Mark wrote:
Dave wrote:
Mark wrote:
modelman wrote:

Several months ago I had a high efficiency Trane XV90 natural gas
furnace and heat pump installed. Since the weather has recently been
cold enough for the gas furnace to provide heat, I have been
experiencing severe radio interference. The interference wipes out AM
broadcast reception throughout my house. I also see snow on a TV
connected to an external antenna.

The radio noise occurs as soon as the draft inducer motor starts up;
the pitch of the interference is related to the motor speed. The draft
inducer motor is a dc motor driven by a PWM controller on the main
circuit board. ... SNIPPED ...

DC motors are notorious noise generators. Those of us who used to be mobile when
6 VDC was the value of a car battery, and alternators did not exist, will attest
to the facts of generator [DC motor] noise.

A DC motor uses brushes to contact windings within the motor. As the motor turns
the brushes continually make and break current in the rotating armature
[inductance]. This making and breaking creates a very wide HF and lower VHF
noise spectrum. [Lots of sparks].

The solution, in the olden days, was a coaxial capacitor mounted directly to the
frame of the motor with the DC power running through the capacitor. I recall the
capacitor was about 1 inch in diameter and 2 inches long. Sprague made such a
critter.

Hope this history helps.

/s/ DD, W1MCE

I'm pretty sure these motors don't have brushes and are electronically
commutated and the electronics are causing the EMI...
Mark

Hi Mark, Modern HVAC, dishwashers, washing machines,ect. use variable
speed drives, which increases the efficiency of the devices. The
increased efficiency produces increased RFI due to the switching action
of the solid state devices (SCR's, BJT's, IGBJT's.ect). My washing
machine drives me crazy on Sat. morning on HF as my maid does the
weekly wash. As for what you can do? I don't know, it would require
vast amounts of filtering at the drives, I am sure that Trane and
other mfgrs are not willing invest in.

This is completely different from the usual thermostat interference,
and will be much more difficult to get rid of.
Gary N4AST

Interesting discussion, folks....

As a controls engineer and High-Voltage electrician.... as well as
delving into HVAC control of late... here's my observations...

These manufacturers will always take the cheapest route possible and
damn the consequences. This is particularly true in power and control
systems.

A whole lot of manufacturers are moving toward PWM drives on their
blowers in particular. Many solutions are an 'on-board' frequency
chopper that is integral with the blower's motor.

These choppers are cheaply built and cheaply engineered. I suppose they
thought RFI and EMI would be insignificant due to the control being
mounted on the motor... but they're noisy as hell.

Suggestions: Replace the power cables with a shielded, VFD rated cable.
Belden makes a wide variety... I think they're called the VFD classic
line. Pay close attention the unit and cable grounding. Check to be
certain your house ground and neutral connections are only tied together
at the service entrance panel of your home.

My 2 cents...

Jake

"Jake" wrote in message
news:xB85h.54$xD.43@trndny08...
Interesting discussion, folks....

As a controls engineer and High-Voltage electrician.... as well as delving
into HVAC control of late... here's my observations...

These manufacturers will always take the cheapest route possible and damn
the consequences. This is particularly true in power and control systems.

A whole lot of manufacturers are moving toward PWM drives on their blowers
in particular. Many solutions are an 'on-board' frequency chopper that is
integral with the blower's motor.

These choppers are cheaply built and cheaply engineered. I suppose they
thought RFI and EMI would be insignificant due to the control being
mounted on the motor... but they're noisy as hell.

Suggestions: Replace the power cables with a shielded, VFD rated cable.
Belden makes a wide variety... I think they're called the VFD classic
line. Pay close attention the unit and cable grounding. Check to be
certain your house ground and neutral connections are only tied together
at the service entrance panel of your home.

My 2 cents...

Jake

As Jake said.... with the addition of....
Make sure that you have proper earth grounds for your power, and the HAM
rigs/shack. That will go a long way towards eliminating RFI. Make sure that
all the bonding screws in the furnace are clean and tight, make sure that
the furnace has a proper ground also.
When I put the shack together, I drove a seperate 8ft copper ground rod, and
silver brazed #6 solid copper to it, then silver brazed the wire to the
copper ground buss on the back of the bench. All equipment grounded.....no
problem.

de n6ojn

Noon-Air wrote:

SNIPPED

As Jake said.... with the addition of....
Make sure that you have proper earth grounds for your power, and the HAM
rigs/shack. That will go a long way towards eliminating RFI. Make sure that
all the bonding screws in the furnace are clean and tight, make sure that
the furnace has a proper ground also.
When I put the shack together, I drove a seperate 8ft copper ground rod, and
silver brazed #6 solid copper to it, then silver brazed the wire to the
copper ground buss on the back of the bench. All equipment grounded.....no
problem.

de n6ojn



As you describe your setup it does meet USA National Electrical Code. Your home
should have ONLY one earth connection, not two!

As you describe it, your house presumably has the electrical service panel
grounded to an 8 feet long ground rod where the service enters the house. You
seem to have added a second 8 feet ground rod to your home specifically for the
Ham station.

Check with a local electrician for specific compliance issues.

/s/ DD

"Dave" wrote in message
. ..
Noon-Air wrote:

SNIPPED

As Jake said.... with the addition of....
Make sure that you have proper earth grounds for your power, and the HAM
rigs/shack. That will go a long way towards eliminating RFI. Make sure
that all the bonding screws in the furnace are clean and tight, make sure
that the furnace has a proper ground also.
When I put the shack together, I drove a seperate 8ft copper ground rod,
and silver brazed #6 solid copper to it, then silver brazed the wire to
the copper ground buss on the back of the bench. All equipment
grounded.....no problem.

de n6ojn



As you describe your setup it does meet USA National Electrical Code. Your
home should have ONLY one earth connection, not two!

Actually as I live in a lightening prone area, my home has several earth
grounds as do most of the other buildings in the area.

As you describe it, your house presumably has the electrical service panel
grounded to an 8 feet long ground rod where the service enters the house.

The main service panel has 2 ground rods tied to the same buss, The TV cable
entrance has a seperate earth ground, as does the telephone entrance, and
the sub panel in the garage.

You seem to have added a second 8 feet ground rod to your home specifically
for the Ham station.

Yes and that one too.

Check with a local electrician for specific compliance issues.

done did... the sparky is the one that put the extra rods in for the service
entrance and the garage sub panel, and the city inspector signed off on it.

/s/ DD

"Noon-Air" wrote in message
. ..

"Dave" wrote in message
. ..
Noon-Air wrote:

SNIPPED

As Jake said.... with the addition of....
Make sure that you have proper earth grounds for your power, and the HAM
rigs/shack. That will go a long way towards eliminating RFI. Make sure
that all the bonding screws in the furnace are clean and tight, make
sure that the furnace has a proper ground also.
When I put the shack together, I drove a seperate 8ft copper ground rod,
and silver brazed #6 solid copper to it, then silver brazed the wire to
the copper ground buss on the back of the bench. All equipment
grounded.....no problem.

de n6ojn



As you describe your setup it does meet USA National Electrical Code.
Your home should have ONLY one earth connection, not two!

Actually as I live in a lightening prone area, my home has several earth
grounds as do most of the other buildings in the area.

As you describe it, your house presumably has the electrical service
panel grounded to an 8 feet long ground rod where the service enters the
house.

The main service panel has 2 ground rods tied to the same buss, The TV
cable entrance has a seperate earth ground, as does the telephone
entrance, and the sub panel in the garage.

You seem to have added a second 8 feet ground rod to your home
specifically for the Ham station.

Yes and that one too.

Check with a local electrician for specific compliance issues.

done did... the sparky is the one that put the extra rods in for the
service entrance and the garage sub panel, and the city inspector signed
off on it.

Good. Enjoy your ground loops, and have fun replacing appliances the next
time lightning hits close. Don't even think of surviving a direct strike.

"Noon-Air" wrote in message
. ..

"Dave" wrote in message
. ..
Noon-Air wrote:

SNIPPED

As Jake said.... with the addition of....
Make sure that you have proper earth grounds for your power, and the HAM
rigs/shack. That will go a long way towards eliminating RFI. Make sure
that all the bonding screws in the furnace are clean and tight, make
sure that the furnace has a proper ground also.
When I put the shack together, I drove a seperate 8ft copper ground rod,
and silver brazed #6 solid copper to it, then silver brazed the wire to
the copper ground buss on the back of the bench. All equipment
grounded.....no problem.

de n6ojn



As you describe your setup it does meet USA National Electrical Code.
Your home should have ONLY one earth connection, not two!

Actually as I live in a lightening prone area, my home has several earth
grounds as do most of the other buildings in the area.

As you describe it, your house presumably has the electrical service
panel grounded to an 8 feet long ground rod where the service enters the
house.

The main service panel has 2 ground rods tied to the same buss, The TV
cable entrance has a seperate earth ground, as does the telephone
entrance, and the sub panel in the garage.

You seem to have added a second 8 feet ground rod to your home
specifically for the Ham station.

Yes and that one too.

Check with a local electrician for specific compliance issues.

done did... the sparky is the one that put the extra rods in for the
service entrance and the garage sub panel, and the city inspector signed
off on it.

/s/ DD



You bonded all the grounds, eh?

"Oscar_Lives" wrote in message
news:UKS5h.278091$1i1.256793@attbi_s72...

"Noon-Air" wrote in message
. ..

"Dave" wrote in message
. ..
Noon-Air wrote:

SNIPPED

As Jake said.... with the addition of....
Make sure that you have proper earth grounds for your power, and the
HAM rigs/shack. That will go a long way towards eliminating RFI. Make
sure that all the bonding screws in the furnace are clean and tight,
make sure that the furnace has a proper ground also.
When I put the shack together, I drove a seperate 8ft copper ground
rod, and silver brazed #6 solid copper to it, then silver brazed the
wire to the copper ground buss on the back of the bench. All equipment
grounded.....no problem.

de n6ojn



As you describe your setup it does meet USA National Electrical Code.
Your home should have ONLY one earth connection, not two!

Actually as I live in a lightening prone area, my home has several earth
grounds as do most of the other buildings in the area.

As you describe it, your house presumably has the electrical service
panel grounded to an 8 feet long ground rod where the service enters the
house.

The main service panel has 2 ground rods tied to the same buss, The TV
cable entrance has a seperate earth ground, as does the telephone
entrance, and the sub panel in the garage.

You seem to have added a second 8 feet ground rod to your home
specifically for the Ham station.

Yes and that one too.

Check with a local electrician for specific compliance issues.

done did... the sparky is the one that put the extra rods in for the
service entrance and the garage sub panel, and the city inspector signed
off on it.

/s/ DD



You bonded all the grounds, eh?

no, the RF grounds are not bonded to the power grounds.

"Dave" wrote in message
. ..


snip

As you describe your setup it does meet USA National Electrical Code. Your
home
should have ONLY one earth connection, not two!
/s/ DD


I don't know about that! I had some work done which involved an upgraded
service entrance and new breaker panel. The electrician added a second
ground via a ground stake beneath the panel, despite the original (1967)
ground via the cold water inlet pipe being intact and sound.

(I will concede that he didn't quote chapter and verse in the NEC; he may
have been following a local code requirement. I know he wasn't padding the
bill, as he was doing the job at the behest of my son, from whose business
he was buying his supplies. (Still does.)

"Sal"

Motors with brushes are "incidental radiators" according to the FCC. I
believe PWM or variable frequency drive motors would be considered
"unintentional radiators" in that they intentionally generate a radio
frequency (9 kHz to 3,000,000MHz) but do not intend to radiate it. (see
definitions at http://www.hallikainen.com/FccRules/2007/15/3/).

Incidental radiators must use good engineering practice to minimize
interference (see http://www.hallikainen.com/FccRules/2007/15/13/).

Digital devices (I think motor control systems qualify as digital
devices) in appliances are exempt from the emission limits for
unintentional radiators (see
http://www.hallikainen.com/FccRules/2007/15/103/), though the user must
cease operation if the FCC finds it is causing interference.