[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: 18" dish specs



> I'm finally building my downlink for AO40 and I'm trying to figure out the
> gain for a converted Dish Network dish (18" round) with a 5 1/4 turn helix
> feed.  Anyone got exact figures?

I measured 19 dbi using Sun noise on my 18 inch dish.  With a very good
preamp (<0.7 db NF) directly at the feed it is usable, but if you can swing
it, the extra 6db from a 3ft dish is well worth it.

> Also, which way (looking out from the
> feedpoint) should the helix turn, clockwise or counterclockwise?

I always manage to get it wrong when I try to describe it so here is a link
to a picture of my feed.
http://home.cfl.rr.com/lmclamb/dssfeed.jpg

The dimensions for the feed were shamelessly copied from K5OE's 16 turn
design with the winding direction reversed to use as a feed.  Basically the
feed is wound on 1 inch PVC.  The first 1/2 turn only 1/4 inch from the
reflector.  The remaining turns each have a spacing of 1 inch.

Good Luck,
Lee-KU4OS



----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home