[ICOM] Simple digital interface question

[Stephen Budensiek]

John,
   Not sure what mode you're trying to work.  I assume RTTY or PSK31 or similar.
   You will need 2 cables, one from the audio out on your 706 to the
mic in or line in on your sound card for it to hear the signals.   You
will need a second audio line from the line out on your sound card to
the mic, or the back connector audio input on the 706.   There will be
3 issue's you need to resolve.  Doing that very easily generates hum
from RFI on your transmit audio.  Makes a wide, nasty signal on the
air.  I recomend have a clip on Ferrite at both the radio end, and the
sound card end.  I also put a .001 disc cap on the audio line right at
the mic plug, to also help decouple any RFI or RF hum on transmit.
Another issue you will need to deal with are input/output audio
levels.   If your sound card output is speaker level, it will be hard
to control audio into the mic, you will have to turn it almost totally
all the way down.   I typically put a 10k ohm resistor  in series with
the incoming audio, and a 1kohm resistor to ground (on the mic side of
the 10k), which gives you a nice transmit level, helps aleviate any
hum from RF, and the such.   It makes it nice if you go to the back
connector to get your receive audio to the sound card, you don't have
to play with the volume control when you go from digital modes to the
microphone on the air.   I've just built a cable for a new setup a
month ago, started out with cables to mic/ headphone out on the radio,
and the audio in/out on the sound card.   There was only 20 ft from
the vertical on my camper to the radio, so the RF ate it up till I did
the RFI bypassing.

73's de Stephen, K0SD in TX

*******************************************

On Tue, Jan 4, 2011 at 12:17 PM, John Geiger <aa5jg at fidmail.com> wrote:
> I am looking for a cheap/simple way to interface an Icom 706 series radio.
> Will running a cable between the line out jack on a soundcard and the mic
> jack on the 706, and then using VOX on the 706, produce acceptable audio?
> Or is a more complicated interface needed?
>
> 73s John AA5JG
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