[Elecraft] RFI in audio chain

[Vic Rosenthal]

I don't like 'ugly baluns', especially for the lower bands. If you do use one, you should wind the coax as a single layer solenoid, not a "hank" of coax. Also, as someone else suggested, you need a large number of turns for it to be effective on 80 m.

Vic 4X6GP/K2VCO

> On 23 Nov 2015, at 2:32 AM, Jan Ditzian <ditzian at windstream.net> wrote:
> 
> 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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