[RFI] Finally located my RFI

[Dave]

Curious why you would choose mix 43 over 31 for HF interference? Is there a specific advantage in this situation? I thought 43 were more effective at higher frequencies. 

73
Dave wo2x
Sent from my waxed string and tin cans. 

> On Jun 20, 2024, at 8:26 AM, Dave (NK7Z) <dave at nk7z.net> wrote:
> 
> Hi Jim,
> Thanks for the reply, and suggestions...  I have six mix43 FT240s in stock now...  I also have a pile of mix31s, but in this case, I think the 43s will be better...
> 
> Can either you, or Dave (W0LEV),  suggest a commercial unit that can be purchased, that I can have an electrician install?
> 
> If it were my unit, I would install however, being a neighbors unit, I want an electrician to install due to liability issues.  I am fairly sure I can get the HVAC folks to wrap a 43 core on the control lines at both ends...
> 
> 73, and thanks,
> Dave (NK7Z)
> https://www.nk7z.net
> ARRL Volunteer Examiner
> ARRL Technical Specialist, RFI
> ARRL Asst. Director, NW Division, Technical Resources
> 
>> On 6/20/24 00:01, Jim Brown wrote:
>>> On 6/19/2024 6:08 PM, David Eckhardt wrote:
>>> Dave, install ferrites on BOTH the input AND output.
>> I think you mean on both the mains power side and the control lines. Strongly agree. BUT -- it's going to take more than single-turn clamps that peak around 140 MHz to make much of dent between 17 and 29 MHz.
>> Couple of thoughts. First, dedicated twisted pair for the current carrying conductors.
>> Second, look for anything that would divide some of the return current with a random ground path, like building structure. The logic -- when forward and return current can form a transmission line, their fields cancel as long as they're equal, (and are confined to the narrow region between the conductors that make up the line), AND the transmission line is a much lower impedance than the wider random path, so all the current goes to it. But if their is no transmission line, the return current in that random path creates a large magnetic field, and also radiates as an antenna.
>> Henry Ott got me to see this light years ago, and I got the same analysis with an EMC engineer I encountered when he showed up as a friend of the client at a church in Dayton for which I was designing a sound system. The first thing he said after I'd outlined the issue was "twisted pair."
>> 73, Jim K9YC
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