[RFI] Finally located my RFI

[Dave (NK7Z)]

Hi Dave (WO2X),

Thanks for the cross check here!!  Here is my rational-- the RFI starts 
at around 18 MHz, and ends at around 26 MHz.  Broadband noise...

Looking at the graphs for impedance on both mix31 and mix43, (I still 
need to check that I am correctly remembering the graphs), I see that at 
around 14 MHz., mix31. and mix43, are about equal in impedance, (apples 
to apples comparison, but for frequency), with mix43 having more 
impedance above 14 MHz., then mix31 does.  That dictated the choice. 
Had the RFI been centered lower, I would have selected mix31...

Now I am headed back to check the graphs to be sure my memory is 
correct!  If this is not a correct choice, I am all ears here...  I want 
to make this a one time trip to the next door neighbors home...

THANK YOU for your input on this as well...

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 06:55, Dave wrote:
> 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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