# Re: DISH BEAM WIDTH--corrections

• Subject: Re: [amsat-bb] DISH BEAM WIDTH--corrections
• From: "Edward R. Cole" <al7eb@xxxxxxxxxxxxx>
• Date: Sat, 01 Mar 2003 07:23:51 -0900

```oops...I goofed on the f/d calc (to used to 10-foot dishes I guess)
f = (144)^2/16*22 = 20736/352 = 58.9
diam = 144
f/d = 0.41
WL = 300/freq = 0.13 m
freq = 2400 MHz

sorry was sleepy and late at night...someone take my calculator away ;-)
There may be more accurate calculations of beamwidth but this is a good
approx.
Other calculations correct, I believe.

Ed
-------------------------------------------------

>Bill:
>
>G(dB) = 10Log [4*pi*e*diam^2/WL^2]
>pi = 3.1459
>diam = 12/3.28 meters
>WL = 300/2400 meters
>e = 0.55  {55% dish effficiency}
>
>f = diam^2/16*d
>d = dish depth
>
>HPBW = 57.3*WL/Diam
>
>d = 22 in
>G = 37.4 dBi
>HPBW = 2.04 degrees
>f = 40.9 in
>f/d = 0.34
>
>Ed - AL7EB
>
>At 12:24 AM 3/1/2003 -0500, walnuthil@juno.com wrote:
>>Hello All,
>>I recently acquired a TVRO 12 foot dish, with the mesh
>>reflector. I have been trying to calculate the 3db beam width
>>in degrees, the books I have are not clear on the formula.
>>Does anyone have the correct math formula ?
>>Putting a 2 by across the dish and measuring down the
>>center is 22 inches. Yields a f/D = 4.0 if the formula is right.
>>I plan on using it for receive on AO-40, I have some tall pine
>>trees to the south that reduce the down link signal.
>>Hopefully this dish will help.
>>Bill
>
>>WA1DMV@amsat.org
>>#20942

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