> On Jan 15, 2017, at 9:56 AM, Tim Shoppa <tshoppa@gmail.com> wrote:
>
> Also... this may sound stupid... but make sure you are actually feeding the
> decoder off of "line in" and not off of a microphone that may be plugged
> into the PC.
This probably happens more often than you think :-).
I have many times received email that cocoaModem was not decoding well even
with clean loud signals. I tell them to make sure the sound interface is
selected for line-input rather than computer microphone (many Macs come with
built in microphones), and usually get an "oops" reply.
When sound card levels are set up properly, a computer microphone that is place
at the receiver's speakers can work surprisingly well. However, if the
microphone is more than a foot from the speaker, the room noise (fans,
keyboard, dogs and children, etc) starts to become a factor (think S/N ratio).
A microphone that is further away from the speakers can also generate multipath
from sound that reflects off other objects and the walls of the room. An RTTY
symbol of 22ms is equivalent to the time it takes sound to travel about 25
feet. If the distance from the speaker the wall and then back to the
microphone is more than 10 feet, the modem receives the equivalent of
moderately severe multipath :-).
Just turn off the volume from the speakers, and if the RTTY decoder also stops
decoding, it is likely that you are receiving through a microphone instead of
the line-input.
73
Chen, W7AY
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