Re: [amsat-bb] 1269 uplink dish size ?

[Reinhard Richter <r.richter@xxxxxxxx>]

Hello Keith,

Thursday, January 22, 2004, 1:02:04 PM, you wrote:

> Just letting my mind wander off on a tangent from my previous ideas!! and I
> was wondering given a power of 10 watts at the dish or 10 watts in the shack
> and a coax feed of 15 mtr max what would be the minimum size of dish
> required for successful uplink to AO-40 on 1269 mhz?

I guess 15 m of coax will give you 3 dB loss. So only 5 watts will arrive
at the antenna feedpoint. This will not be sufficient with even an 1.2 m
dish. I have just put up an 1 m dish (see update on my homepage) and I am
feeding 70 watts into the line. Have also 15 m of coax. This produces a
good audible signal if squint is below 15°.

> I can get hold of 1.2mtr, 90 cms or 60 cms dishes relatively easily  (
> offset feed type only )

For an offset dish you most probably need a helix with 6 turns. A patch
will not illuminate the dish sufficiently.

Using the excel sheet "dish design.xls" by Gene Marcus
(http://home.hiwaay.net/~mmarcus/download/)
you can calculate the gain of a given dish:
The results are:
60 cm = 15 dBic
90 cm = 18.5 dBic
120 cm = 21 dBic
200 cm = 25.5 dBic
300 cm = 29 dBic

Then you can perform a linkbudget calculation which you can download from
the same page under "ao40v2.0.xls". Enter your figures into the L1 uplink
calculation and see the result. 60 cm dish will produce a rather weak
signal, while a 3 m dish will produce a more than sufficient signal. But
you should make the calculation by yourself, it is really eye opening!

BTW, recently the AO-40 coverage was very favourite for VK6 land with a
window to Europe during your local late evening hours. I was on each time
when there was a window, and I have worked several JA stations for whom
the local time was after midnight, but I haven't heard any VK6.
So hw?

73,
 Reinhard
 DJ1KM                            
www.dj1km.de


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