[1000mp] Sound Card - FT1000MP

[Joe Subich, K4IK]

> 	Simple solution is to attenuate the signal, Radio Shack 
> sells a 60 dB. attenuating audio cable for about $3, no 
> soldering required. An isolating transformer helps clean 
> up the HUM especially if you have the speech processor 
> turned on.

Using an attenuator between the sound card and the patch 
input is absolutely the wrong thing to do:  

   1) the patch input is at mic level.  Use the DVS input 
      for voice ... it bypasses the mic preamps and requires 
      a more appropriate level. 
   2) Do not attenuate the line out of a typical sound card, 
      turn down the sound volume.  The line out amplifiers 
      in most sound cards do not have sufficient headroom 
      to handle full output without distortion (IMD).  Run 
      the "Playback" and "Wave/MP3" level sliders at no more 
      than 50%.    

An (high quality) audio isolation transformer is a good idea 
to help eliminate hum (ground loops).  However, make sure it 
is of high quality and does not saturate the core in the 
presence of RF or you will end up with distortion problems.  

Further, using an attenuator ahead of the patch input is 
a good prescription for RF feedback problems.  The patch 
input has two high gain stages ahead of the gain control. 
Any RF feedback on the low levee audio will be much harder 
to resolve on the patch input.  


73, 

   ... Joe, K4IK