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Re: Looking for dish information



Hello This is Yoshi.

At 2001/05/12 20:21:39 Bob McElligott wrote:
> Can anyone recommend a good source for parabolic dishes (raw) for use with
> Mode S.

  If you have a time to go out to the electronics-shop at seoul-city,
maybe you can find 45-60cm Dish for BS receiver very commonly. I think
that most of them - even if that is offset type - will be OK for S-band
use.
  I am now using a TDK 45cm Dish for receiving S-band signal with modified
Drake2880.

Dish
  <http://plaza16.mbn.or.jp/~palau/images/tdkdish01.jpg>

Feeding System with dish.
  <http://plaza16.mbn.or.jp/~palau/images/tdkdish02.jpg>

Feeding System
  <http://plaza16.mbn.or.jp/~palau/images/tdkdish04.jpg>
  Prototype-1 : left. Fixed length.
  Prototype-2 : right.Adjustable length. - now testing.

  45cm is little bit small for AO-40 so that is better to look for the
old 60cm models at discount shop.


> What is the smallest dish size that will achieve good result on
> Mode L?

  A post of Mr. Edward R. Cole at 27th-April on AMSAT-bb said that the
front gain of dish will be calculated with this;

  Gain (dBi) = 10 Log ( e x 12.56 x (Diameter)^2 / (Wavelength)^2 )

  * Effectivity 0-1. usually use 0.5 for plain dish.

  I do not know how much the EIRP requirement is for L-band, but in
the case of 800W (JH1UGF's system on Lband) with 10W output, you need
19dBi gain. So;

  Diameter  Gain on 1269MHz
    1.2m      22.09dBi  |
    1.1m      21.33dBi  |
    1.0m      20.51dBi  |
    0.9m      19.59dBi  V Minimum requirement.
    0.8m      18:57dBi ------------------------

  So you should look for a bigger than 80cm diameter dish - for old CS
base stations or police/firedepertment use.

  But how this to make up the dish with mesh and alminum pipe? JA2DHB
made a dish for 1.7GHz weathersat receiving dish as below. This style will
be no problem on 1.2GHz or 2.4GHz!

http://homepage2.nifty.com/wsat/const.htm

  He said that the weight of dish (except holding L-angle and feed ) is
about 5kg (11 lbt.). It can be made from very common materials so maybe
you can find them in Korea.
  I have a plan to make this small (90cm) size copy for my portable AO-40
system.

  I hope this will help you.


Yoshihiro Imaishi JF6BCC/KH2GR
GL:PM53JV, ex KC6IY(T88IY),V63BP
mailto:jf6bcc@jarl.com or jf6bcc@jamsat.or.jp
<http://plaza16.mbn.or.jp/~palau/> Sorry, Japanese only now.
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