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

Re: 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!
>To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
----
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