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 <[email protected]> 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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