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Re: AO-51 mode V/S



----- Original Message -----
From: "francesco messineo" <francesco.messineo@gmail.com>
To: "George Henry" <ka3hsw@earthlink.net>
Cc: <amsat-bb@AMSAT.Org>
Sent: Wednesday, May 14, 2008 9:09 AM
Subject: [amsat-bb] Re: AO-51 mode V/S

> Hello,
>
> On 5/13/08, George Henry <ka3hsw@earthlink.net> wrote:
> > You can use any oscillator module, such as from an old PC motherboard,
that will put out harmonics up in the 2.4 GHz range.  I happened to find a
24.000 MHz one on an old MB.  Just now, looking around in the junk drawer, I
found ones for 4.000 and 16.000 MHz as well.  Add 5 volts and a short piece
of wire on the output pin, and you're good to go.
> >
>
> I can confirm, I used a 50 MHz xtal oscillator and I have a very
> strong armonic signal at 2400 MHz.
>
> hth
> 73
> Francesco IZ8DWF

Hi Francesco, IZ8DWF

To test if your 2400 MHz receiving system is suitable or not to receive a
satellite signal you don't need a strong armonic signal because  a XTAL
signal source tell you only if you are correctly in frequency but very
small in sensitivity of your receiving system because in general the output
power of the source is too high and uncalibrated.

My XTAL signal source (G0MRF type) feeding directly a half wave
dipole has an output power of - 28 dBm measured at 2400.408 MHz

The overall noise figure of my receiving system is 0.7 dB equivalent to
a noise temperature Te = 51 kelvin
When the elevation of my 1.2 meters dish is zero degrees the feed get a
noise level from the ground of about 290 kelvin
In this condition the equivalent noise temperature Tsys of this receiving
system  is 51+290 = 341 kelvin and the calculated noise floor with the IF
receiver switched to SSB in a BW of 2500 Hz is  -139 dBm

With the above sensitivity if I plan to receive with a S/N= + 15 dB my
- 28 dBm signal source connected to a dipole while  using my 27 dBi dish
I must put my signal source  in a free line of sight about 20 km away from
my dish as calculation shows.

Please note that a received signal of + 15 dB over the noise is a very
good signal for SSB as tell the experience with OSCAR-10, OSCAR-13
and AO40

Power of  Signal Source ...................   - 28.00 dBm

Gain of  Signal Source dipole...........   +  2.14 dB
                                                               -------------
Signal Source EIRP...........................   -  25.86 dBm

Attenuation 2.4 GHz over  20 km.....  - 126.00 dB
                                                                ------------
Power received on isotropic ant......... - 151.86 dBm

Gain of 1.2 m dish.............................. +  27.00  dB
                                                                 -----------
Available power at RX input.............. - 124.86 dBm

RX noise floor with ant. connected..   - 139.00 dBm
                                                                 -----------
S/N ratio of received signal..............   +  14.14 dB


I hope this helps

73" de

i8CVS Domenico






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