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.
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to arch...@mail-archive.com
