[amsat-bb] Re: 2.4 GHz Feed copied from the Mars Viking Lander

[K5OE@xxxxxxx]

Thanks, Pieter.  Very interesting!  Yes, that is exactly the configuration I 
tried.

For those on the BB that did not see the original note, I cobbled together a 
K&W style helix reflector "cup" and tried it out on local MMDS.  The cup is 
approx.  4" in diameter and 2" in height and mounted it on my default 16-turn 
helix I have been using for AO-40.  The improvement in signal quality was 
noticeable and I have no reason to believe the Trueman, Emerson, et. al., 
delta of 2 dB for this "mod" to be fairly represented by my little trial.  I 
plan further experiments.  You can see a picture of the lash-up at:
http://members.aol.com/k5oe/helix_cup.jpg
73,
Jerry, K5OE
ps:  yes, it's a coffee can :-)

elpieter@hotmail.com writes:

> The quad array looks good. I'm sorry to hear that it is not performing well
>  yet. I am sure you'll get it working good. I am going to build my antenna 
to
>  allow adjustment of the separation. Right now I am working on the phasing
>  harness. It's turning out to be relatively hard to keep the phasing 
perfect.
>  I plan on keeping the cables and split within 3 degrees at 2401.
>  
>  On another tangent:
>  
>  I recently visited the Air and Space museum in Washington. I took all of my
>  camera equipment with me. I focused on taking as many pictures of antennas
>  as I could hoping that I could reproduce some of them for 2400 MHz. One of
>  the most interesting ones was the antenna on the Mars Viking lander. This
>  antenna is about 1 meter in diameter and uses a helical feed. They use
>  something similar to my copper tape method and use a reflector like Jerry 
is
>  testing. I took a hi-res scan of the negative and here is the picture:
>  
>  http://www.ozoni.com/n4ip/viking.jpg
>  
>  I took the picture at an angle that allows measurements to be made. The
>  exact diameter of the dish is available on the internet. I plan on getting
>  this info for you.
>  
>  I believe the helix is wound on a Bakelite or fiberglass form with about 
1.1
>  inch diameter. That would make the reflector about 2.5 inches. I was trying
>  to get as close to the antenna and everyone was looking at me funny. It
>  helps to be 6'7" to be able to get over the plexi-glass protector.
>  73's
>  
>  Pieter Ibelings
>  N4IP
>  
>  Here's a picture of the whole spacecraft:
>  http://mars.jpl.nasa.gov/mgs/target/viking.gif
>  
>  
>  Check out these papers on antenna links with spacecraft.
>  
>  http://arnaud.labouebe.free.fr/Satellite.html
>  
>  http://deepspace.jpl.nasa.gov/advmiss/sdsmt.pdf
>  
>  
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