[Ham-Mac] TS-570 Digital Output and iMic Interface Issue

[Richard Kriss]

For Tom NU4G and others Mac users

I found the iMic interface problem and it is due to an impedance mismatch
with the digital audio output from the Kenwood TS-570D(G). Buried in the
find print on page 62 of the manual is note saying the digital output
(ACCY2, Pin 3 ANO) is 4.7 kohms. It is my understanding the industry
standard is 600 ohms for most rigs as well as the music industry.  The
specifications for the TS-570 output levels are not shown on the data sheet
or in the manual so I contacted Kenwood and they provided the following:

>Menu # 34 
>          Level 1 30 mVpp - 8 mV rms
>          Level 4 220 mVpp - 70 mV rms
>          Level 9 400 mVpp - 130 mV rms

The combined effects of lower than desired/expcted audio levels, an
impedance mismatch and using two interface devices resulted in what I was
calling attenuated audio.  The signal levels were too low to for the A to D
converters to recognize resulting in poor RTTY and BPSK decoding.

The Kenwood TS-570 cannot be fixed so I bypassed the iMic sending its
digital output to the SignaLink SL-1+ and in turn to the Line-in jack on the
rear of the Mac G4-450 AGP.  Yes, there is an impedance mismatch and loss
through the SL-1 but there is still signal to work with.  I tried several
tests and experiments and the iMic just does not work on the received side
due to the impedance mismatch issue.  I even tried bypassing the SignaLink
and using the TS-570's External speaker direct and via the iMic.  My current
setup is about as good as it gets.

I use the G4's Built-In Audio port for incoming signals and for outgoing
signals I use the iMic via one of the G4's USB ports. The reason for having
the iMic in line is because I have one and to maintain the system beeps. The
internal Mac sounds are muted if something is plugged into the headphone
jack. There are no interface or impedance mismatch problems on the transmit
side.

I use the SignaLink SL-1+ for two reasons. The cable provided with the unit
takes care of the interface to ACC2 port on the Kenwood and the SL-1's
unique  Auto-PTT circuit takes care of the transmit interface.  The Auto-PTT
works but requires a pretty strong audio signal for the SL-1 to trigger the
PTT line.

The interface problems I had may be unique to the Kenwood TS-570 and its
weird 4.7 kohm digital output. I understand most other rigs are 600 ohms so
the rest of you may be okay.

73 de Dick, AA5VU
aa5vu at arrl.net

Ps: My current setup may not be the best, but it is working very good with
the new soon to be released cocoaModem for OSX by W7AY and DarwinPSK by
DL1KSV. 


On 6/19/04 4:46 PM, "Tom Norris" <r390a at bellsouth.net> wrote:

> Dick, I use both and have for some time, I just plugged it all
> in and it worked. Have you adjusted the pots inside the SL-1
> to get max audio?
> 
> Tom NU4G
> 
>> I have been to digital hell and back this week trying to integrate new iMic
>> into my system. The 'problem' is on the Rx side.  I am getting the audio
>> from the TS-570's 13-Pin ACCY port and it goes to the SignaLink SL-1+ who in
>> turn passes it to the iMic for relay to the Mac G4's USB port.  The problem
>> is the combination of devices seems to attenuate the signal such that is
>> almost unusable for the software at the G4.
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