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R: R: AO-40 spreadsheet



Hello Doug,

My system for 2400 MHz uses a full aluminum 1,2 meter dish with F/D=0,45 and
28 dBi gain at 2400 MHz with 50% efficiency.

The feed is a 3 turns LHCP elix made of silver plated 3 mm copper wire with
a measured  25 dB  return loss with the elix in place at focal point.

In this condition the -3dB main lobe is 7° and the spillower from the 3
turns feed is the best compromise between gain and - 10 dB illumination of
the dish at  the edge.

The focal point of the dish has been placed inside the elix , 25 mm apart
from the elix reflectors using cut and try in order to get  a good phase
center for maximum measured gain and side lobe riduction
compromise.

The low noise preamplifier is a home built WB5LUA (PCB from DEM) with a
PANFI measured NF=0,65 dB and G= 13 dB

The WB5LUA LNA is directly connected to the SMA elix connector interposing
in bethween a low loss 0,2 dB SMA coax relay up to 12,5 GHz because the
system was designed for the 2400 MHz uplink as well and it has been built
with a 10 W 2400 MHz  linear amplifier wich unfortunately will not operate
with AO40

The WB5LUA LNA output is connected to a postamplifier input via 1,5 meters
long semirigid UT-141 coax cable with 1 dB loss al 2400 MHz

The postamplifier is installed in to a big plastic box wich is mounted
behind the dish along with transverter and power amplifier.

Postamplifier uses a MGF-1302 GaAs FET and is built in to a machined silver
 plated brass  box with input and output tunable 2400 MHz copper resonators
providing  good selectivity with NF= 1,2 dB  , G=16 dB  and its
conditionally stable.

The output of this postamplifier is connected to an interdigital filter with
1 dB insertion loss at 2400 MHz and 60 dB attenuation on the image frequency
of 2112 MHz and this filter is the heart of the system.

This very small filter was described by KK7B in "Proceedings of the 1296 and
2304 MHz Conference,Estes Park,Co.Sept 1985

The output of the interdigital filter is connected to the input of a DB6NT
2400-2402 MHz transverter via an SMA 2 dB fixed attenuator to let the filter
see close to 50 ohm and keep the transverter stable.

The transverter DB6NT is home made using a modified KIT originally developed
for 2304 MHz or 2320 MHz and its NF=1,5 dB with G=20 dB and,very important
an image 2112 MHz rejection of 40 dB can be obtained for optimum SSB noise
 figure of the system.

The overall noise figure SSB measured with PANFI on the banch is 1,25 dB

Preparing for the future,the complete 2400 MHz downlink-uplink station was
described and published in Radio Rivista,the,official italian radio magazine
of ARI in the following issues:
May/95, June/95, Nov /95, Dec/95, Jan/96, Feb/96, March/96, May/96
Radio Rivista is ISSN 0033-8036

In my below previous message i was wrong and the correct phrase is:

>>  if  i get a sun noise (S+N)/N=5 dB i must be happy................

73 de i8CVS Domenico


----- Original Message -----
From: Douglas Braun & Nadia Papakonstantinou <doug@dougbraun.com>
To: i8cvs <domenico.i8cvs@tin.it>
Sent: Monday, May 28, 2001 3:36 PM
Subject: Re: R: [amsat-bb] AO-40 spreadsheet


> You obviously have a very good system!  What are you using?
>
> Thanks,
>
> Doug
> NA1DB
>
> At 05:26 AM 5/28/01 , you wrote:
>
> >My system sun/sky (S+N)/N is 5 dB at 2400 MHz  and under this conditions
i
> >get the AO40 transponder noise at apogee with at least  3 dB of (S+N)/N
or 0
> >dB of S/N but normally much more.
> >If i get a sun noise (S+N)/N=3 dB i must be happy because any increase of
> >antenna gain or any reduction of the overall receiver noise figure is not
> >necessary.
>
>










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