I have gotten good reception using a signal generator with -20dBm output on 800-MHz to a simple diode paralleled by a 47-ohm resistor mounted in a coffee can placed 20-feet from my dish (my receive system is very close to Franscesco's in performance). I used about 40-foot of RG-58 for the 800-MHz signal so that dropped the signal another 13-dB or so. The third harmonic would be less than 1/3 the power of the 800-MHz signal.
73 Ed - KL7UW
At 05:16 AM 5/14/2008, i8cvs wrote:
----- 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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