[RFI] Request for Comment (Rheem RP1748 A/C System)

Jim Brown jim at audiosystemsgroup.com
Mon Nov 9 20:12:29 EST 2020

On 11/9/2020 4:22 PM, Steve Dyer W1SRD via RFI wrote:
> Does the shielding help prevent RF getting *into* the cable?
> With these new 4 wire HVAC control systems I worry about RF getting in 
> the system too.

Hi Steve,

In my experience, common mode is the primary issue at HF, and probably 
at VHF. I say that because a clamp-on ferrite has long been the weapon 
of choice to satisfy compliance testing, which only happens at VHF and 
above, and wound ferrite chokes usually solve it at HF. My educated 
guess is that Pin One problems inside the gear are what couples common 
mode into and out of the equipment. The simple clamp-ons used by 
compliance engineers are also common mode chokes, simply optimized to 
place the resonance at VHF.

73, Jim K9YC

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