[Ham-Mac] CI-V interface noise

[Chris Smolinski]

It is possible that you're getting some radiated RFI on the USB 
cables, which is then getting picked up by your antenna. If that is 
the case, then no amount of filtering in the interface is going to 
help, since that isn't the path the RFI is taking.

You might be getting RFI pickup on your incoming antenna line, as 
well. I assume you're using good quality coax. Improving the ground 
to your radio may of course also help.

I can't speak for the MicroHam interface, but I put an LC filter on 
both the ground and data lines on the CI-V side of my interface, the 
cutoff freq is 150 kHz or so (you can't go much lower or you start to 
corrupt the serial data stream).

>This is driving me bonkers.  There has got to be someone else on 
>this list with this problem besides me.
>
>Problem:  When I connect my iMac to my Icom 746pro (USB from 
>computer to "data" port on radio), I get a LOT of noise appear in 
>the radio.
>
>Equipment:  PowerPC iMac, running Tiger.  MicroHam USB interface II.  
>Icom 746pro.  I use MacLoggerDX and CocoaModem.
>
>Specifics:  Click the "Radio VFO" box on MLDX, and the noise 
>appears. Click it again and the noise goes away.  It is worst 
>(unacceptable) on 15 meters;  also present on 20m and 17m.   Before 
>I went to my current interface (MicroHam) I was using a Black Cat 
>USB Ci-V interface with the same problem, but it wasn't as noisy as 
>my current interface.  I mostly solved the problem before by 
>wrapping the USB cable from the computer through a large toroid. 
>(transformer E core, to be precise.)  When I put the MicroHam 
>interface on, I put an additional E core on the cable, and still 
>can't reduce the noise to what I consider acceptable levels.  I've 
>tried grounding the iMac, grounding the interface, etc. to no avail. 
>(Where the heck are you supposed to ground an iMac anyways? I pulled 
>the back cover off and attached a braid to a case screw.)   I am 
>annoyed that using interfaces with supposed "isolation" still 
>doesn't eliminate the noise.  Anyone have any suggestions for 
>something I haven't already tried?
>
>Thanks in advance,
>
>Chris
>KF7P
>
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Chris Smolinski
Black Cat Systems
http://www.blackcatsystems.com