Re: [amsat-bb] TranSystem Mounting

["Mark L. Hammond" <hammond@xxxxxxxxxxxxxx>]

Hi Joe,

Well, I've wondered the same thing.  One of the other list members (he says 
he's shy ;-) said it should be about 14" or so.  Using the furthest out 
holes, it puts the little TranSystem reflector at 14".  My "intuitive 
mounting" originally put it at 12".  So, I moved it out to 14".

Here is a snip of our exchange:
------------------------------------------------
Take a look at pg 10-20 in Radio Amateur's Satellite Handbook.

The focal point is determined as follows:

f=D*D/(16*h)

where D is diameter and h is depth.

Just measure across the surface anywhere, making sure to go through the 
center. I used the corners, which were 43", and the depth was 8.25". This 
results in f=14.0".

I measured several points along the cross section and compared with 
theoretical. The max error is about 0.25". Based on maximum desired error 
of 1/12 wavelength, this is great.

If you mount the feed post such that the rear end is flush with the dish 
plate, the dipole will be at 10.25". This will result in substantially 
reduced gain.
----------------

My concern was that the dish isn't circular.  What I mean is, measuring 
top-to-bottom, side-to-side, or corner-to-corner all give different 
measurements, and corresponding depths.  However, the neat part is applying 
them to the formula gives about 14" no matter which sides you measure...(a 
little more using the side to side method..but still close to 14")

Is the reflector supposed to be 14" from the dish, or the little dipoles?

73,

Mark N8MH


At 03:30 PM 3/28/2001, Gary \"Joe\" Mayfield wrote:
>I notice there are 2 sets of holes on the mounting bracket for the
>downconnverter and 3 sets of holes on the downconverter itself.  This yields
>6 possible places to mount it.  I am sure I would choose the wrong ones.
>Does anyone know which holes to use?
>
>Thanks and 73,
>Joe
>ka0yos@amsat.org


Mark L. Hammond  [N8MH]

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