[amsat-bb] CAREFULL suplying your AIDC3733 converter!

[fredf@xxxxxxx]

Hi all,


The AIDC 3733 converter can NOT be powered with 12-13Vdc,
or whith the "preamp" supply of a transceiver,without a 
previous modification:
the voltage is internally regulated with a 7812 regulator.
Such regulator have a voltage drop of about 1.5-2 volts,
the resulting voltage will be inaceptable for the 3733 to 
work properly.

I began to make experiments whith the diode Signal 
Generator on 50mhz,and the FT847 supplying directly the 
3733 via the coax.
I noticed on 123.1 mhz a strong noise ,but not at all the 
clear signal expected.
Then i measured the voltage at the F connector of the 
converter, it was about 11,5V , because of the loss in 
the coax cable (only a few meters).
At the imput of the 7812 regulator(inside the 3733),it 
was somewhere around 11.0 V,(loses in the coils) and at 
the output 9,6 V.
Desoldering the coil at the input and suplying 13 V 
directly bring back to life the converter,with a clean 
signal, but the voltage on the output of the 7812 
regulator was still around 10.6V, and consequently, not 
regulated.
I connected it on my spectrum analyser, (it suplies the 
converter via the coax), and the signal was nice but with 
a fast and quick (small) oscillation. 
This oscillation did not *aparently* degrade the 
reception quality,the sound from the SG seemed clean.
I then suplied the 3733 with 18V and the signal becomes 
about 40% stronger,NF improved a lot and it stopped 
oscillating.

here are some solutions for this problem:

-Supply it with 15-18V via a bias tee.Probably the best.
-remove the 7812 regulator and short in an out pins
(the supply will not be regulated any more, that may 
increase the drift,it depends of the quality of your 
power supply.)
This way, you can try to use the "preamp" power suply of 
your transceiver,but be carefull with the (DC) loss in 
the cable.Check the voltage in the 3733 with the lenght 
of cable that you will use.(at the output of the 
7812.Should be 11.9 V)
-Make a hole in the cover or side of your converter,fit a 
feed thru capacitor,short the in/out of the 7812 
regulator and supply it separately with 13V.


I hope that will help.I had to remove my DEM transverter 
because the "weatherproof" box i made stopped its mains 
function (yes,stopping water),and instead to repair it i 
consider to try the AIDC converter.The specifications 
seems better anyway.
I have fixed the 3733 directly to the feed,soldering the 
31,5 mm probe directly to it.
I hope today i will be able to get telemetry again.

 

Hoping that will help,

Best 73 and good luck.

Fred, CU8AO
Flores Island.



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