[amsat-bb] Re: HF Satellite Relay
i8cvs
domenico.i8cvs at tin.it
Wed Jun 30 15:11:27 PDT 2010
----- Original Message -----
From: "Tony" <dxdx at optonline.net>
To: "AMSAT-BB" <amsat-bb at amsat.org>; "i8cvs" <domenico.i8cvs at tin.it>
Sent: Wednesday, June 30, 2010 10:31 AM
Subject: Re: [amsat-bb] Re: HF Satellite Relay
> Dominico,
>
> The 10M sphere brought another question to mind -- Mike Wantanabe,
> JH1KRC, managed to hear his own EME echoes on the 21MHz using a KW and a
> 6 element Yagi. Details and recordings are on his website (see below). I
> was wondering how the path loss calculations compare with his EME results.
>
> http://eme.dokidoki.ne.jp/sound/jh1krc/index.html
>
> Thanks Dominico...
>
> Tony -K2MO
>
Hi Tony, K2MO
I have heard the EME echoes on the 21 MHz EME test from JH1KRC and they
are very strong for a 6 element yagi claiming 18 dBi at 10° elevation and 1
KW output at the antenna but the moon was only 10.8° above the horizon for
JH1KRC so that he was advantaged by the gain of the ground at such low moon
elevation.
By the way on day 14 jan 2006 the moon was at a distance of 400.000 km from
the earth and at a range of 405.000 km from JH1KRC so that the elapsed time
from TXing to the echoes must be ( 405.000 x 2 ) / 300.000 = 2.7 seconds and
this by hears seems to be accordingly.
We know that the range from the Moon and JH1KRC was 405.000 km and we
know that the radius of the Moon is 1735 km or 1735 x 10^3 meters
Also we know that the reflectivity coefficient of the moon at 21 MHz is 7 %
The 21 MHz Round Trip Isotropic Attenuation using the concept of Radar
Equation is as follows:
Pt x Gt x Ar x Sigma
Pr = ------------------------------
(4 x 3.14 x R^2)^2
where :
Pr = received power
Pt = transmitted power = 1watt
Gt = gain of a 21 MHz isotropic antenna = 1 in power ratio
Ar = Aperture of the isotropic antenna at 21 MHz in square meters.
R = Radius of a sphere wich distance from the earth is 405 x 10^6
meters i.e the distance from the Moon and the earth expressed
in meters.
Sigma = Surface of the Moon in square meters i.e. of the Moon as a
radar target like a disc multiplied by the reflectivity
coefficient of 7 %
Computing:
/ 2 2
/\ 14.3
Ar = ---------- = ----------- = 16.24 square meters
4 x 3,14 4 x 3,14
Sigma = (1735 x 10^3) ^2 x 3.14 x 0.07 = 6.62 x 10^11 square meters
1 x 1 x 16.24 x (6.62 x 10^11)
Pr = --------------------------------------- = 2.53 x 10^-24 watt
[(4 x 3.14 x ( 405 x 10^6)^2]^2
1
Round trip attenuation = 10 log ----------------- = 236 dB
2.53 x 10^-24
Assuming that we are using a good HF receiver with a NF= 8 dB
equivalent to 1539 kelvin we must consider in addition that the receiver
sensitivity is limited by the external available noise power.For quiet,rural
locations as that of JH1KRC the galactic noise is the limiting factor and
at 21 MHz the noise temperature is around 29.000 kelvin so that reducing
the Noise Figure belove 8 dB at 21 MHz do not improve the S/N ratio.
In addition during the 15mEME01 QRO test on CW JH1KRC claims to
have used a RX CW filter with a bandwidth of only 10 Hz as you can
read in his web page.
http://eme.dokidoki.ne.jp/sound/jh1krc/index.html
With the above data the noise floor of this receiver for CW into a
bandwidth of 10 Hz can be calculated as follows:
Noise Floor = KTB = 1.38 x 10^-23 ( 1539 + 29.000 ) x 10 = - 173.7 dBW
or - 142.6 dBm
Link budged calculation:
TX power 1000 watt.............................+30 dBW
TX Antenna gain....................................+18 dBi
-----------
Transmitted EIRP .................................+48 dBW
Round trip attenuation 1500 km..........- 236 dB
-----------
Received power Pr on isotropic
antenna on the earth ..............................-188 dBW
RX antenna gain....................................+ 18 dB
-----------
Available power at RX input............... - 170 dBW
RX noise floor...................................... - 173.7 dBW
-----------
Signal received with a S/N ratio.......... + 3.7 dB
So according with the above calculations the signal of JH1KRC is 3.7 dB
over the noise and so it is detectable very strong as recorded in the file
15m01142006_31qro in the following web page.
http://eme.dokidoki.ne.jp/sound/jh1krc/index.html
In addition since the test was made with the Moon at a very low elevation
of 10.8° we must add to 3.7 dB at least 1 or 2 dB or more due to the gain
of the ground.
Probably if a new test will be made at higher moon elevation the echoes
of file 15m01142006_31qro would be audible but not so spectacular.
Best 73" de
i8CVS Domenico
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