[RFI] update <was> 40m (and other) noise

Eric - VE3GSI ve3gsi at sympatico.ca
Sat Apr 11 19:31:02 PDT 2009

Come on Guys,

I only suggest the little Belkin cube as a line filter, if only for
convenience. NOT for the surge protection!!!! The little one I have, model
F5C594 has been replaced here:


Check the features, EMI/RFI up to 43 dB. I sort of recall that is at 100 MHz
so attenuation may not be enough for lower frequencies. I sort of recall
another model is bit more aggressive so anyone looking may wish to check
other cubes.

I am sure someone with a solder gun and pile of parts can make something
that most likely will do a better job. But the fellow's neighbour with the
noisy cell phone charger may not want a home brew box hanging off the wall.
Like I said in my original post, I have had some success with minor noise
problems, including a Dynmax battery charger and our new fang-dangled
washing machine.

Heck if it works, all be it good. If not take it back to the store and get
your $.$$ back, after all Home Depot do have a no questions ask return
policy. <grin>

Happy Easter all, and may Bugs Bunny bring you lots of chocolate.

Eric - VE3GSI


> -----Original Message-----
> From: Roger (K8RI)
> Sent: April-11-09 8:47 PM
> Cc: rfi at contesting.com
> Subject: Re: [RFI] update <was> 40m (and other) noise
> Eric - VE3GSI wrote:
> > Hi Jim,
> >
> > I'll check your info out first chance I get. But..... in my years of
> > servicing I have seen MOV built into many AC circuits of home
> electronic
> > equipment. In fact years ago, I remember one company (Zenith)
> requesting
> > them to be installed after repeated failure of one model of their TV
> that
> > failed even if it seen lightning on the horizon, the MOV fixed that
> problem.
> > Are MOVs not common place with just about all quality switching
> supplies
> > these days?
> >
> MOVs are the equivalent of a clipping diode and protect from spikes.
> They do little if anything for filter out noise and I've never head of
> them being used for that purpose. They are often used to protect
> inexpensive power supplies or those sensitive to power line spikes. I
> would expect them to become noise generators rather than suppressors.
> The Metal Oxide Varistor (MOV) is a whole batch of metal oxide diodes,
> physically compacted to form a disk.  There is a threshold voltage at
> which conduction begins, but unlike a Zener diode the threshold is just
> that, a place where conduction begins and increases as voltage
> increases
> to a point where the device basically becomes a short circuit.  Each
> time an MOV conducts it loses a few of those little diodes so the
> performance and threshold degrade over time with use.  They may fail
> shorted or open depending on conditions. A large spike can literally
> leave nothing but a pair of leads.  Lots of little spikes will
> eventually cause the diode to short. If the circuit has insufficient
> protection it too will end up as a pair of leads.
> MOVs are generally rated at threshold conduction in volts and jouls of
> capacity.  When used in an AC circuit you have to keep the threshold
> *above* the peak voltage. IOW, multiply RMS by 1.414 and then add a bit
> of head room or the device will have a very short life.
> The larger MOVs with capacities of 50,000 jouls or more can fail
> spectacularly.  It's even more spectacular if you are only a few feet
> away.
> Yes, IIRC nearly all the computer power supplies I've taken apart had
> MOVs across the AC line for protection.
> 73
> Roger (K8RI)
> > But with the fellow that has the noisy neighbour these little filters
> might
> > be just what he needs for the charger in question. I have seen
> reduced noise
> > with the Belkin units with RFI ratings (not the generic models). On
> one of
> > my own Dynamax chargers I have seen noise from it reduced to a
> liveable
> > level, until I had a chance to replace it with a better quality one.
> >
> > Besides I can't see Belkin setting out to blow up everybody's home
> theatre
> > system and computer.
> >
> > I will check your article,
> > Eric - VE3GSI
> >
> >
> >
> >
> >> -----Original Message-----
> >> From: Jim Brown
> >> Sent: April-11-09 6:06 PM
> >> To: rfi at contesting.com
> >> Subject: Re: [RFI] update <was> 40m (and other) noise
> >>
> >> On Sat, 11 Apr 2009 17:44:22 -0400, Eric - VE3GSI wrote:
> >>
> >>
> >>> The ones I use are by Belkin
> >>> called and 'Surge Master' available at Home Depot here in Canada.
> >>>
> >> Note that I do NOT recommend MOV surge suppression products, which
> >> is what these devices are. MOVs can be really bad news on branch
> >> circuits, because they can actually CAUSE destructive failures of
> >> interconnected equipment. The only good application for them is as
> >> part of a "whole house" suppression system installed at the service
> >> entrance.  For a technical discussion of this, see the Power and
> >> Groudning tutorial or the RFI tutorial on my website.
> >>
> >> 73,
> >>
> >> Jim Brown K9YC
> >>
> >>
> >

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