[Elecraft] OT: LED Light Bulbs

[Jim Brown]

A year or two ago, W3LPL taught us that this is the result of passive 
intermod generated either by the diodes or the SMPS or both. We see this 
in our CW contesting trailer, where CW operating frequencies on 80, 40, 
and 20 are harmonically related. We run K3, P3, KPA500, KAT500 to 
individual single-band dipoles with feedpoints within a few feet of each 
other. The 40 and 80 feedlines both have double stubs, placed along the 
line to maximize their effectiveness per this app note 
http://k9yc.com/LocatingStubs.pdf  and all antennas have common mode 
chokes at the feedpoint.

If we park in the middle of nowhere, the stubs bring the power amp 
second harmonic down to the point that we can operate within 10 kHz or 
so of it. If, however, we set up close to civilization, some piece of 
gear, usually an SMPS, receives our fundamental, generates the harmonic, 
and re-radiates it.  During CQP two weeks ago, we thought we were in the 
middle of nowhere (a remote mountain ridge in the Sierra), but then saw 
a cell tower a half mile or so away.  My experience  has been lots of 
noise sources at these sites, and something(s) near us were generating 
lots of harmonics.

Last week I was working the Makrothen RTTY contest at home, running 
about 1 kW between 20and 40 with antennas whose feedpoints are 5-10 ft 
apart. Usually that's not a problem, thanks to double stubs on the 40M 
antenna, but that day I heard lots of passive intermod and saw it on the 
P3. Then at some time in the morning the intermod disappeared. I'm 
guessing that the offending device was moved, turned off, disconnected?



On 10/21/2017 9:51 AM, Bob McGraw K4TAX wrote:
> One thing observed at our repeater location is that the CFL was quiet until the the transmitter was on the air. It then generated noise.  In a simplex condition it wouldn't be observed. But in a duplex operation or multiple receiver situation it becomes an issue.  Replaced by a LED with lessened issues.

http://k9yc.com/KillingRXNoiseVisalia.pdf

http://k9yc.com/KillingReceiveNoise.pdf

73, Jim K9YC

On 10/21/2017 9:21 AM, Jim - N4ST wrote:
> I have noticed the background noise level growing on the HF bands, and for me, especially on 18 Mhz.  I need to declare war on RFI and find out what is causing this.  I did carefully checkout some Walmart "100 W" LED lights before committing to them and they were fine.