[TowerTalk] Very Old Grease Characteristics

[Jim Lux]

At 03:48 PM 12/20/2006, Michael Baker wrote:
>Hi Pat,
>         WOW, a 30 METER DISH!  Man, to feed a gallon of 1296 energy into
>that towards the moon should be hearable!  FM on a HandHeld would be
>readable!!


Well, perhaps not quite that.  A 30m dish at 23cm wavelength is about 
49-50 dBi gain
The free space path loss (one way) to the moon is about 200 dB at 
that frequency.

The beamwidth of the antenna is about 2 degrees, and the moon is 
about 1/2 degree wide, so the moon intercepts about 1/16th of the 
power you send to it.  Assume, for the moment, that ALL that 
intercepted power is radiated as if it were an isotropic source, and 
you just pick up the part that shines on you.

So, a quick link budget:

1500 W radiated to moon ( +62dBm)
1/16th reflected back (-12 dB)
free space path loss (-200 dB)
receive antenna gain (+50dB)
power into your HT.. -100dBm
Is that hearable?
Front end NF of, say, 3 dB, so power spectral density is -171 dBm/Hz
Bandwidth of 10 kHz (40dBHz) for example
Noise power is -131 dBm
Signal power is -100 dBm
SNR of 31 dB.... you'll hear it.

But, if your receiver is just that HT with a 10dBi Arrow antenna or 
similar.. you've got 10dBi instead of 50dBi antenna, so the signal 
power is 40dB lower... -10dB SNR...  But, in a 500 Hz BW, etc., it might work.

Also, I'm not sure my assumption of 0 dB for the moon's backscatter is valid.


(One also has to come up with a high power 1296 amp)