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Re: Re: 2.4GHz S band helix feeds, et al.



ED,
A Air dielectric Patch feed works great on a F/D 0.35, A 4 turn Helix works
great on an F/D of 0.7.
Art, KC6UQH
----- Original Message -----
From: "Edward R. Cole" <al7eb@acsalaska.net>
To: <ka8syx2003@aol.com>; <AMSAT-BB@amsat.org>
Sent: Thursday, March 17, 2005 7:18 PM
Subject: Re: [amsat-bb] Re: 2.4GHz S band helix feeds, et al.


> Ray,
>
> I measured my HB helix feed which I use with an offset-fed dish.  It uses
a
> 3-inch square aluminum plate reflector and 1/4-turn matching stub (1/2 x
> 1-inch brass plate) followed by 5-1/4 turns.  Full length is ~ 4.5 inch
> long by 1.3-inch diameter using 1/8-inch solid copper wire.  The Wimo
Helix
> at 6-inches is near this so may work OK as a feed for an offset-fed dish.
> It is too long for a center-fed dish of f/d ~0.35 which most commercial
> dishes run.
>
> I would assume your Wimo helix has a 3-inch round reflector inside the
> radome at the rear connector, so why not give it a try.  I agree that it
> makes no sense for the Wimo to be built without a reflector or reflector
> ring element (alternate design).  Application for terrestrial WiFi is less
> concerned with ground noise pickup since strong signals are expected.
> Also, the antenna looks at the horizon anyway which rises the antenna
noise
> temperature.
>
> I am trying to remember your original post.  I believe you have a
Direct-TV
> dish which is an offset-feed dish, I assume.  I would try the Wimo feed
> with it placing the bulkhead directly behind the clamp (away from the
dish)
> on the arm of the dish.  The original feed clamp is probably not large
> enough diameter to hold the Wimo so just use a plastic wire-tie to
> temporarly hold it for testing.  It will work with a Primestar dish as
> well...you may have to experiment to find the best position at the focus.
> I have no experience with the Primestar to advise you on that.
>
> The BBQ dish is not a good candidate for using your Wimo helix.  If you
> want to make a feed for it, I would suggest a patch as they match the f/d
> of a BBQ better.  My guess is to stick with the Direct-TV dish or go with
a
> Primestar...lot less work and time spent than trying to convert the BBQ to
> circular polarity use.
>
> There were some suppliers of dish systems for AO-40, but I do not know if
> they still exist now that it is history.
>
> Try this reasoning with your wife:  "you will limit your ham activity to
> equal their shopping time at the mall" :-)
> Seriously, you cannot win this, so don't even try.  Just remind her you
are
> home and not out chasing other women (or boosing at the local pub) when
you
> "ham it up"!
>
> GL & 73's
> Ed
>
> At 12:24 PM 3/17/2005 -0500, ka8syx2003@aol.com wrote:
> >Ed, Bob,
> >
> >Thanks for your comments.  The WiMo helix doesn't look very long, in
> comparison to some hb helices I've seen in various references, and not
> nearly as long as a regular helix antenna for MMDS or similar appl on S
> band.  With radome and all, it's only about 6" in length from the rear
> bulkhead to the forward end of the radome and about 3" in diameter.  Would
> it be worth the effort to hb a reflector and just attach it to the rear
> bulkhead, or must it have that 1/4" wide shim on the first 1/4 turn of the
> first winding about which I've read?
> >
> >In a roundabout way I guess I'm asking you two, and other bb readers as
> well, if I've wasted about $100 on a helix feed I can't use.
> >
> >Why would a helix feed like the one I have be on the market without a
> reflector?  Are there applications for one where the user wouldn't be too
> concerned with background pickup?  If I am almost exclusively interested
in
> receive capability on mode S, the reflector is aimed at an upward
elevation
> and the feed is pointed at the reflector to capture maximum signal so that
> nothing is aimed at the ground, do I need to be worried about the
reflector?
> >
> >Lastly, if the feed I have is no good and cannot be successfully
> integrated with a PrimeStar dish as Bob suggests, does anyone offer for
> sale a helix or patch feed for mode S that can be used with the AIDC 3731
> and a parabolic in the 60cm dia x 25cm depth area?  That's the approximate
> size of the large BBQ dishes I have on hand and was going to enclose with
> screen if I couldn't make the DirecTV dish work.  I haven't a lot of time
> to experiment, nor funds to spend on a bunch of test gear, so I'd really
> prefer something that works COTS.  It's not that the physics of this is
> totally beyond me, just that my resources to play on the radio are limited
> and my threshold for frustration is low.  What is it about spouses?  They
> think you can accomplish your radio goals in 15min a day!
> >
> >73, Ray KA8SYX
> >----
> >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!
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> ----
> 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!
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----
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