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Re: Ao40 , negative 13cm RX attempt.


The signal for AO-40 would not be classed as strong.  You need a min. of 22
dBi antenna gain and a system noise figure under 1.5 dB.  Better is having
at least 24 dBi gain and 0.7 to 1.0 dBNF.  So this implies a dish of at
least 60 cm and better to have 85 cm or 1m.  Some have heard the beacon
using just a large helix (23-35 turns), but for adequate performance to
work stations which are to stay 10 dB weaker than the beacon, you need a dish.

The Norsat convertor probably has too high a NF (I am not personally
knowledgeable about it).  I have been preaching for a year that you need to
use a low noise preamp for AO-40.  The only converter that seems to be
adequate by itself is the UEK3000.  It has 0.7 dBNF and over 30 dB gain.
The feeds you describe should work with a center-fed dish.  If the dish is
an offset feed, then better luck is obtained with a 4 to 5-turn helix feed
with reflector disc.

One of the problems people have starting out is they have no way to check
the frequency of their converter.  None of the commercial units are exactly
on frequency, so you need a signal source of know frequency to calibrated
the converter.  The rest frequency (zero Doppler) of the beacon is
2401.323.  Doppler can shift this up/down 25 KHz.

Do not be disheartened.  Nearly everybody has run into the same
difficulties hearing the satellite at first.  I hope my letter has helped.
I wrote a paper about what is needed to get on AO-40 for the 2001 Amsat-NA
Symposium and is available in the proceedings.

Good Luck,

At 12:23 AM 11/19/2001 +0100, you wrote:
>The past weekend I have tried to hear the AO40 for my first time.
>Unfortunatly the only thing I've heared was the famous noise :-(
>I tought the 13cm AO40 signal is very loud, but somehow for me it was like 
>Mars signals haha. (I can not RX these signals ether)
>I used an modified NORSAT 13cm-->2m convertor as downconvertor. The 2m is an 
>FT726 with 12V DC via the coax to the downconvertor.
>As antenna I have tried several self-made designs like dipole, double-quad 
>with/without reflector, and 3 turn helix.
>All radiators I have tested the VSWR and tuned at maximum effeciency.
>All these radiators I tried without dish as the satellite was very close to 
>the earth, what gave no result.
>I also tried all the feeds with an 60cm dish, with also no result.
>Then I stopped the experiment because it got to cold outside, and I will 
>start again with the experiment after I know if this AO40 is really very 
>loud and realy recievable with this NORSAT downconvertor without pre-amp. 
>Maybe this NORSAT convertor is just to deaf to hear even an very little 
>signal of Ao40 ?
>Maybe someone can give me an idea what kind of antenna/RX equipment I need 
>to get an low/medium class AO40 station ?
>I also seen two kind of frequenties.  2401.300  and 2401.323
>I guess the second is the freq. after launch... ?
>Another reason could be that 13cm was turned of...
>That would be just bad luck :-)
>73 de PE1RAH, William
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