[Ham-Mac] Re: [Ham Mac] Sound Card

[Chris Smolinski]

>I have followed the lengthy discussion on what is basically an audio 
>problem, complicated, so it seems, by impedance matching.
>Whilst I have no experience of the iMic or the TS-850, in all the 
>discussion I have not seen the word 'Oscilloscope' mentioned.
>
>Surely a basic oscilloscope would give some insight into transfer 
>voltages in whatever system is being used.  No ham should be without 
>one - hi!

Agreed. I actually mentioned my use of a scope in the iMic tests I 
did on Tuesday, which curiously seems to have been 
overlooked/ignored. It clearly shows that there is no "impedance 
mismatch" problem between the iMic and a radio with a 4.7k ohm output 
impedance capable of causing the described symptoms. The situation is 
certainly not comparable to "SWR" either, since, sorry to repeat 
myself yet again, we are not dealing with the case of trying to get 
maximum power transfer. For all practical purposes, computer audio 
input devices are voltage sensors. A low digitized audio level can 
only be caused by a low input voltage level.

BTW, 5 minutes of poking around the web found a copy of the 570 
manual, which indicates that 'setup menu 34' sets the output level of 
the ACC2 ANO audio output. This might be relevant.

The obvious solution here is to get out a scope and possibly function 
generator, and take some measurements, to determine what is 
happening. The first measurement to make is the actual voltage level 
of the radio's audio output (the signal being used) unloaded. Then 
connect the iMic and repeat the measurement. Also, be sure to run 
some software on the Mac that is capable of accurately displaying 
what the input audio level is. Once this is done, the measurements 
will most likely shed light on what the actual problem is. I agree 
this is not as much fun as pure speculation, as the ancient Greek 
philosophers were accustomed to doing, but it might actually produce 
a valid answer, and suggest a solution.


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Chris Smolinski
Black Cat Systems
http://www.blackcatsystems.com