R: [amsat-bb] EME at 2401 MHz

["i8cvs" <domenico.i8cvs@xxxxxx>]

----- Original Message -----
From: Bob Bruninga <bruninga@usna.edu>
To: <amsat-bb@AMSAT.Org>
Sent: Tuesday, October 29, 2002 12:55 AM
Subject: [amsat-bb] EME at 2401 MHz


> EME at 2401?
>
> Im sorry to ask this again, but I lost it the last time.  But with so many
> AO-40 receivers on 2401 MHz, and the fact that we will be re-activating
> our 100 W Amp on our 40' Naval Academy dish this week, I wonder if anyone
> with a 1 m dish would be able to hear us via EME?
>
> This is suicide for me to even be contemplating, becuse we are under such
> a crisis schedule, but it would be nice to know the answer so that if we
> ever do find time, and if it is possible, we might be able to set up an
> experiment.
>
> Since I dont remember the answer from a few years ago the last time I
> asked this, probably the answer was "barely" if at all, thus, I promptly
> just forgot about it....and decided it wasnt worth the trouble.. But this
> time I will store the reply under an "EME" folder and will remember the
> anser..
>
> Bob
>

Bob,

The gain of a 40' dish  (12 meters) at 2401 MHz is 47 dBi assuming 55%
efficiency

The gain of a 1 meter dish at 2401 MHz is 25 dBi assuming 50% efficiency

The EME isotropic attenuation at 2400 MHz is 276 dB with the moon at
an average distance of  384.000 km

If the overall noise figure of a good receiver is NF=0,6 dB and the cold
sky temperature is around 10 kelving including the temperature of the
antenna side lobes than the noise floor of  this very good receiving system
using a filter with a band width of 250 Hz on CW  is  -187 dBW= - 157 dBm

Calculation:

Power  applied at the antenna  = 100 W =.............+  20 dBW

Transmitting antenna gain........................................+ 47 dBi
----------------------------------------------------------------------------

Effective Isotropic Radiated Power (EIRP).. ..........+ 67 dBW

EME isotropic attenuation at 2400 MHz............... - 276 dB
----------------------------------------------------------------------------

Power received on a isotropic 2400 MHz.............. - 209 dBW
antenna on the earth

Receiving antenna gain........................................... +  25 dBi

----------------------------------------------------------------------------

Available power at receiver  input........................... - 184 dBW

Receiving system noise floor................................... - 187 dBW
----------------------------------------------------------------------------

(S+N)/N ratio at the receiver output........................  + 3 dB


S/N = ((S+N)/N) - 1  and so a ratio (S+N)/N= 3 dB is equivalent to a  S/N
ratio of 0 dB or signal equal to noise.

The human hear is able to detect CW signals even many dB
belove the noise depending on the operator ability.

Since the AO40 users are using RHCP on the ground, the 40' transmitting
antenna  should radiate a LHCP to the moon to get the best performance.

The moon will reflect to the earth a RHCP signal but the 40' dish must be
equipped with a feed for LHCP on TX and  RHCP for RX

If the 40' dish uses only linear polarization  the AO40 users will loose
3 dB on the above S/N ratio

Many AO40 operators are using dish with more than 1 meter in diameter
with very low overall noise figure systems and using very narrow filters
in the order of 250 Hz on CW the experiment seams to be succesfull.

73" de i8CVS Domenico


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