[Elecraft] Furnace RF Noise

[Jim Bolit]

Chuck,

Excellent point!

My design team in the Philippines did a variable speed power supply (4-6 kW
range) where we also had to design a simple common and differential mode AC
filter that was an available option if any "ham guys" (it was referred to as
the "ham guys" filter in our communications with the customer) raised a
noise issue with the power supply.  I only dealt with the power supply and
not the full system during the design process, but there were a number of
communications as it related to system radiated emi.

Jim
W6AIM


.



-----Original Message-----
From: Chuck Catledge [mailto:ae4cw at att.net] 
Sent: Monday, February 29, 2016 8:22 AM
To: 'Jim Bolit'; 'John K7JLT'; 'Mailman'
Subject: RE: [Elecraft] Furnace RF Noise

Jim,

The Corcom line filter may help (it did help "some" on my blower motor but
did virtually nothing for the condenser fan motor), but it does nothing to
prevent RF energy from escaping via the multiple control and sensor lines
that exit a typical furnace enclosure.  To prove that, I removed every
control and sensor line from the furnace enclosure and "hot-wired" the
internal control board to run the blower at full speed.  Thus isolated, the
RFI from the blower motor was completely contained and not visible on the
spectrum display nor audible on the radio.  So, the solution is that EVERY
wire that exits the furnace enclosure must by filtered or bypassed.  Since
all these lines carry low-voltage DC, a simple bypass capacitor on each line
will work.
---
Chuck, AE4CW
-----Original Message-----
From: Jim Bolit [mailto:jbollit at outlook.com]
Sent: Monday, February 29, 2016 10:28
To: 'Chuck Catledge' <ae4cw at att.net>; 'John K7JLT' <k7jltextra at gmail.com>;
'Mailman' <elecraft at mailman.qth.net>
Subject: RE: [Elecraft] Furnace RF Noise

Carrier air conditioning offers an add on filter IF the consumer complains.

The same may hold true for other appliance mfger's.

Why not just purchase a 20 amp Corcom metal can filter and install it with
the furnace.  I soldered the metal can of the filter to the inside of the
metal furnace housing.

Jim
W6AIM




-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Chuck
Catledge
Sent: Sunday, February 28, 2016 12:05 PM
To: 'John K7JLT'; 'Mailman'
Subject: Re: [Elecraft] Furnace RF Noise

John, beware of any furnaces (or ACs) with variable speed motors.  Some are
RF quiet; some are not.  There are three potential sources of RF leakage I
have personally experienced:
1) Variable speed inducer motor - this is a small motor used on higher
efficiency furnaces to provide draft air to the combustion changer.  Some
manufacturers have a kit that MAY reduce or eliminate the noise from this
motor.
2) Variable speed blower motor - this is the large motor used to move air
through the heat exchanger and into the duct system.  I have a 3/4 HP
variable speed motor in one system that is dead quiet; I also have a 1 HP
version of the same motor from the same motor manufacturer in another system
that is very noisy.  The engineer that designed the motor confirmed that in
the 1HP version it was difficult to manage RFI emissions.
3) Variable speed condenser fan motor - this is the motor on the outside
compressor/condenser unit.  Some manufacturers use a variable speed motor
running at a fixed speed for this application.  The one I have is very
noisy.

---
Chuck, AE4CW

-----Original Message-----
From: John K7JLT [mailto:k7jltextra at gmail.com]
Sent: Saturday, February 27, 2016 18:03
To: Mailman <elecraft at mailman.qth.net>
Subject: [Elecraft] Furnace RF Noise

I am blessed with a low noise level that matches my K3 and need to replace
my gas furnace without degrading my low noise level.  Has anyone out there
had any experience with a Ruud model U96V? Please excuse the off topic
subject.

John K7JLT

John K7JLT

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