Re: [amsat-bb] ao-40 antennas

["Edward R. Cole" <al7eb@xxxxxxxxxxxxx>]

>X-From_: joe@xyz.net  Sat Aug 11 14:58:31 2001
>Hi Vince,
>
>I'd echo that!  I started with a home brew 20 turn helix, about 16 dBi, and 
>it didn't work very well.  I'm looking for a dish now, while using a BBQ 
>grill loaned to me by Mike, WL7BQM.  In fact, Mike and I both are 
>considering buying a dish from the same company (Down East Microwave) to 
>save on shipping costs. That should improve S2 dramatically, and with S1, 
>you probably won't even need a radio to hear it!  ;-)  We're considering a 
>home brew 3 turn helix as a feed for the dish - not sure about the dBi 
>gain, but it would sure beat whatever linear feed system you may be using.
>
>73,
>Joe
>WL7M
>Fritz Creek

A 3-foot dish at 55% feed eff. on 2400 MHz has 25.7 dBi gain and a
beamwidth of 9.7 deg.

AO40_S2 spreadsheet shows that with 3-foot dish, cir. pol., 0.6 dB NF you
will see the beacon at 29.6 dB S/N at zero squint, and the  xponder noise
floor out to ~10 degrees squint.  At a squint of 30 deg. the beacon S/N is
still 17 dB and you would have fairly good copy of stations -10 dB from the
beacon.

A 1 dB NF reduces this to barely detecting the noise floor at zero squint
[beacon S/N of 27.5 dB], and at 30 degrees squint the beacon is 15 dB S/N.

Ed

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