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RE: Re: AO40Rcv and soundboards? ditto



Jim,
 I second that motion. I'm also in commercial broadcasting, and have hade
the same experiences. You hit it right on the head. I just grabbed an old
Radio Shack 10k-100k transformer and slapped in between the receiver and the
audio input to the soundcard. All hum gone!
73
Gunther Meisse
W8GSM
AMSAT LM:594


-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of Jim.Walls@sce.com
Sent: Wednesday, November 07, 2001 10:42 PM
To: amsat-bb@AMSAT.Org
Subject: Re: [amsat-bb] Re: AO40Rcv and soundboards?


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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