[Elecraft] RFI in audio chain

[Jan Ditzian]

In response to the balun recommendation from several hams, I apologize 
for forgetting to mention that the vertical has an "ugly balun" both at 
the antenna and near where the feedline enters the house.

Part of the reason I put the question to this group, after first 
thinking that the amps group could help, was the fact that the IC-730 
shows no RFI, while the K3 shows extreme RFI.

Thanks,

Jan, KX2A

On 11/22/2015 6:36 PM, John Kramer wrote:
> 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
>
>
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