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Richard Stouffer · 12-05-2007, 06:27 AM

Here's the response I recieved from the Doctor at ARRL. It's a bit on the general side, but it does provide some other possibilities to pursue.
By the way, I've been very impressed at the responsiveness of the Doctor. I've gotten a response to every inquiry and often within a day of asking, even on weekends.

Richard,

I am not familiar with GFCI in a motor home but assume they are the same as a conventional home. If so, one solution to your RFI problem might be to replace your GFCI outlets with a different brand. We've had favorable reports with Leviton GFCI outlets, which are available in both 15 and 20 amp versions for 117 VAC. They are readily available at Home Depot and Lowes home centers, and probably most others. Bryant Ground Fault receptacles also features a published 0.5 volt immunity from 150 kHz to 230 MHz. We have received good reports concerning their imunity effectivness from other amateurs. Online Information is available from Bryant at: http://www.hubbell-bryant.com/pdfs/BSS100.pdf.

Another possible cure might be a filter between the GFCI and power cable. There are commercially available "brute-force" AC line filters, but installing one is another matter. If the maximum load at the GFCI outlet is less than 300 watts (about 2.5 A), a Radio Shack catalog #15-1111 might work. (Note: This is unlikely if you use a toaster at this outlet) If not, some of the filters sold by Industrial Communications Engineers, http://www.arrl.org/cgi-bin/tisfind?...ndustrial+Comm should do the trick.

It may not be possible to add such a filter due to space limitations in the GFCI area. One possible cure in this case is a ferrite bead on each lead right at the GFCI. The bead need only be just big enough for the wire. Be sure to select a ferrite mix that is suitable for the frequency of interest. Several beads might provide increased immunity, especially in the case of HF.

A common mode choke on the cable leading up to the GFCI is another similar but possible cure. While the ARRL RFI Book contains a detailed explanation of the common-mode choke, you'll find making one is a pretty simple matter. Wrap several turns (as many as you can get) of the power cable onto an FT-240-73 ferrite core.) The common-mode choke should be installed right at (or near) the affected GFCI. In addition, you could try several chokes along the cable leading up to the GFCI. This will hopefully break up any resonant lengths along the cable, something which may cause one GFCI to trip while the others remain unaffected.

The ARRL "RFI Web Site" contains a list of EMI/RFI materials suppliers for ferrite chokes. You can also refer to the advertisements in QST -- there are a few advertisers offering ferrite materials and chokes.

73,

Mike Gruber, W1MG

12-05-2007, 06:27 AM	#12
Richard Stouffer Senior Member Join Date: Nov 2007 Posts: 188	The "Doctor's" Opinion Here's the response I recieved from the Doctor at ARRL. It's a bit on the general side, but it does provide some other possibilities to pursue. By the way, I've been very impressed at the responsiveness of the Doctor. I've gotten a response to every inquiry and often within a day of asking, even on weekends. Richard, I am not familiar with GFCI in a motor home but assume they are the same as a conventional home. If so, one solution to your RFI problem might be to replace your GFCI outlets with a different brand. We've had favorable reports with Leviton GFCI outlets, which are available in both 15 and 20 amp versions for 117 VAC. They are readily available at Home Depot and Lowes home centers, and probably most others. Bryant Ground Fault receptacles also features a published 0.5 volt immunity from 150 kHz to 230 MHz. We have received good reports concerning their imunity effectivness from other amateurs. Online Information is available from Bryant at: http://www.hubbell-bryant.com/pdfs/BSS100.pdf. Another possible cure might be a filter between the GFCI and power cable. There are commercially available "brute-force" AC line filters, but installing one is another matter. If the maximum load at the GFCI outlet is less than 300 watts (about 2.5 A), a Radio Shack catalog #15-1111 might work. (Note: This is unlikely if you use a toaster at this outlet) If not, some of the filters sold by Industrial Communications Engineers, http://www.arrl.org/cgi-bin/tisfind?...ndustrial+Comm should do the trick. It may not be possible to add such a filter due to space limitations in the GFCI area. One possible cure in this case is a ferrite bead on each lead right at the GFCI. The bead need only be just big enough for the wire. Be sure to select a ferrite mix that is suitable for the frequency of interest. Several beads might provide increased immunity, especially in the case of HF. A common mode choke on the cable leading up to the GFCI is another similar but possible cure. While the ARRL RFI Book contains a detailed explanation of the common-mode choke, you'll find making one is a pretty simple matter. Wrap several turns (as many as you can get) of the power cable onto an FT-240-73 ferrite core.) The common-mode choke should be installed right at (or near) the affected GFCI. In addition, you could try several chokes along the cable leading up to the GFCI. This will hopefully break up any resonant lengths along the cable, something which may cause one GFCI to trip while the others remain unaffected. The ARRL "RFI Web Site" contains a list of EMI/RFI materials suppliers for ferrite chokes. You can also refer to the advertisements in QST -- there are a few advertisers offering ferrite materials and chokes. 73, Mike Gruber, W1MG