Re: [amsat-bb] Re: AO40Rcv and soundboards?

[Jim.Walls@xxxxxxx]

Moe - AE4JY said (in part):
> 4. 60/120Hz AC hum pickup can be a problem.  It may not show up on the
waterfall display since the display doesn't go that low but would screw up
the decoder.

I will second this one.  I have a background that includes working as a
broadcast engineer wherein my responsibility was a studio for a major radio
traffic reporting service.  The biggest source of hum and noise problems I
had to deal with was unbalanced audio lines.  Either a balanced device
connected to an unbalanced device or two unbalanced devices connect
together.  The solution was very simple.  Anything that was not a true
balanced device was run through an isolation transformer before being
connected to ANYTHING else.  Almost all the noise, hum, and crosstalk
problems went away.

When I started using AO40RCV to decode telemetry at home, I had a low
percentage to good CRCs.  As soon as I put isolation transformers beween
the PCR-1000 receiver (unbalanced) and my Mackie sound mixer (balanced) and
from the Mackie to the sound card in my PC (unbalanced), I got almost 100%
good CRCs - except when the neighbor with the 2.4 GHz cordless phone
splatters all over the AO-40 downlink.  In case you are wondering, a direct
cable from the PCR-1000 to the sound card (bypassing the Mackie) was no
better than going through the mixer without the isolation transformers.

In other words, I highly recommend an audio isolation transformer between
your receiver and sound card.  If someone want the details of the
transformer I used, just ask.  I'm at work and don't have the part number
with me.

73
-----------------------
Jim Walls - K6CCC
k6ccc@amsat.org
Mobile Radio Operations
Southern California Edison Co.
Ofc:   626-302-8515   -   PAX   28-515
FAX:   626-302-7501   -   PAX   27-501


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