Hi Jim,
Totally agree about the ideal location for the corcom filter from a text
book point of view but we have a solution that eliminates the RFI on 30
MHz at Mikes without having to mount the commercial filter to the neighbors
fridge, and don’t have to cut or coil the existing fridge power cord, etc.
On the other hand I have no problem asking the homeowner to fold up the
fridge power cord and plug it into a commercial filter that already comes
with outlet receptacles to see if that eliminates the need for the toroid
core choke in series with it.
Using a corcom filter in a stranger's home is asking for trouble from a
litigation standpoint even if it truly is not the root cause of problems
that might occur in the future (house fire, fridge failure, etc.). The
problem with the corcom and delta filters is that they are not plug and
play (electrical wiring into and out of the filter is involved since they
don't have built in power cord receptacles), and that’s why we are
searching for an off the shelf solution which we might have found for the
commercial power line filter per the APC product that Mike provided a link
for (we are looking into that). If it still needs to be used in tandem
with a toroid core choke that's something we will likely accept even though
not totally ideal.
Thanks for the additional recommendations on the toroid core choke for use
up on 30 MHz.
73,
Don wd8dsb
On Wed, Sep 29, 2021 at 10:46 PM Jim Brown <jim@audiosystemsgroup.com>
wrote:
> On 9/29/2021 5:04 PM, Don Kirk wrote:
> > Hi Jim,
> >
> > Looking at your published plots, it looks like there would not be much
> > difference on 10 meters between #43 and #31 material for the common mode
> > choke. Do you agree?
>
> No. I would stick with #31, and use the recommendations in the 2018
> Cookbook for TX chokes for comparable size cable as a starting point. If
> the problem is only on 10M, I'd try 4 turns through a clamp-on, paying
> careful attention to avoid crossovers. If the noise goes much lower,
> probably one more turn.
>
>
> > The case of the commercial filters were not mounted directly to the case
> > of the fridge, but the ground wire from the fridge power cord was
> > connected to the case of the commercial line filter, and the case of the
> > commercial filter then had a wire connected to it going out toward the
> > wall outlet ground via the power cord, so the ground wire from the
> > fridge was a continuous connection to the commercial filter case and
> > then from the commercial filter case to toward outlet ground. All power
> > cords used were 3 wire (line, neutral, and ground).
>
> What you did might be sufficient for LF, but we're talking 30MHz. That
> filter needs a VERY short bond to the chassis of the fridge that runs
> tightly with the AC cable from the fridge. If that's not done right,
> that wiring can radiate, because it forms a loop. When run tightly
> together, the conductors form a transmission line, and/or act as a
> single wire.
>
> Think of it this way -- done correctly, the Corcom (or Delta) bypasses
> phase and neutral to the chassis, like a feed-through cap, so the RF
> can't exit the box via the line cord. As one of my best my EE profs said
> it years ago for emphasis, "zero length leads."
>
> On 9/29/2021 4:09 PM, Gary Johnson wrote:
> > For best results, the Corcom filter should be bonded directly to the
> chassis of the offending equipment. That may mean cutting the cord very
> short, which we did on the UPS. Then the CM choke is placed on the cord
> right nearby. If these filters were in a nice external box with
> connectors on it, the long untreated power cord might still be enough of
> an antenna to radiate plenty of RFI.
>
> Agreed.
>
> 73, Jim K9YC
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