Electrical interference from bathroom below rooftop antenna

A2J33P · 31-Jul-2017, 10:30 PM

Our rooftop antenna is mounted on a tripod directly above our master bathroom. There is about 2' of attic space between the shingles and the bathroom ceiling.

Whenever my wife is using her hairdryer, Digital channel 39 pixilates to the point of being unwatchable, so my question is...

Is there some sort of shielding that I could put in the attic between the bathroom and the antenna to prevent the interference? Chicken wire? Aluminum foil?

Although the problem is reproducible 100% of the time that the hairdryer is on, realistically, it's actually infrequent that I am watching or recording something on that channel at that precise time. Therefore, my question is more academic than anything else. I'm just curious at to this group's thoughts, and I'm willing to try out any reasonable suggestions.

rabbit73 · 1-Aug-2017, 12:39 AM

Interference can be radiated or conducted by the power line or both. The shielding in the attic would help to reduce the radiated interference, but it might be coming in to the TV over the power line.

Is the coax grounded with a grounding block that is connected to the house electrical system ground?

It is often necessary to block the interference at the device causing the interference with an AC line filter if it is being conducted over the power line.

Interference problems can be difficult to solve, especially if channel 39 is weak.

A2J33P · 1-Aug-2017, 2:35 AM

Quote:

Originally Posted by rabbit73

Interference can be radiated or conducted by the power line or both. The shielding in the attic would help to reduce the radiated interference, but it might be coming in to the TV over the power line.

Is the coax grounded with a grounding block that is connected to the house electrical system ground?

It is often necessary to block the interference at the device causing the interference with an AC line filter if it is being conducted over the power line.

Interference problems can be difficult to solve, especially if channel 39 is weak.

Thanks Rabbit...

All grounding is proper. Mast (via its own copper line) and coax (via grounding block) are grounded to a 6' grounding rod. That grounding rod is bonded to the house electrical system ground.

It is always possible that the interference is conducted via the power line, however, a few years ago I installed LED lights in that bathroom's ceiling cans (directly below the antenna), and suddenly I would lose a couple of channels (39 included) whenever those lights were on. I moved those LED lights from that location to another place in the house, and problem solved. Because of this, I suspect the LED bulbs and the hairdryer cause radiated interference, being so physically close to the antenna.

Channel 39 is in fact my weakest channel, so it doesn't take much to lose a tunable signal. If I have this correct, Channel 39 is 623 Hz which has a 480 km wavelength, meaning chicken wire should be able to block that frequency. However, I'm trying to block whatever frequency the hairdryer is transmitting.

Again, this whole exercise is completely academic as I am primarily interested in understanding the mechanics of the problem. If we can solve it in the process, that would be a bonus!

JoeAZ · 1-Aug-2017, 3:21 AM

Your issue would be much easier to understand if the interference
occurred on low band VHF. It would be interesting to plug the hair
dryer into a heavy duty extension cord which was plugged into a
distant wiring circuit. If the problem disappears, the issue is probably
with the circuit. If the issue remains, it is more likely interference.

Tower Guy · 1-Aug-2017, 12:49 PM

The interference from the hair dryer to the antenna can be direct, as you suppose, and could be reduced by chicken wire. The other method of transmission is down the power cord and through the house wireing and perhaps into the attic light and then the antenna.

If it's carried down the power cord, a ferrite bead, such as those bulges at the end of a VGA cable, clamped over the hair dryer cord, can minimize the problem. A more surefire solution is to get the antenna on the roof.

rickbb · 1-Aug-2017, 2:27 PM

Could be as simple as the hair dryer and the TV are plugged into the same circuit. Although code nowadays requires bathroom outlets to be separate ground fault interrupt circuits.

Try moving the hair dryer around the house to see if you isolate it down to a power line issue. If you can then a power line stabilizer/filter on your TV might solve the problem. Ferrite beads on the cords could also help too.

You might have to do both the line filtering and the chicken wire if you really want to solve it.

A2J33P · 1-Aug-2017, 2:29 PM

JoeAZ ... I followed your suggestion and tried the Hairdryer on a separate circuit via an extension cord. The interference existed when the hairdryer was "on" in the bathroom under the antenna, but the interference stopped as I walked with the hairdryer into a different room that is not under the antenna.

Tower Guy... The antenna is on a tripod and mast on the roof (drawing attached). As you suggested, I put a ferrite core on the hairdryer power cord and the interference still exists when the hairdryer is on.

These are great questions and suggestions! This additional information still leads me to believe that the interference is directly transmitted from hairdryer to antenna.

A2J33P · 1-Aug-2017, 2:43 PM

rickbb... great points! The house is three stories and we have four TVs. Each TV is in its own room, and I have verified that each is on its own separate circuit. All TVs experience the interference when the hairdryer is on and in the area directly below the antenna, leading me to believe that the antenna is the common entry point of the interference.

That bathroom is about to undergo a major remodel starting next month, during which, wiring and insulation changes will be made in that attic space. During that time, I will staple up a few rows of chicken wire on the rafters below the antenna, and the experiment will continue!

rabbit73 · 1-Aug-2017, 3:07 PM

Chicken wire has large spaces. Don't staple it down until you make a test by laying it down first. You might have to use a finer mesh like hardware cloth with 1/4" squares. It might also need to be grounded; try it with and without.

A2J33P · 1-Aug-2017, 3:51 PM

Hardware cloth would be perfect! $33 for 24" x 50'. That would cover an 8' x 12'

I never considered grounding it since it would be in the attic, but it would be worth a try since I'm gong this far with the project.

Tower Guy · 1-Aug-2017, 6:23 PM

1" chicken wire would be more than adequate.

Another approach would be to move the antenna to the other end of the house

ADTech · 1-Aug-2017, 6:42 PM

... or move the hair dryer to the other end of the house...

A2J33P · 1-Aug-2017, 7:35 PM

There was some serious trial and error in choosing that spot on the roof. We are surrounded by very tall trees, and that spot shoots right through the one strategic spot. So, whereas the hairdryer is an occasional source of interference, the trees would be a continuous source.

As far as moving the hairdryer... it'd be easier to move the trees.

ADTech · 2-Aug-2017, 12:32 PM

I'd try a new hair dryer first. You might find one with an electric motor that doesn't spew RFI during operation.

A2J33P · 2-Aug-2017, 4:07 PM

Quote:

Originally Posted by ADTech

I'd try a new hair dryer first. You might find one with an electric motor that doesn't spew RFI during operation.

Great suggestion... We just happen to have three hairdryers in the house, which I tried as you suggested... All three yield the same interference when operated in that general area.

Thank you to everyone for sharing your new and different perspectives on this topic. Again, the situation itself is so rarely a problem that it I find it more interesting than irritating.

My plan is (in the interest of science) to staple some shielding (probably Hardware Cloth) to the rafters in the attic, directly below the antenna. I'll do this during the bathroom remodel project which should start soon and be finished by October. I'll report back when the results are in!

Tower Guy · 2-Aug-2017, 9:09 PM

Potential solution # 3, a brushless hair dryer;

https://www.amazon.com/Infiniti-Cona.../dp/B00MO78Z86

A2J33P · 2-Aug-2017, 9:43 PM

Quote:

Originally Posted by Tower Guy

Potential solution # 3, a brushless hair dryer;

https://www.amazon.com/Infiniti-Cona.../dp/B00MO78Z86

Tower Guy... that... is... BRILLIANT!

That is some serious thinking outside of the box!

I just ordered it... My wife is going to be so confused. Fortunately for me, she's a great sport!

Tower Guy · 2-Aug-2017, 10:51 PM

My wife has one of those hair dryers. She loves it. So does our daughter. They work extremely well.

But to be fair to ADtech, he suggested a different hair dryer first.

A2J33P · 2-Aug-2017, 11:03 PM

Quote:

Originally Posted by Tower Guy

My wife has one of those hair dryers. She loves it. So does our daughter. They work extremely well.

But to be fair to ADtech, he suggested a different hair dryer first.

That's right, he did!

Sorry if I missed that, ADtech... I took your post to mean that maybe we just had a bad/old/tired hairdryer, and maybe a different/newer one might make a difference. I had no idea that there were brushless hairdryers out there!

Group effort!

ADTech · 2-Aug-2017, 11:07 PM

Quote:

Originally Posted by A2J33P

That's right, he did!

Sorry if I missed that, ADtech... I took your post to mean that maybe we just had a bad/old/tired hairdryer, and maybe a different/newer one might make a difference. I had no idea that there were brushless hairdryers out there!

Group effort!

Nope, you understood what I meant.

Heck, I didn't even know here were breathless hair dryers (since I don't have much of a need for one anymore) either.