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Re: Mode-S Antennas



Hi Mark.
n0nsv@AMSAT.Org writes:

> Well now that so many of us have our Drake 2880 downconverters and our
>  crystals are on the way, I'm interested to know how everyone plans to
>  get a signal to it. What is the consensus for a good 2.4ghz antenna?
>  Helix, dish, yagi? 

I just put a new small dish crafted by Kevin, N3HKQ, on the Home Brew Picture 
Album:
http://members.aol.com/homebrewpics

It is a 60 cm dish using a G3RUH helix feed and a Parabolic AB downconverter.

Anyone know where those old aluminum snow coasters are still sold?  I built 
some MMDS downconverters in the early 80's using those, but have not seen 
them in a decade.
  
>  Personally, I'd like to find another Conifer Dish like Myers used to
>  sell. I had one but it got mangled due to the effects of sudden
>  deceleration. Prices became way out-of-line (my opinion) when Andrews
>  bought the company so I'm looking for an alternative. 

You are not kidding.  Those dishes have been going for around $90 on eBay 
lately.

>  Homebrewing isn't
>  an option for me, I'm all thumbs and my last project made the mangled
>  Conifer look like a masterpiece. 

Pretty doesn't count for much.  Take a look at the 16-turn helix on my web 
page:
http://members.aol.com/k5oe

...or the legendary G3RUH article:
http://www.amsat.org/amsat/articles/g3ruh/117.html

It is a mediocre antenna for receiving the AO-40 beacon in it's present 
state, but I believe (hope) it will be more than adequate when the bird is 
turned around, using the high-gain antenna, and using full power.  It really 
is a 1 hour job to build one using only simple hand tools.  If nothing else, 
you can build one while waiting for the crystal :-)  it will let you test the 
Drake while you wait for a decent-priced commercial antenna.

If you are interested in a Yagi (might not be a bad bet considering the 
wideband nature of the downconverters and the potential noise sources on 13 
cm), check out the DEM loop Yagi's in 3', 6', and 12' models:
http://www.downeastmicrowave.com/Antennas.htm

They also sell a small helix, for a whopping $175:
http://www.downeastmicrowave.com/dsh23-12.htm

73,
Jerry, K5OE
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