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Author Topic: CW - Porch light brightens on key down  (Read 8642 times)
KE6TDT
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Posts: 73




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« on: September 22, 2011, 11:33:44 PM »

Equipment, ICOM 746 using MJF 949D AT, while keying on 75 meters at 100 watts, with a homemade inverted V,fed with 300 ohm twin lead, no amp, only 100 watts. The V and turner works well, getting everything down very close to 1/1.

Tonight  I just happened to notice a reflection at my station. I looked behind me through the window, and saw my porch light brighten every time I keyed.   I mean it was doubling in brightness and extremely responsive to every key down. 

The light is a regular porch light type fixture, but with the bulb is screwed into a threaded light sensor, which is screwed into to where the bulb would normally screw in. I suspect it caused some previous receive interference based on the fact when I have previously turned the light off, the slight interference went away.

In any event, I put the tuner in dummy load, and it it stopped making the porch light brighten on key down. 

When I switched to the vertical no issues and only does this when using the wire antenna, which the center mast is center on the roof about 26 feet high, above the roof line.   

In addition, when I went to the 40 meter CW band, no issues with the porch light. This seems to be isolated to 75/80 meters with ONLY the wire inverted V. 

My radio is not grounded, as I have no access to ground. 

Any comments, or suggestions?

Dan

 

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STAYVERTICAL
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Posts: 875




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« Reply #1 on: September 23, 2011, 12:18:19 AM »


Hi Dan,

If the light gets brighter it must have more current going through it when you key down.
If you are using an ordinary incandescent lamp then it is unlikely your RF is going to increase the voltage on the line
sufficiently to double its brightness.
But if it is a compact flourescent lamp, the gas inside it can be excited by RF and so be increased in brightness.

Alternatively, the screw-in sensor probably has a solid state switch of some type to turn the light on and off.
The power switching semiconductor may have RF exciting its input, so giving a higher duty cycle and letting
more current flow through the lamp.

If the lamp is a wire filament type, the problem is probably the sensor, which if you can unscrew it easily,
would be a way of determining what the problem may be.

Good luck, and look on the positive side - your neighbours who were in the navy will be able to follow along
with your qso like an aldis lamp (hi).

73s
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W8JI
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Posts: 9296


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« Reply #2 on: September 23, 2011, 01:57:55 AM »

Dan,

When I lived in the city with my antenna over my roof, I used to light my neighbor's porch light with my radio. No diodes, no CFL lights. Just a normal bulb. When the lamp would be on and I transmitted, it would get extremely bright!!! Much brighter than normal.

Unless you have a dimmer on that bulb, you probably have the problem I had. The light wiring below the antenna is acting like an antenna and the RF energy from the wires is energizing the bulb. This adds to the heat from nomal voltage.

This is almost never anything to do with anything but the antenna being close to and parallel with house wires. It takes no diodes or anything else to cause it, although diodes and switches and other things can influence the results.

The solution is generally move the antenna, unscrew the bulb, or add a UL/CSA bypass capacitor across the lamp socket....which is usually not 100% safe. 

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KA4POL
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Posts: 2089




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« Reply #3 on: September 23, 2011, 02:12:35 AM »

Watch for patent infringement  Grin: http://www.witricity.com/pages/technology.html
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N4NYY
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Posts: 4816




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« Reply #4 on: September 23, 2011, 07:24:33 AM »

Quote
When I lived in the city with my antenna over my roof, I used to light my neighbor's porch light with my radio. No diodes, no CFL lights. Just a normal bulb. When the lamp would be on and I transmitted, it would get extremely bright!!! Much brighter than normal.

Damn. You must have had fun with him on Halloween.
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KE6TDT
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Posts: 73




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« Reply #5 on: September 23, 2011, 09:26:04 AM »

I suspected that.

Thanks Tom.

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KE6TDT
Member

Posts: 73




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« Reply #6 on: September 23, 2011, 09:28:24 AM »


STAYVERTICAL,

Thanks for that. I will do some more testing tonight, but I suspect you are correct and or the power line going to the light, is simply acting as an antenna.
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N3OX
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« Reply #7 on: September 23, 2011, 09:47:18 AM »

Watch for patent infringement  Grin: http://www.witricity.com/pages/technology.html

I wouldn't worry about that.  The tenth edition of the ARRL Antenna Book uses very similar resonant inductive coupling to couple power to a rotary beam antenna. Grin  I adapted it for use with ultrasound velocity measurements in my rotating Ph.D. experiment: http://n3ox.net/files/us_ring.jpg 




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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
VE3FMC
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Posts: 1001


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« Reply #8 on: September 23, 2011, 11:04:42 AM »

I used to light up the string of Christmas lights on the house eaves like that.

Oh, wait. That is because I had them fed with the extension cord going to my tuner not the AC outlet  Grin On 40 meters with the amp on they flickered off and on and looked real good!

I wish I could brighten up my neighbor's lights. Or just brighten him up period.  Roll Eyes
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TANAKASAN
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Posts: 933




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« Reply #9 on: September 23, 2011, 11:18:06 AM »

If you're worried about adding a 110v rated capacitor across the porch light power then consider using series inductance instead. A couple of those clip on ferrites which are used on monitor leads should do the business.

Tanakasan
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AA4HA
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Posts: 1583




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« Reply #10 on: September 23, 2011, 01:11:21 PM »

I wish I could brighten up my neighbor's lights. Or just brighten him up period.  Roll Eyes

My neighbors are pretty dim bulbs in general. I think their family tree probably looks more like kudzu.

The same guy who hunts turkeys while sitting in his front yard, in a folding chair set up in the back of his pickup truck. Cooler of beer, shotgun and a box of shells. Doors open on the pickup truck while a tape of turkey calls plays constantly on the cassette player in the truck. If something moves in the bushes (on my property) he shoots at it. All of this out of season for turkey hunting. I did not know that you could be that lazy while hunting.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
W8IXY
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Posts: 9




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« Reply #11 on: September 23, 2011, 02:28:44 PM »

If your RF is being converted to heat/light in a bulb attached to enough wire to act as an antenna, then wouldn't that absorbed power be "burnt up" rather than radiated to the intended recipient?   If you are feeding 100 watts to your antenna, and 15 of those watts are being burnt up by the light, then of the 100 watts you are radiating, only 85 of them are doing you any good.  Plus, if the light bulb and associated wiring is literally part of your antenna system, it can act as an additional "element" in the antenna system and add some directional effects.  Of course, in the real world one or two db rarely will make a difference in most communication paths.

In my novice days over 50 years ago, I had a DX20 that probably put out 40 or so watts on 80 meters.  I had a long wire draped over the house.  I lit up an upstairs light to half brilliance when I keyed the DX20.  And, that wire never sent much RF into the ether.  Hardly ever made a contact on it.

73
Ted  W8IXY
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K8AXW
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Posts: 3958




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« Reply #12 on: September 23, 2011, 11:09:32 PM »

Back in the day.....KW AM, houses jammed together..... guy I knew used to drive his neighbors crazy with their ceiling lights pulsing with RF and 3:00AM! (AC power off)
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N4OZ
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« Reply #13 on: September 27, 2013, 04:25:33 PM »

Am AM broadcast station in my home town in Australia once had a perplexing problem with a marked "hole" in their radiation pattern. Their transmitter tower was mounted at the rear of their lot, which backed onto the soft mud bank of a tidal and therefore salty river. For years this excellent "wet groundplane" had allowed them to have great coverage, but it was clear a problem had developed in their reception area. The poor coverage was approximately along the axis of the road frontage, but in one direction only. I should also tell you that the radio station was set amongst residential housing, which had been there as long as the broadcaster.

As far as the engineer could tell, nothing had changed at his site with the tower, transmitter, transmission line or ground connection. Listener's reports of reduced coverage were indeed verified by his field testing.

It was this same engineer who who noticed a neighboring house that was always well lit, at a time when people would turn their lights off at night, and certainly not leave them on 24/7.

His detective work revealed that his neighbor had constructed a "tank circuit" (as the story was retold to me) and was using the nearby transmitter to power his lights! This was found to be legal at the time because the resident had a valid radio listener's license and no action could be taken. Yes, you used to need a license just to own a radio set - this is an old story.

The ultimate solution was for the broadcaster to pay the clever freeloader to remove his circuitry and therefore restore radiation pattern. This was retold by many of the older guys at my ham club who used to also include the name of the engineer and thus was something of a local legend Smiley

I hadn't thought about this in years until I saw this post.
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AA4PB
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Posts: 12981




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« Reply #14 on: September 27, 2013, 05:10:51 PM »

Is the light sensor one of those that turns on/off gradually to save the bulb? If so, the wiring could be acting as an antenna to pick up the RF and feed it into the sensor. The sensor essentially has a dimming circuit in it that could be applying full power to the bulb in response to the RF.
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