consumer product RFI Sheilding - required?
Hon1nbo, Mon Oct 06 2008, 01:59AMOk, today I just got my first oscilloscope off of craigslist (it was free, so I figured it would get me started: it is dual trace at 10MHz, good enough for most of my stuff... and only cost was the gas to pick it up)
anyways, I decided to use a dedicated, hot shoe camera flash to test things out. So I hook the probe to the hot portion of the show, and the ground to ground. At this point i did not know how to turn off the second trace (never liked manuals lol) and I decided to plug it in to something, but since I didn't have a probe, I plugged in a BNC rubber duck antenna.
The second trace with the antenna was nearly identical to the camera charging circuit trace...
to test if it was the scope doing this, I detached the probe and ground from the flash and the scope, and the trace still showed the charging circuit's trace.
I turned off the flash and the trace was gone, after turning it back on, I fired the flash and watched the trace do the same thing as when the flash was connected...
Then, while the flash was on I moved it around in 3D space and the trace adjusted itself, even when my hand was brought in proximity of the flash rather that the antenna..
So here is my question: Doesn't the FCC or someone have rules about spurious RF emissions from consumer hardware?
Should the flash put out this much? (it is a strong signal from a few feet...)
Re: consumer product RFI Sheilding - required?
Proud Mary, Mon Oct 06 2008, 10:11AM
This sounds like a hand capacitance effect which you will always get around high impedance inputs.
Proud Mary, Mon Oct 06 2008, 10:11AM
This sounds like a hand capacitance effect which you will always get around high impedance inputs.
Re: consumer product RFI Sheilding - required?
Dave Marshall, Tue Oct 07 2008, 12:14PM
The FCC has strict regulations regarding the level of unintentional radiation permitted. Most appliances have a statement somewhere on them regarding compliance with FCC Part 15 regulation.
The flash uses an inverter to get the ~330v it requires to charge the capacitor. As most hams have found out, cheap inverters and SMPSes are amazingly good at fouling up the RF spectrum. The waveform they use to drive the transformer is rich in harmonics, and there is zero filtering.
Any electrical appliance can become a radiator when old or damaged. Some appliances have a certain degree of inherent RF emission just due to their nature. Generally the FCC doesn't care about these incidental radiators until a part 15 complaint (interference with licensed users of the RF spectrum) is filed.
Dave
Dave Marshall, Tue Oct 07 2008, 12:14PM
The FCC has strict regulations regarding the level of unintentional radiation permitted. Most appliances have a statement somewhere on them regarding compliance with FCC Part 15 regulation.
The flash uses an inverter to get the ~330v it requires to charge the capacitor. As most hams have found out, cheap inverters and SMPSes are amazingly good at fouling up the RF spectrum. The waveform they use to drive the transformer is rich in harmonics, and there is zero filtering.
Any electrical appliance can become a radiator when old or damaged. Some appliances have a certain degree of inherent RF emission just due to their nature. Generally the FCC doesn't care about these incidental radiators until a part 15 complaint (interference with licensed users of the RF spectrum) is filed.
Dave
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