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HF Transmitting Causing Lights to Flicker



I live in a HOA neighborhood. As a result, the can be no exterior antenna. The solution was an OCF Dipole in the attic. 

When transmitting on the HF bands the lights that are connected to electronic dimmers will flash on and off, and the electronic thermostat to change program and settings.

I have tried using a clamshell choke on the thermostat wires to no effect.

I have not tied that on the dimmer wiring.

Is this the best way to go, or should I be looking at putting a choke at the feed point of the antenna?


Any help would be appreciated.


73 Bob KD9TGU

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The common mode choke on the antenna feedline will help the radio, not the LED. To be effective, you have to put chokes on the LED side, which you can't because it's all hidden wiring.

Just to do a final debug, do the LED bulbs go off if they are installed in a socket that is not controlled by a dimmer? Let's just make sure it is not the bulbs (90% sure it's not). As for a really good explanation of chokes on the 'appliance' side, vs. the radio side, https://www.coilcraft.com/en-us/edu/series/a-guide-to-understanding-common-mode-chokes/ - They actually make the chokes that are installed in appliances, hifi, TVs, etc. Of course they are more focussed on high frequencies, which is not your issue. But the explanation is one of the better ones.

My instinct tells me that if you want to keep your antenna where it is, if you want to continue feeding it the current power level (and maybe some day more), you are indeed better off going the on/off route (not as pretty, I know).

Last note... In re-reading your original post, I would try one more thing. I would look for any electrical wires near the antenna in the attic. Those are the ones most likely to be feeding the hf into your house power lines. If you do find some that are there, as a test, kill the breaker on those lines and see if the interference stops. If it does, then you might want to put chokes on those lines only, thus preventing the signal from propagating throughout the house. Just a thought.

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Hi Bob.

Welcome to one of the hardest simple problems to fix! The dimmer is picking up the signal, period. Some will tell you it's because the dimmer is actually a PWM and that you're changing the duty cycle of the AC waveform. Others will tell you that the dimmer is simply acting as an antenna. Regardless, the problem is fixing the flicker and that's difficult to do. Many have tried toroids near the dimmer but that means, if it's a wall dimmer, digging into the wall! Not ideal, right? If the dimmers are external, then you might have a chance with, as you suggest, some good ferrites. Another solution is to use a smart bulb with dimmers built in. They are usually immune but I don't know how many bulbs we're talking about. If you're dealing with 25 bulbs, that's going to cost you; if it's three bulbs in the living room it's a worthwhile option.

Quick questions:

  1. Problem on all HF bands?
  2. Same (or similar) flicker frequency on all bands?
  3. To fully debug, and to confirm or rebuke my assertive "it's the dimmer" statement, do you have any tungsten filament bulbs lying around (obviously with the same size socket). Try those just to put your mind to rest that it is indeed the dimmer.

Add anything else you may not have thought of.


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I happens on the HF bands only. VHF and UHF are no problem.

They are wall mounted dimmers. They are 3 way devices controlling LED fixtures.

The total number of bulbs is 12, so it could be expensive.

Is a common mode choke going to help any?

There is no room in the box to put a ferrite on the wiring.

When I said flicker, it means that the lights go off completely when transmitting, and then come back on when I un-key.

I may try changing the dimmers with something that is more mechanical than electronic.


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