Military ELMR equipment is authorized for 380-399.9 MHz.
Garage door openers that operate low power unauthorized in the same band are
sometimes messed up.

Wonder if the military or the garage door opener company will win...

http://www.theday.com/article/201207...307239975/1018

On Mon, 23 Jul 2012 09:43:10 -0700, "Wayne"
wrote:

Military ELMR equipment is authorized for 380-399.9 MHz.
Garage door openers that operate low power unauthorized in the same band are
sometimes messed up.

Wonder if the military or the garage door opener company will win...

http://www.theday.com/article/201207...307239975/1018

Reminds me of the garage door hack.

At midnight, from a nearby hill, where you can oversee the whole city,
transmit with a few hundered watts all the door opener codes
in sequence. Use a software to feed the signals.

But even worse and the utmost of all evils, is the Dildo Hack.
You know they have remote controls also.
Every light that comes on in the city after your transmission,
is a feedback of success.


w.

On Mon, 23 Jul 2012 09:43:10 -0700, "Wayne"
wrote:

Military ELMR equipment is authorized for 380-399.9 MHz.
Garage door openers that operate low power unauthorized in the same band are
sometimes messed up.

Wonder if the military or the garage door opener company will win...

http://www.theday.com/article/201207...307239975/1018

It's not exactly ELMR but rather LMRS (Land Mobile Radio System) at
380-400MHz interfering with garage door openers on 315 MHz through
receiver blocking (overload):
http://en.wikipedia.org/wiki/Land_Mobile_Radio_System
This has been a known problem for at least 8 years, yet the garage
door manufactories haven't done anything in the way of improved
receivers. I guess a cheap bandpass filter and some shielding would
be too much for the cost concious garage door opener manufacturers.

Drivel: One of my customers was having problems with their garage
door opener. They said they could easily close the door from the end
of the driveway, but could not open it again from the same location.
When I arrived, I found that they had an aluminum garage door, with
the receiver mounted behind the door. Between the metal door and
aluminium foil backed insulation in the walls and roof, the garage
made an effective screen room. I moved the recevier and wire antenna
to a better location, which fixed the problem.

More drivel: Many years ago, I helped setup a 30 watt Mitrek 440MHz
portable repeater for an event. Since it used mechanical T/R relays,
the dropout time was set rather long to minimize contact cycling.
During the event, we had some traffic from drivers in the nearby
parking lot about being unable to operate wireless car alarms. Oops.
I turned down the TX power which allowed the alarms to operate
normally. Years, they switched to VHF, which stopped blocking the car
alarm receivers, and introduced triggering the car alarms.
Lesson learned: Use low tx power in parking lots.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" wrote in message
...

On Mon, 23 Jul 2012 09:43:10 -0700, "Wayne"
wrote:

Military ELMR equipment is authorized for 380-399.9 MHz.
Garage door openers that operate low power unauthorized in the same band
are
sometimes messed up.

Wonder if the military or the garage door opener company will win...

http://www.theday.com/article/201207...307239975/1018

snip

#Drivel: One of my customers was having problems with their garage
#door opener. They said they could easily close the door from the end
#of the driveway, but could not open it again from the same location.
#When I arrived, I found that they had an aluminum garage door, with
#the receiver mounted behind the door. Between the metal door and
#aluminium foil backed insulation in the walls and roof, the garage
#made an effective screen room. I moved the recevier and wire antenna
#to a better location, which fixed the problem.


snip--
#Jeff Liebermann
#150 Felker St #D http://www.LearnByDestroying.com
#Santa Cruz CA 95060 http://802.11junk.com
#Skype: JeffLiebermann AE6KS 831-336-2558

My own situation was that the remotes in the cars lost range. You could
open the door if the car was practically touching the door, but not much
farther back.

Using various test gear, I found an interfering signal that was just a few
feet away. The remote opener screwed on the outer wall had failed in the
"on" position and was closer to the receiving antenna than the openers in
the cars.

The Genie engineers were quite interested in getting that failed remote in
their hands to examine the problem. They were amazed that I located the
problem, but it's all in the test gear.

Wayne
W5GIE (exiled to W6)

On Mon, 23 Jul 2012 15:12:53 -0700, "Wayne"
wrote:

My own situation was that the remotes in the cars lost range. You could
open the door if the car was practically touching the door, but not much
farther back.

Using various test gear, I found an interfering signal that was just a few
feet away. The remote opener screwed on the outer wall had failed in the
"on" position and was closer to the receiving antenna than the openers in
the cars.

I've seen something like that in action. The problem is in the way
the rolling code works and a rather dumb design decision in the remote
key fob:
http://en.wikipedia.org/wiki/Rolling_code
http://www.atmel.com/Images/doc2600.pdf
When you press the key fob button, some remotes just continue to spew
codes like a machine gun. I think (not sure) that my 2001 Subaru key
fob does this. The problem is that the system compares the received
code with up to 256 anticipated codes that the remote might send. The
idea is to catch up in case the key fob was accidentally pressed and
the receiver missed the transmission. However, if you send 256 codes,
the transmitter and receiver go out of sync and must be
re-synchronized. I actually tried it by pressing the button 256 times
and found that I could no longer unlock the car. It is my
understanding that modern chips have a better algorithm that doesn't
have this problem.

When your transmitter in the outer wall stuck on, it probably ran out
of codes fairly quickly. After that, it was no better than a jammer.

The Genie engineers were quite interested in getting that failed remote in
their hands to examine the problem. They were amazed that I located the
problem, but it's all in the test gear.

Nicely done especially since you had no idea what was causing the
problem.

Wayne
W5GIE (exiled to W6)

I live in W6-land and methinks it's is paradise (except for the
government, traffic, taxes, gas prices, etc).

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS