Simple
Downlink Path Loss Calculations for AO-51
Update
September 2007
I am just calculating free-space pathloss, and converting it to S/N (Signal to
Noise Ratio) above the RX sensitivity.
This assumes there is no antenna gain on the
receiver (earth station / downlink)
·
With a ~0 dB gain antenna (say a dipole with feed line loss), you
can hear the AO-51 down to ~20 degrees.
o This is possible
and has been verified by me multiple times… I have made numerous mobile contacts.
o My first contact
on AO-51 I used a homebrew 70cm dipole on a high pass.
·
If you want to hear the satellite lower in elevation, then use a
directional antenna.
·
With ~10 dB gain antenna, I have heard AO-51 down to ~5 degrees.
Shack RX sensitivity = -122 dBm
- With an LNA, you could probably add about 10+ dB to the
S/N ratio!
- From my "experience", this seems to be
about correct
- With an LNA, I was able to hear AO-51 with a vertical
dipole at ~10 degrees where as without it I heard nothing at this
elevation.
- You can purchase a pretty-decent LNA used for under
$15, and it will make a world of difference
Transmit Power for is AO-51 =
500 milliwatts ( 27 dBm)
Just remember you
can hear AO-51 with a simple antenna above 30 degrees.
Below
is a graph of the duration of the pass.
The higher the pass, the longer the duration, because it will be
in the sky longer.
Conclusion : it is possible work
some of the LEOSATS with simple antennas.
- I and others have done this!
- Beams just make it more fun!
For more information on calculating the Link Budget for AO-51 check out the AMSAT Link
Budget Page.