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Re: Dish questions for 2.4GHz and 24GHz




I wish people would look on the web once in awhile for info before
going into a long discussion like this, almost all questions like this can 
be answered by looking at either the manufacturers site, or Google, 
Altavista, etc...

>From the DH website:  http://www.dhsatellite.com/Efficiency.htm

"Reflectors are Manufactured on an Automatic Spinning Machine using a
machined steel mandrel.  DH Guarantees an RMS surface accuracy of .020
of an inch to the parabolic curve."

So at K-band that translates into 1.133 dB loss (from the gain of the dish 
at K band) which should still be more than 40 dB for even the
small dishes.

The 1.2m dish has a stated gain of 42.2dB at 12 GHZ-- at 24 GHz this should 
be 6 dB greater (area of the dish compared to wavelength is 4 times the 
size-- think of a rectangle with each side being twice as big, four times 
the area results.)

Even though the 42.2 dB@12 GHz is with the RMS inaccuracy taken into 
account, I'll subtract the whole 1.133 dB from the equation.

42.2 dB + 6 dB = 48.2 dB - 1.133 dB = 47.1 dB gain (minus feed inefficiency) 
  So in practice you will get better than 40 dB of gain
out of the 1.2m (4 foot) dish from DH at 24 GHz.  Pointing this
dish will be the bigger issue! Maybe a 2' dish specifically for K would be 
better. I think DH can UPS dishes <3'.

Going backwards, at 2.4 GHz, this is roughly 4x the wavelength of Ku band 
TV-- so the dish should have around 30 dB of gain at 2.4 GHz. (Consistent 
with what I'm seeing)...I've determined beamwidth by armstrong pointing and 
I'd say that the 3 dB BW is around 8 degrees.  So at 24 GHz.. hmm that be 
less than 1 degree...

The 4' DH dish that I have is pictured in my "Rube Goldberg AO-40" page-- 
I've had it for years.  I left the mount and the struts 250 miles from where 
I currently live, and will get them eventually, but in the meantime I'm 
operating like this:

http://members.home.net/fspinner/W0FMS/rubeao40.html

Fred W0FMS


>From: "James R. La Frieda" <lafrieda@earthlink.net>
>To: "Don Woodward" <dbwoodw@abraxis.com>
>CC: <amsat-bb@AMSAT.Org>
>Subject: Fw: [amsat-bb] Dish questions for 2.4GHz and 24GHz
>Date: Thu, 20 Sep 2001 23:55:36 -0700
>
>
>Don,  If the RMS surface tolerance of your DH Satellite dish is very small
>compared to the operating wavelength - and since it is made of aluminum - 
>it
>should be - you shouldn't lose too much gain using it at 24 GHz with an
>appropriate 24GHz feed.  At 24GHz, corresponding to a wavelength of 1.25cm
>or .492 inches, you will have the following loss in gain performance:
>
>    RMS surface tolerance        Gain Reduction
>  .005 inches  or .127 mm          .071 dB
>  .01 inches    or  .254 mm        .283 dB
>  .02 inches    or  .508 mm        1.133 dB
>  .03 inches    or  .762 mm        2.549 dB
>  .04 inches    or  1.016 mm      4.531dB
>  .05 inches    or  1.27 mm        7.1dB
>
>Thus, to be on the safe side- if you are interested in using the dish for
>24GHz, contact DH Satellite and ask them to tell you what is the RMS 
>surface
>tolerance of the dish you are purchasing. If they tell you that they don't
>know- find yourself another dish manufacturer who knows and who can
>guarantee what they manufacture - for as you can see above- with a
>.05 inch rms surface tolerance - you will give up 7.1 dB gain at 24 GHz.  
>On
>the other hand , this same .05 inch rms surface tolerance at 2.4 GHz yields
>a gain reduction of  only .071 dB
>
>All the Best,
>Jim, N6MV
>
>----- Original Message -----
>From: "Don Woodward" <dbwoodw@abraxis.com>
>To: "amsat-bb" <amsat-bb@AMSAT.Org>
>Sent: Thursday, September 20, 2001 7:03 PM
>Subject: [amsat-bb] Dish questions for 2.4GHz and 24GHz
>
>
> > Would the dish below from DH Satellite be suitable for 2.4GHz now and 
>then
> > be adaptable to 24GHz later provided substitution of two correct feed
>mounts
> > and feeds?
> >
> > Don Woodward
> > KD4APP
> > AMSAT 33535
> > kd4app@amsat.org
> > sales@sunsunsun.net
> > www.sunsunsun.net
> >
> >
> > ----- Original Message -----
> > From: Michael Doll
> > To: dbwoodw@abraxis.com
> > Sent: Thursday, September 20, 2001 11:56 AM
> > Subject: Antenna
> >
> >
> > Attn: Mr. Woodward
> >
> >     Thanks for your email.  We manufacture a 48" (1.2m) antenna.  This 
>has
>a
> > focal length of 22" and an f/d ratio of .45.  This is a one piece 
>antenna
> > and is made from solid aluminum.  When shipping one at a time this is an
> > expensive piece.  If we can deliver it with our truck to your area you
>would
> > save both on the freight and the packaging.
> >     The 1.2m antenna with mount sells for $142.00 this includes the
>painted
> > antenna, complete polar mount with feed collar and struts and stainless
> > steel hardware.   Crating will be approx. $30.00 and it will have to go
> > truck freight.  Contact me with any questions.
> >
> > Michael Doll
> >
> > ----
> > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
>
>----
>Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
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