Re: IC700 and PRO7 IC headset RFI on my rig

Steve W3AHL

I would start with adding a common-mode choke on the output of the AH-4 instead of at the feed point.  A coiled coax (solenoid) choke provides minimal CM attenutation across the bands due to capacitive coupling between the turns.  Eight turns of RG-8X wound as a single layer on 6" PVC pipe (best case for your situation probably) results in about 760 ohms at 7 MHz, peaking at 15,000 ohms at 12 MHz and back 2800 at 14 MHz, 860 at 21 MHz and 360 at 28 MHz.  The capacitance results in self-resonance that causes actual performance to vary greatly with minor changes in construction details.

The goal should be 3,000-5,000 ohms across all bands.  This is achievable using 5 turns of RG-8X through 5 type 31 2.4" ferrite cores (Fair-Rite part # 2631803802, about $6 USD each ), taking care to splay the turns of coax out to minimize capacitive coupling.  This provides 4,500 ohms at 7 MHz, peaking at 5,500 at 14 MHz and down to 3,000 at 28 MHz.  Performance is much less affected by minor variations in construction, as long as the turns for coax are spread out and secured so they stay that way.

For good practical info on RFI backed up by measurements and lots of experience see:   K9YC has many other good articles on his web site.

Steve, W3AHL
---In ic7000@..., <colin.christie34@...> wrote :

Hi Steve,

 the test of the headset/microphone was done at my friends place. It worked fine with the IC7000.

 I doubt my radio has any problems. 
Going to relocate the AH4 outside the shack and connect up again to see if RFI is still present.

My other thought is to make a coax choke of 8 turns and placed it under the balun before the coax transmission line and see what happens.


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