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Re: Ao40 , negative 13cm RX attempt.



A good start for me was using a 32" offset feed dish coupled to a Trans Systems
AIDC 3733 Downconverter for my downlink. The 3733 provides lots of gain, so coax
length and quality is not a major concern. I am getting the MB about S7 with the
bird near maximum range and a low squint angle, with a noise floor typically of
S2 to S3 with my FT-736. I can probably improve on this figure a bit by going to
helix feed for the dish, which should happen pretty soon.  I have added a Murata
filter to the 3733, which cuts out some of the local image noise as well. K5GNA
is your source for all things 3733 related, including the DC power injector,
crystals, and filters. He also sells dishes and complete setups.

As for making the most of your  current system, the first step is to hear the
MB, which is at 2401.323 + -  doppler. There is a good chance that the beacon
will be well off from where you expect it, my downconverter was off by about 130
Khz when I first installed it, and trimming was touchy at best.  I settled for
it being about 40 KC high and left it.

Scan up and down the band several hundred KC, you may find the beacon
where you don't expect it. You may want to see if it can hear a callibrated
local signal as well, such as a feed from a microwave signal generator.
Once you determine if your converter hears or not, you might want to play with
the position of the feed to determine the focal point of the dish.  A larger
dish would also help, a 1 meter dish will have 3x the surface area of a 0,6
meter dish.

As far as trying the bird when the satellite is near perigee, one problem with
that is that the antenna is usually pointing away from the earth. The satellite
controllers have maneuvered the antenna so it points toward earth when near
apogee, and the S-band antenna is of high gain. Another disadvantage of trying
to work AO-40 near perigee is that the doppler and the location of the satellite
change rapidly as it nears earth. Out near apogee, the location and doppler
change very slowly. which will give you time to zero in on the bird without
having to repoint the antennas and retune your radio constantly.

For your 435 Mhz uplink, you might want to consider a 12 turn helix antenna.
VE3ZAZ has a webpage describing it, and he has had good results with it. I am
using 2/3 of a KLM 40 element cross yagi, and 100 feet or so of (argh!) RG-214
to feed it. 100 watts on CW will almost always trip LEILA, and sometimes only 30
watts barefoot will as well. This is an AO-10 class antenna, so it is a bit of
overkill for AO-40.  A shorter feedline with better coax should give similar
results with only an 11 element yagi I figure, but I put the station together
with what I had laying around or could scrounge easily.

73,

Bruce N3LSY

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 :-(
>

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