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Re: Ao40 , negative 13cm RX attempt.



William Leijenaar wrote:

> Hi AMSATs,
>
> 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.

Is it 12 or something higher?  Most people have reported that the downconverters
work poorly with only 12 volts up the coax.  Aim for more like 18.

> 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.

Massivily too little antenna!  Your dipole, double quad, or 3 turn helix are
good possibilities as a feed for a dish, but alone, they are not even close to
enough antenna!

> All these radiators I tried without dish as the satellite was very close to
> the earth, what gave no result.

Actually you will likely find better signals near apogee.  The squint angle is
the key factor.

> I also tried all the feeds with an 60cm dish, with also no result.

60cm is about the smallest dish you can get away with and that with a much
better downconverterr than the NorSat.

> 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'm using a 2 x 3 foot solid offset fed dish with a modified TranSsytem 3733
downconverter.  I consider that to be acceptable, but far from ideal.  I have no
trouble hearing strong signal stations, but weaker stations sometimes get lost.

> I also seen two kind of frequenties.  2401.300  and 2401.323

2401.323 is the place to be.  Remember that your downconverter could be WAY off
frequency  Look up to at least 200 KHz off freq.  Also, many are rather
temperature sensative.  I found mine is pretty good if I leave it on all the
time.

> Another reason could be that 13cm was turned of...

The beacon is off from MA 70 to 87.  The rest of the orbit, it's on.


73
-----------------------
Jim Walls - K6CCC
k6ccc@amsat.org
http://home.earthlink.net/~k6ccc/
626-302-8515    FAX  626-302-7501
AMSAT member 32537 / WSWSS member 395


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