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1-5 of 5 messages
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Page 1 of 1
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RHEEM HVAC WITH AUXILLARY HEAT
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by KB5WHX on October 4, 2009
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Hello,
I have a Yaesu FT-840 running into a MFJ-989C tuner. The coax from the tuner goes into the wall of my radio room and into the attic via pvc pipe then out the eaves to a common point ground. My antenna is a G5RV and is a reasonable distance away from my house (hieght is 40').
When my AC system kicks on I get RFI accross the bands.
If I turn the AC system off but turn the fan on I still get the RFI. I can actually hear the RFI slowly increase as the fan reaches maximum speed. I disconnected the antenna from the common point ground and then disconnected the coax that comes from the tuner at the ground point and noise got worse. The coax in the attic my be about 10'-12' from the HVAC fan assembly, but I cannot move it any further away. Another test I performed was to leave the coax connected at the common point ground however I disconnected the coax at the tuner. The noise (RFI) dropped out completely. I am far from an expert on this but I beleive the stub of coax (50') from the tuner through the attic and to the common point ground is picking up the RFI from the HVAC fan motor. My equipment in my shack is not grounded for RFI. The common point ground I speak of is simply a 5/8"x8' ground rod with a piece of aluminum plate attached to it via ground rod clamps (Ox-Gaurd was used due to disimilar metals) the aluminum plate has a Pl-259 Bulkhead connector attached to it. In the event of thunderstorms I leave the antenna grounded to the rod but I disconnect the coax which feeds my equipment and move it up and way from the ground rod. All of my radio gear is unplugged from line during storms. Should I ground my equipment to stop the Fan produced RFI and is the existing ground rod to far away (50'). Would a higher quality coax (Foil wrapped Shield) help in keeping the RFI out of the coax. One thing I have never seen addressed is can and how could coax be shielded from RFI. Would metal, plastic or copper pipe help reduce RFI. Any assistance, recommendations on how to solve this RFI issue would be appreciated.
Thank you
Steve
valleys@bellsouth.net
KB5WHX
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RE: RHEEM HVAC WITH AUXILLARY HEAT
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by W6OP on October 4, 2009
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If this is a new unit have the dealer that installed it contact the manufacturer for an RFI kit. They should do it for free. I have an American Standard which I think is the same manufacturer and they put it in and reduced the interference substantially.
Pete W6OP
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RE: RHEEM HVAC WITH AUXILLARY HEAT
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by KB5WHX on October 12, 2009
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The unit was installed in 2004 and the dealer has since went out of business.
The blower motor is a GE ECM 2.3 Motor. I have read their literature regarding grounding the blower housing to the ground on the input voltage line. This appears to have been done.
I used an AM radio and found that the noise was strongest near the thermostat and return air area. I accessed the attic and placed the radio near the thermostat wires and the noise was much stronger at that point than the cabinet that houses the blower motor. Apparently, the thermostat wires are picking up the RFI or EMI and carrying the noise down to the thermostat which is just outside my radio room.
Short of running shielded thermostat wire is their a choke or filter that I can install on the thermostat wire?
Just a footnote. Even though I hear the noise through the receiver and the volume is reasonably loud it does not move my S-Meter.
Thanking everyone in advance for their comments and assistance.
Sincerely Yours,
Steve
KB5WHX
valleys@bellsouth.net
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RE: RHEEM HVAC WITH AUXILLARY HEAT
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by WB4BYQ on October 13, 2009
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please check the following information that i have, there much information on this forum on how to help with this problem.
http://olympixcorp.com/rfchoke/ferrite.htm
http://www.dxengineering.com/Parts.asp?ID=1128&PLID=182&SecID=152&DeptID=42&PartNo=DXE-CSB-COMBO
http://atnm.mcars.us/HomeBrew/WB4BYQ/CommonModeChokes/
there is a very good engineering document that i cannot remember its location. it is posted in the rfi section, i hope the amateur that knows will post it.
wb4byq
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RE: RHEEM HVAC WITH AUXILLARY HEAT
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by WB4BYQ on October 13, 2009
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here is the location of the rfi, choke, etc. technical
posting.
http://www.audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf
wb4byq
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