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Author Topic: Central Air Fan turning on when transmitting  (Read 422 times)

WA2CWX

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Central Air Fan turning on when transmitting
« on: December 19, 2020, 07:49:32 PM »

I live in an HOA, unfortunately, and have a dipole in the attic which is where the central air Fan unit is located. The compressor is outside. Whenever I key the transmitter, TS-440S, the fan turns on. When I stop, the fan will turn off in about 3 minutes. Any idea what I might try? Moving the antenna to the outside is an option but I must use lots of STEALTH!! Thanks in advance.

Mike, WA2CWX
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N6BIZ

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Re: Central Air Fan turning on when transmitting
« Reply #1 on: December 19, 2020, 08:39:55 PM »

K9yc
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AB6RF

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Re: Central Air Fan turning on when transmitting
« Reply #2 on: December 19, 2020, 09:17:38 PM »

Does your furnace / thermostat have a fan-only option?  Sounds like yes...

Most likely the RF gets on the thermostat wires, and the rectified RF voltage turns on the fan.
The thermostat wires are totally unshielded, not even real twisted pair, so when those wires only some feet or maybe few tens of feet away from a HF dipole, they pick up a lot of RF energy.

Common-mode choke (the reference to K9YC cookbook) on the dipole feed point might help, but maybe even more likely a 0.01uF capacitor from each thermostat control wire to the common wire  (at the furnace end of the thermostat wires).
If that didn't help, then I'd add the 0.01uF caps also at the thermostat.
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K1KIM

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Re: Central Air Fan turning on when transmitting
« Reply #3 on: December 20, 2020, 05:32:16 AM »

Is your thermostat also controlled via phone/tablet wifi/cell?

I have 3 HTs. Only one will turn my paper shredder on in my office if the shredder is set on auto. This is even on low power 1w.

I'm going to try some ferrite beads on the ac input linr to the shredder or just keep it off until needed. The HVAC issue is a bigger issue.

Keep us posted!
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KA1CUH

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Re: Central Air Fan turning on when transmitting
« Reply #4 on: December 20, 2020, 08:47:13 AM »

When I transmitted on hf my furnace relays would chatter. I have three zones so I put two snap on
ferrite beads on each thermostat wire near the control box that stopped it.
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KF5LJW

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Re: Central Air Fan turning on when transmitting
« Reply #5 on: December 20, 2020, 08:57:46 AM »

Hams sure like shooting themselves in the foot. Gives them something to do the rest of their lives trying to make a compromised system work. You put an antenna in the attic or within two wave lengths of the house, then complain about RFI/EMI. You got exactly what you asked for.
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W7CXC

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Re: Central Air Fan turning on when transmitting
« Reply #6 on: December 20, 2020, 10:07:13 AM »

KF5LJW....Don't think he was complaining , just asking for some help. RELAX!
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K1KIM

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Re: Central Air Fan turning on when transmitting
« Reply #7 on: December 20, 2020, 04:57:29 PM »

Hams sure like shooting themselves in the foot. Gives them something to do the rest of their lives trying to make a compromised system work. You put an antenna in the attic or within two wave lengths of the house, then complain about RFI/EMI. You got exactly what you asked for.

WOW. Sure glad he doesn't have a 80M long wire.  493' from the house is quite a bit!
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G8FXC

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Re: Central Air Fan turning on when transmitting
« Reply #8 on: December 20, 2020, 11:34:20 PM »

Hams sure like shooting themselves in the foot. Gives them something to do the rest of their lives trying to make a compromised system work. You put an antenna in the attic or within two wave lengths of the house, then complain about RFI/EMI. You got exactly what you asked for.

With modern housing, if we followed that principle the bands would be pretty empty now!

Martin (G8FXC)
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N4EF

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Re: Central Air Fan turning on when transmitting
« Reply #9 on: January 06, 2021, 03:30:51 AM »

I also have an attic dipole, live in an HOA, and use a TS440s.

You’re fortunate that it’s only your fan that’s triggered by the transmitter.

My house intrusion alarm would activate anytime I transmitted more than 10 watts.

The problem was solved with snap-on ferrite cores on all of the wires entering the home alarm control box. I now can transmit full barefoot power without triggering the alarm.
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