a comfortable reception
> in SSB
>
> By the way to work EME using a big dish having a lobe  with an aperture
> angle "theta" smaller than the diameter subtended by the moon wich
> is about 0.5 degrees i.e. 0.0087 radiants is useful only for the big dish to
> hear better those stations using smaller dishes but the big dish to be
> received better by the smaller one's "must" use more power and not increase
> the diameter of the dish because as soon as the moon is completely resolved
> the power scattered back isotropically do not increase increasing the
> diameter of the dish.
>
> In conclusion I believe that ground stations with an antenna gain of 15 dBi
> and a receiving system with an overall Noise Figure of about 1 dB can easily
> hear KP4AO on CW and barely in the noise on SSB
>
> Stations with the same receiver overall Noise Figure and antenna gain from
> 18 to 21 dB can hear KP4AO on CW and SSB without problems.
>
> Stations using 100 watt or more and the above antennas ranging from 15 dBi
> to 21 dBi have chance to make QSO with KP4AO on CW
>
> The above calculation shows that it is very difficult to hear KP4AO or be
> heard using a small hand-held yagi pointed at the moon.
>
> Have fun
>
> 73" de
>
> i8CVS Domenico
>
> ----- Original Message -----
> From: "MM"<ka1rrw at yahoo.com>
> To:<amsat-bb at amsat.org>
> Sent: Wednesday, April 07, 2010 3:06 PM
> Subject: [amsat-bb] Arecibo on 432 MHz Moon Bounce
>
>
>
>> Hi all:
>> Here is a EME event you cant miss.
>> Dust off your CW key, its time for Satellite, QRP EME.
>>
>> The 1,000 foot dish has 60 dBi on 432 mc and 400 watts.
>> That comes out to be approximately 243,902,443 Million Watts ERP.
>>
>> enjoy
>>
>> wf1f
>> www.marexgm.org
>>
>> (thanks to KB1MGI for passing on this data)
>>
>>
>> Arecibo on 432 MHz Moon Bounce
>>
>> The Arecibo Observatory Amateur Radio Club will be putting the
>> 1000-foot radio telescope on the air for 432 MHz EME from April 16-18.
>>
>> It can be heard with a small hand-held yagi pointed at the moon
>>
>> The scheduled times of operation are:
>>
>> April 16: 1645 - 1930 UTC
>>
>> April 17: 1740 - 2020 UTC
>>
>> April 18: 1840 - 2125 UTC
>>
>> Callsign: KP4AO
>>
>> Tx Frequency: 432.045 MHz
>>
>> Rx Frequency: 432.050 to 432.060+
>>
>> Tx power: 400 W
>>
>> Antenna gain: 60 dBi
>>
>> System noise temp: 120 K (cold sky)
>>
>> System noise temp: 330 K (when pointed at moon)
>>
>> KP4AO can be heard with a small hand-held yagi pointed at the moon and a
>> good receiver. A 15 dBi antenna and 100 W will be enough to work us on
>> CW.
>>
>> Operators at KP4AO will do their best to work as many stations as
>> possible. Each session will start with a brief announcement and CQ in
>> SSB. SSB QSOs may continue for 30 minutes to an hour, if the QSO rate
>> remains high.
>>
>> The mode will be shifted to CW as soon as it is judged that higher QSO
>> rates would result.
>>
>> We will listen for calls at frequencies 5-15 kHz higher than our own,
>> and even higher if QRM warrants. Callers who s-p-r-e-a-d o-u-t are more
>> likely to be copied.
>>
>> If you've already worked us in any mode, please do not call again --
>> give others a chance.
>>
>> If we call "CQ QRP", we will listen for stations running 100 W or less
>> to a single yagi. Please do not answer such a CQ if you are running more
>> power or have a larger antenna.
>>
>> On April 18, if we reach a condition where most calling stations have
>> been worked, and we judge that operating in the digital mode JT65B would
>> produce a higher QSO rate, we will switch to JT65B.
>>
>> Note that any of these planned operating strategies may be changed as
>> circumstances dictate.
>>
>> We are extremely fortunate to have been granted access to the world's
>> largest radio telescope for this amateur radio good-will event. We look
>> forward to working as many stations as possible in the alloted time!
>>
>> > From QRZ.COM
>>
>> KB1MGI
>>
>> Moon-Net Email reflector
>>
>> http://list- serv.davidv. net/mailman/ ...erv.davidv. net
>>
>> Moon Bounce information
>>
>> http://www.vhfdx. info/eme. html
>>
>> UK Ham makes EME contact with just 25 watts
>>
>> http://www.southgat earc.org/ news/jan. ..me_contact. htm
>>
>> Earth-Moon-Earth with 20 Watts
>>
>> http://www.southgat earc.org/ news/jan. ..h_20_watts. htm
>>
>> WSJT Software for EME
>>
>> http://www.physics. princeton. edu/pulsar/ K1JT/
>>
>>
>>
>> _______________________________________________
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>>
>
>
>
> _______________________________________________
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
>
>
>
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