[Elecraft] KX3 I/Q to soundcard isolation

[Jim Brown]

On 10/15/2012 9:10 AM, N6363LLL wrote:
> There are big differences between interfacing a PC to the KX3 I/Q port
> compared to the needs of digital modes that use the headphone and mic audio
> connections.  The I/Q port requires a flat bandpass to at least 48Khz.

The noise some are experiencing sounds like a Pin One Problem in the 
computer, the rig, or both. Two cures, use both, but do #1 first, 
because it's simpler and cheaper.  NO TRANSFORMER IS REQUIRED.

1) Bond from the chassis of the computer/sound card to the chassis of 
the rig with short fat copper.  For more on this see 
http://audiosystemsgroup.com/HamInterfacing.pdf

2) Use a serious multi-turn ferrite choke on the audio cable, using the 
measured data in Appendix Oneof http://audiosystemsgroup.com/RFI-Ham.pdf 
as a guide.  Use Fair-Rite #31 or #43, depending the bands where you are 
hearing noise.  Put the choke on the audio cable(s), NOT on the bonding 
wire.

3) Another important point.  High futility cables often have lousy 
shields (and often no shield at all, only a wire connecting the shield 
contacts). I build my own audio cables using RG58 or RG174 and audio 
connectors that I buy from Full Compass in Madison, WI. See the 
above-cited references for part numbers.

73, Jim K9YC