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Re: Helix feed details



The N-connector needs to be well grounded on all sides. The washers probably
look like small inductors at 2.4 GHz. I make spacers from 0.030" or 0.060"
aluminum with 5 holes drilled for the mounting screws and center conductor.

73,

John
KD6OZH

----- Original Message -----
From: "David Rush" <ky0dr@earthlink.net>
To: <amsat-bb@AMSAT.Org>
Sent: Thursday, 14 June 2001 21:39 UTC
Subject: Re: [amsat-bb] Helix feed details


> Greg:
>
> Here's what I did.  I think I understand the "bump" on the "panel" side of
the N connector that you're talking about.
>
> I first discovered the bump after I drilled a hole in the reflector large
enough for the pin of the N, but realized that the screw holes
> wouldn't touch the reflector because the bump kept it from laying down
flat.
>
> I used a reamer to enlarge the hole such that the bump fit through the
hole and the mounting screw holes laid flat on the reflector.
>
> But yes, the 1/4 turn matching section was too far away from the
reflector, so I used washers between the reflector and the N
> connector to pull the N connector back a bit.
>
> Then a friend came over with an antenna analyzer that would do up to 3
GHz.  We experimented with the spacing, and found the
> greatest return loss (best match) with zero washers in place, and the
matching section much farther from the reflector than the G3RUH-
> spec distance.  So I left it there.
>
> Here's what mine looks like, on a PrimeStar dish:
>
> http://www.draig.org/gallery/200106/20010612a-webpic-021.jpg
> http://www.draig.org/gallery/200106/20010612a-webpic-022.jpg
> http://www.draig.org/gallery/200106/20010612a-webpic-023.jpg
>
> I ended up putting the washers behind the N connector, just to keep my 1/4
inch screws from protruding too far out of the reflector.
>
> David, ky0dr
>
>
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