Also, my current probe sensitivity is 30 dB less that the actual power.
That is to say if I put 0dBm into a 50 ohm resistor and sample one lead
of the circuit, my current probe will show - 30 dBm. So the spectral
components reported at the -90 dBm level would actually represent -60
dBm components due to the current probe.
Tom W0IVJ
On 1/10/2015 2:24 PM, Tom Thompson wrote:
I forgot to add that the measurements that I made where I saw energy
were differential.
Tom W0IVJ
On 1/10/2015 10:43 AM, Tom Thompson wrote:
I just made some light bulb measurements using an RF current probe,
an oscilloscope, and a spectrum analyzer. My current probe is flat
within 3 dB from 500 kHz to over 50 MHz. The common mode current on
all bulbs was negligible through the entire HF band. The compact
fluorescent and LED lamps had energy below 1 MHz but above 1 MHz the
energy was down 70 dB. The LED lamp had a switching speed of about
25 kHz. There appeared to be no spectral components at the -90 dBm
level between 1.8 and 30 MHz. The bulbs used were a 200 watt
incandescent, a GE 26 watt helical compact fluorescent made in China,
and a FEIT 60 watt replacement LED that uses 9.5 watts made in Taiwan
and available at COSTCO. I can email the spectral plots to anyone
interested.
73, Tom W0IVJ
On 1/10/2015 5:52 AM, Greg Troxel wrote:
wa4tuk <wa4tuk-rf@comcast.net> writes:
Thank you for posting your results. Information about what makes noise
and what is (relatively) quiet is hard to find. I will say I am
surprised. So far I have avoided LED lamps (A19 style) and use a mix
of incandescent and CFL where appropriate.
I was surprised when I got the first one.
I would have thought the switching rate would have been in the 100kHz
range with harmonics radiating.
Please note that I said I have other RFI sources; an attic antenna is
not a good situation to start with. I had dealt with a number of them,
but the base level was higher than I expected yesterday. So it's
possible that these are problematic in quieter situations. Also, I
didn't sweep everywhere, so if there is a square wave spectrum that's
pretty limited to harmonics, I could well have missed it.
Given that these cost only $5ish these days (and that you may want to
preserve your stockpile of pre-ban bulbs :-) it seems worth buying one
or two to try out to see if you can hear them.
(Power supplies for LED strip lighting seem to be an entirely different
situation.)
73 de n1dam
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