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<H1>Can Arecibo be heard on a hand-held yagi ?</H1>
<P><FONT face=Tahoma><STRONG>Domenico I8CVS</STRONG> has made some calculations
to determine how well the Arecibo 432.045 MHz signal would be heard on a hand
held Yagi.</FONT></P>
<P><FONT face=Tahoma>Although the Arecibo group, callsign
<STRONG>KP4AO</STRONG>, say the signal can be heard with a small hand-held Yagi
pointed at the moon, Domenico I8CVS reckons a 15 dBi Yagi is required. It will
be interesting to see what people achieve in practice. </FONT></P>
<P><FONT face=Tahoma>What is the smallest 432 MHz antenna that can produce a
detectable signal from Arecibo? Domenico I8CVS has posted these
calculations on the AMSAT bulletin board:</FONT></P>
<P><FONT face=Tahoma>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:</FONT></P>
<P><FONT face=Tahoma><STRONG>Dish diameter: 1000 foot equivalent to 305
meters<BR>Antenna gain: 60 dBi<BR>Tx power: 400 W<BR>Tx Frequency: 432.045
MHz</STRONG></FONT></P>
<P><FONT face=Tahoma>Since the given <STRONG>ERP is 243,902,443 Million Watts
(</STRONG>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.<BR>The rest of the power 400-243 = 157 watt is lost in the
feed line.</FONT></P>
<P><FONT face=Tahoma>At 432 MHz a dish with a diameter of 305 meters has a -3dB
points main lobe angle equal to:<BR>Theta = Lambda / Diameter = 0.69 / 305 =
0.00227 rad.</FONT></P>
<P><FONT face=Tahoma>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</FONT></P>
<P><FONT face=Tahoma>The surface area S = (3.14 x 865^2) / 4 = 5.88 x 10^11
square meters</FONT></P>
<P><FONT face=Tahoma>All the radiated power of 243 watt by the dish is now
collected over the above S area.</FONT></P>
<P><FONT face=Tahoma>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</FONT></P>
<P><FONT face=Tahoma>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.</FONT></P>
<P><FONT face=Tahoma>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.</FONT></P>
<P><FONT face=Tahoma>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.</FONT></P>
<P><FONT face=Tahoma>My ground antenna has a gain G= 15 dBi and an antenna
picked up noise of 70 kelvin when looking at the cold sky</FONT></P>
<P><FONT face=Tahoma>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</FONT></P>
<P><FONT face=Tahoma><STRONG>Link Budget Calculation</STRONG>:</FONT></P>
<P><FONT face=Tahoma><STRONG>Isotropic power reflected by the moon...+12
dBW<BR>Isotropic attenuation for 380.000 Km.. - 197
dB</STRONG><BR>-------<BR><STRONG>Power received on isotropic earth ant... - 185
dBW<BR>Ground antenna gain...............................+ 15
dBi</STRONG><BR>-------<BR><STRONG>Power applied to ground receiver..........-
170 dBW<BR>Noise floor of ground receiver..............- 174
dBW</STRONG><BR>-------<BR><STRONG>Received Signal to Noise ratio S/N.......+ 4
dB</STRONG></FONT></P>
<P><FONT face=Tahoma>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</FONT></P>
<P><FONT face=Tahoma>Signal to Noise ratio</FONT></P>
<P><FONT face=Tahoma>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</FONT></P>
<P><FONT face=Tahoma>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 which is considered to be optimal for a<BR>comfortable reception in
SSB</FONT></P>
<P><FONT face=Tahoma>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 which
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.</FONT></P>
<P><FONT face=Tahoma><STRONG>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</STRONG>.</FONT></P>
<P><FONT face=Tahoma>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.</FONT></P>
<P><FONT face=Tahoma><STRONG>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</STRONG>.</FONT></P>
<P><FONT face=Tahoma>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.</FONT></P>
<P><FONT face=Tahoma>Have fun</FONT></P>
<P><FONT face=Tahoma>73 de <EM><STRONG>I8CVS Domenico</STRONG></EM></FONT></P>
<P> </P>
<P>Arecibo on 432 MHz Moon Bounce April 16-18<BR><A
href="http://www.southgatearc.org/news/april2010/arecibo_432_moonbounce.htm"
target=_blank>http://www.southgatearc.org/news/april2010/arecibo_432_moonbounce.htm</A><BR></P></BODY></HTML>