[App_rpt-users] App_rpt-users Digest, Vol 60, Issue 39

[Ken]

My understanding is that  a USB port looks for the voltage dip caused by connecting your device - USB devices are supposed to have a capacitor on the +5 line just to cause a surge of current on connection.  If you re-plug before it discharges, the port probably will not initialize properly.

The other issue with the URI is that it basically connects the DC ground of the computer through to the DC ground of the radio.  There are some 600 nH chokes that don't do much of anything below VHF frequencies.  With one setup, I had an audio hum problem caused by ground loop currents. Connecting a short, direct, #10 wire between the radio chassis and the computer chassis neatly fixed this.  It might help a bit with HF RFI too, possibly in addition to the ferrites on the other cables. The RF would still flow, but not through the URI.

73
Ken


 
	
Attached Message
	
		
			
From:
			
Geoff <ars.w5omr at gmail.com>
		
		
			
To:
			
app_rpt-users at ohnosec.org
		
		
			
Subject:
			
Re: [App_rpt-users] Loosing TX
		
		
			
Date:
			
Mon, 10 Feb 2014 12:03:20 -0600
		
	

          
    
    
On 02/10/2014 08:34 PM, Doug Crompton      wrote:
    
    
            
Another thing to          consider on the DMK is RFI. They are very susceptible to it          especially higher power HF but be aware that any RF could          cause problems. I have had this happen at two different          locations. The fix was ferrites on the leads in and out. One          on each lead worked for me but more may be necessary depending          on the severity. You can also wrap multiple turns through a          single ferrite if they fit. 
          
          This shows up a a locked interface and usb error messages that          in my case specifically said EMI? It might not always catch          that it is an EMI problem though so other errors might          indicate the same thing.
          
          Since the DMK is nothing more than a fancy USB sound FOB I          suspect any FOB might have this problem. Lead length both          audio and USB would also be a factor.   
      
    
    
    Agreed.  
    
    I am curious, though, what voltage is sent back to the USB buss from    the device.
    My reasoning is, that in -my- case, when this happened, I noticed    that if I pulled the USB cord, let it set for 15 or 20 seconds, then    plugged it back in, the green light lit up, and as soon as it    Transmitted, that URI died, again.  Shutting down the machine, to    the point of letting the caps discharge, etc, then bringing    everything back up, plugged in, all worked flawlessly...
    
    until, at least, I RF'ed the system again with HF signals from 75    and/or 40m.... ~sigh~
    
    73 = Best Regards,
    -Geoff/W5OMR
    
  

 


 
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