[Elecraft] RFI in audio chain

[John Kramer]

Jan

The easiest, quickest and cheapest method is to wind yourself an “ugly balun” in your coax cable line. 
It must be located OUTSIDE your shack to choke the common mode currents from entering the shack.
Wind about 15 - 20 turns of your coax on a 6” PVC pipe. This will give you about 2500 ohms choking
impedance. 

If there is still RFI getting in the shack, then purchase a commercial choke either from
http://www.balundesigns.com/model-1115d-max-choking-1-1-balun-1-54-mhz-5kw/  
this will provide about 10 - 12 000 ohms of choking impedance, or buy one from

http://myantennas.com/wp/product/cmc-130-3k/
This one will give from 12 000 - 15 000 ohms of choking impedance.

These common mode chokes merely get plugged inline in your coax cable. Always better to locate
them outside the shack

73
John




On 23 Nov 2015, at 1:02 AM, Jan Ditzian <ditzian at windstream.net> wrote:

I have a problem that appears to be changing, but I could use some help.  The problem is RFI in the audio input (microphone input) when I use my vertical antenna on 40 meters.  Here is a rundown of what has happened:

I have a 67-foot elevated vertical that I can use on 80 and 40, and it works fine on CW.  However, on SSB, both bands, there clearly is feedback; there is no feedback on the other bands where I use a C3 yagi.  Initially, the feedback was so bad that the rig would go into oscillation, and I had to turn the amp to standby.

I recently purchased the new KSYN3A and decided to install it.  I replaced the K3 with my IC-730 backup, using the hand microphone that came with the 730.  The 730 did not have any RFI.  I finished the modification and returned the K3 as the operating rig.  Now, the RFI on 40 seems to have diminished substantially or disappeared, but it still happens on 75/80.  However, it seems to be much less there as well.  I do not suspect that the KSYN3A had anything to do with this, but perhaps I tightened connections better when I returned the rig to service.  I also redid some ground connections.

The microphone for the K3 is an Audio-Technica that works well everywhere else.  It has a long cord, though.  I put a few toroids on the cord near the microphone connector and that has possibly reduced RFI a little, but it is still there.

Is there a possibility that a bypass capacitor is bad, or has someone else had the problem and solved it externally to the K3? For instance, has anyone found that a long string of ferrite beads has cured this problem?

Despite decades of operating, I am hardly a troubleshooting hotshot, and I would appreciate guidance.

Thank you,

Jan, KX2A


______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to jkramer at iafrica.com