My heating system uses a constant ignition wiring configuration at the oil burner. This is causing an annoying high level noise in a HF receiver.
I would like to kill the source by improving shielding if that is required. The electrodes are within a metallic housing (e.i., within the burner assembly).
How can the spark gap EMI be suppressed? Would a connection from the burner housing to earth ground be helpful?
Thanks.
The oil burner should already be grounded via the mains connection to it. But a ground if there isn't one should help.
A differential and/or common mode filter will do wonders for noise. My Electric stove was triggering the "lightening detector" and causing my modem to drop out. I got a cheesy filter from some surplus company and ditched the toroid they had and rewound a pair of large ferrite cores with heavy wire to carry the 30 amps the stove can suck. No problems.
I found my communications receiver worked much better with a dedicated ground (10' of 1/2" copper pipe) and not the building ground.. I was getting all kinds of switching transients in the building ground. Receiver ground is at the antenna and less than 5 feet from the receiver with nothing else on it. Building ground was a serpentine path through the attic to the outside service and over 60' of wire.
Direct RFI radiation is seldom the problem - the oil burner ignition is not designed to be an efficient radiator - most of the problem is likely to be via the power lines. For that the source needs a filter and that filter has to be grounded.
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Make sure the spark transformer case is bonded to the firebox to provide an HF path for capacitive spark current back to the grounded center tap of the HV winding.
Add an X rated (across the line AC rated) capacitor across the transformer primary and a ferrite bead over both primary leads, or add a line filter package to the transformer primary, if space permits.
When I disconnect the antenna lead from my transceiver, the interference is gone. Thus, I believe that the problem involves "radiation" across the RF spectrum and does not involve the AC mains.
There is no center tap at this transformer that I know of. The secondary winding terminals in this application are actually spring terminals, that touch the electrodes used for the spark gap only when the (hinged) transformer housing is closed and resting upon the burner chassis (held down by two pressure screws).
I w>V>> My heating system uses a constant ignition wiring configuration at the
What if the mains are not conducting the noise to the transciever, but radiating it to the antenna?
I have the same thing. You can check the center tap grounding with an ohm meter from each spring to case. Make sure you unplug the burner power before risking this. Mine is center grounded, to balance the high voltage between the two electrodes, to discourage an arc from either electrode to the surrounding burner housing.
Mine has some screws on the sides. For this type, I would adsd a jumper wire from one of these to some bolt on the burner box, to guarantee a high frequency path around the painted hinges. There is also a slotted tab that gets clamped down, and a star washer might cut the paint and do the same job.
On Mon, 09 Oct 2006 10:35:22 -0400, John Popelish Gave us:
The spark itself emits. Radiates like a little antenna.
On 9 Oct 2006 19:05:17 -0700, snipped-for-privacy@rica.net Gave us:
More likely that the spark itself is doing that. The radiation it produces is far more broad banded. For the mains to do that, high currents at those frequencies would need to be on them.
On Mon, 09 Oct 2006 22:34:57 -0400, John Popelish Gave us:
With gaps big enough to let out a LOT of HF noise. Certainly not a faraday cage. These sparks are pretty big spikes amplitude wise.
But that spark is inside a metal fire box.
I can really be sure because I can't see what he up against.
Can you get a coffle can to go around it, to shield it for test?
You can also use copper tape or any source of tin.
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If it's radiating through space, then I would think you need a "Faraday cage". This doesn't necessarily have to be made out of solid metal. It can be made out of some sort of conductive mesh screening.
A rule of thumb that I used to use is that the holes in the Faraday cage can be no larger than 1/8 wavelength. So, assuming a maximum frequency of 300 Mhz, for example, you can have holes as large as 4.68".
On 10 Oct 2006 22:36:56 -0700, snipped-for-privacy@yahoo.com Gave us:
Ok fine. Now think about how utterly stupid it would look to walk up to someone with a mesh box made from nearly 5 inch mesh, and say, look at my RF shielded cage!
In fact, I cannot think of a single time I have ever seen such big gaps in a device, and have it still be called or considered to be "shielded".
Science and engineering are not always intuitive. Some people use 1/8 wavelength and some use 1/10 wavelength as a rule of thumb. The theory is that it requires 1/4 wavelength to make an antenna and 1/8 and 1/10 are significantly below that. Do you work as a compliance engineer? What sort of rule do you use?
What aperture size would you allow for a microwave oven at 2450 Mhz? What aperture size would you allow for submarine ELV signals at 76 Hz?
One reason electronic devices have smaller holes is that they are concerned with much higher frequencies.
At 2.4 GHz I would prefer solid aluminum walls with the seams bonded, like an old portable shielded computer room. At the least, I would want a double shielded room made of fine woven bronze screening, and a double layer copper clad door with finger stock all around the seams and the two shields bonded only where the power comes in. I've worked in both types of shielded rooms. I designed a foil shielded room built on 2" foam panels and covered with wood paneling, but I haven't built it yet. I have to put a new roof on my shop, first.
Do you know the wavelength of 76 Hz?
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
If you were building a microwave oven, though, what is the largest aperture you would allow to seal the door or the window, for instance?
If you think you might ever run a generator in your shop, by the way, I would put sheet rock on the ceiling (walls also) and fiberglass insulation.
According to an online calculator the wavelength for 76 Hz is
12,947,368.421 feet (2452 miles). The wavelength for 2450 Mhz, incidentally, is 4.82 inches. I've always wondered, incidentally, if my subwoofer would sound better if I built a room 1/4 wavelength long at it's lowest frequency. I haven't done it yet, though :>Me too--3 years--U.S. Army. I've lost everything else over the years, including all my year books, but I still have my DD214. I'm not sure why. Maybe subconciously I wanted to make sure they didn't call me up accidently :>
No, the foam panels are quite rigid, and they carry the weight of each panel. Heavy aluminum foil is glued on each side, and over the edge where the panels join. You leave at least a half inch gap all the way around the edge to be sure they don't touch. Then you glue thin paneling or hardboard to each side to protect the foam and foil. The corners and edge joints are the secret, they hold everything together and connect the inside and outside foils into a pair of separate but continuous shields. Finally, you bring power in somewhere and bond the two shields. You can make a pair of holes for air conditioning, as long as you are careful to maintain the shielding with bronze screening. I'll put plenty of pictures on my website as I build it. You can build a 12'
Sheet rock if fairly heavy, so you paint the ceiling panels white, or another light color.
A generator, as in Gasoline powered? It would be in a separate building, by the automatic transfer switch.
A simple steel box will stop 76 Hz.
It would cause a resonance over a narrow range of frequencies and sound like crap, unless all you want is a vibration that will shake the walls apart.
You can get full copies of your military records by applying to the VA directly, or through your local Veterans Service Officer. A local DAV post should have at least one, and sometimes the county government has one, too. I have both, locally, and have had help from both at different times.
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
A scrap shipping container (welded steel) makes a good start for a shielded room, if you've got the real estate.
My rule of thumb is: if the wavelength is farther than you'd want to walk, it's VLF :-)
--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
(Stephen Leacock)
I'm not zoned for it, or I would already have a couple of them. I would have to put them in my driveway and my neighbors would complain, loudly. :(
Some days that would be up around 100 MHz.
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
how do you intend to bond the edges of the aluminium sheets ?
do you have some sort of spot-welder?
Bye. Jasen
Aluminum tape with conductive glue.
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
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