On 8/29/2011 8:48 PM, The Daring Dufas wrote:
On 8/29/2011 3:01 PM, Robert Green wrote:
"The Daring wrote in message
...

stuff snipped


Back in the late 1980's I was working and living in the country of
Californiastan when the community I was in at the time started having
problems with their electric garage doors opening and closing as if
possessed by some evil door opener. It turned out that the US Navy
was testing the big search radars on some ships in the bay. Those big
powerful radars were producing an RF harmonic signal that was just right
to screw with the RF remote controls for a lot of openers. :-)

Yes, I was aware of them. Lutron's Radio RA system had to add a second RF
channel in NYC because of interference from a source that wasn't going
away.
Read: government.

We just had a round of that a few years ago near DC at Andrews AFB and
others in Denver had the same problem. I know that two military research
labs nearby (I live between the two on almost a perfect straight line are
tasked with IED jammer development so I wouldn't be surprised if the
signal
correlated with elevated threat levels. The DC area is as the Pentagon
says
"target rich environment."

But in reality I think Dave is probably onto the real source: The local
power company has just instituted a program where they hook a
receiver/relay
between your AC and the powerline. In brownouts, they can shut your AC
off
remotely. I was going to apply for it because we don't use our CAC
anymore
and have switched to window ACs, but that seemed to be cheating so I
decided
not to.

The "blips" started appearing a month or two ago, when summer began. They
are not there today, with the temps in the cool, dry 70's (the benefit
of a
hurricane - wonderful, cool, clean air for a day or afterwards). Now I
have
to download some temperature data and try to correlate that with the
times
the bogies appear in my Homevision log file (records all externally
generated commands to log file). The days of endless bogies generate huge
log files, 100 to 1000 times the normal size.

--
Bobby G.


I'm an old broadcast engineer/two way radio tech and I had to track down
RF interference all the time. My friend who worked for the local
power company as an electrical engineer in charge of their
communications told me that back in the 1970's they were tracking down
a lot of RF interference caused by doorbell transformers. I have an
idea that today's proliferation of "Wall Warts" could be responsible
for a lot of RF and power line borne interference. It's something to
consider.


Doorbell transformers sound really bizarre as a source of RF. Somebody
at a.h.r tracked down a source that says it is from contacts that
disconnect the transformer when the current is too high for a class 2
(limited energy) transformer. (Or something like that.) Contacts would
repeatedly open (with arcing) and close.

My guess is that class 2 AC-out wall warts are "impedance protected",
which most doorbell transformers probably are now. At too high a current
the voltage just droops.

My guess is that DC wall warts are the same, or the DC side has a
current limit circuit. Are they switch-mode these days? Wouldn't think
switch-mode would be worse than other switch-mode power supplies found
all over the place.