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

Wed Feb 12 07:07:18 UTC 2014

Good point. And if you were to lose the ground between your radio and its power supply the radio would try to find its high current ground through the URI back through the computer power ground. In any event bad things could happen. I will have to put a ground between the radio and computer.
73 Doug
WA3DSP
http://www.crompton.com/hamradio

To: app_rpt-users at ohnosec.org; ars.w5omr at gmail.com
From: ke2n at cs.com
Date: Tue, 11 Feb 2014 17:26:59 -0500
Subject: Re: [App_rpt-users] App_rpt-users Digest, Vol 60, Issue 39

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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