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receiving system design tradeoffs



Fred W0FMS wrote:

The difference between my BBQ and even my 2 foot
prime focus w/patch is about an S-unit.  An S-unit is 
a lot on  AO-40.  For me that was the difference between
struggling to hear the bird and having enjoyable copy.

Could I make that up by getting myself a sub 1dB converter?  
Yes.  It is  worth $300 to me to do this?  No.

Wayne replies:

I mostly agree with you, but the "system" for most of us is much more than just the dish and the feed.   Wind loading significantly affects the cost and reliability of the mounting structure and the rotor.

A 3 foot dish has more than double the wind load of a 2 foot dish.  A $300 downconverter (or better yet, a $120 preamp) allows you to use a smaller dish than would be required with a Drake downconverter.  A smaller dish is more likely to be suitable for a Yaesu az-el rotor, and doesn't require as elaborate a mounting structure.

My home AO40 receiving setup is a 23 inch diameter G3RUH dish, G3RUH patch feed, DEM preamp (0.7 dB NF), and a cheap TSI downconverter.  The dish and 10-foot VHF/UHF yagis are on a roof tripod with a G-5500 rotor.  A 3-foot dish would overload my rotors and force me to upgrade the mounting structure.

Wayne Estes W9AE
Mundelein, IL, USA

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