[Moon-net] 2.40m dish
Paul Wade W1GHZ
q.w1ghz at verizon.net
Mon Sep 29 03:07:56 CEST 2008
think for a moment - why should loss travelling through space vary with
it doesn't! it's just that pathloss is defined between isotropic antennas,
decreases with frequency. for a constant aperture area, pathloss is also
with frequency. so if a 10 foot dish works at 1296, it will also work at
10 GHz, if
you have the same NF and power (which might be a problem).
At 02:48 AM 9/27/2008, Edward Cole wrote:
>For what its worth, I wonder if any out there have looked at the eme
>pathlink as frequency increases? Pathloss rises by the square of the
>frequency and so does dish gain by square of diameter. So a ten foot (3m)
>dish should work as well at 10-GHz as it does at 1296. From what I have
>gleaned from reading, ten foot is the minimum "standard" for CW.
>Opting for an 8-foot dish (2.4m) reduces gain by 20Log (8/10) or ~ 1.9 dB
>down from a 10-foot dish. That being said one would expect the same
>performance if sky noise, preamp NF were the same. But it seems that the
>smaller dish does just a bit better with higher frequencies. Could this
>be due to slightly lower sky temperature? Or is it because the Moon is
>better illuminated by the smaller beamwidth?
>Ironically, today my wife tells me that there is a 14-foot mesh TVRO dish
>available in our neighborhood for the taking. Since I have two 1.8m, a
>2.4m, and a 4.9m dish, I certainly need another one ;-) I will probably
>retrieve the 14-foot dish if only to hold for some future eme'r or amateur
>Re the 4.9m dish: We are fabricating and welding the az-el mount
>tomorrow. This mean we should have the dish installed in about two
>weeks. Give me two more weeks for installing feed, running cables and 60w
>PA at the dish.
>73, Ed - KL7UW
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