Re: garage remote jamming

[nobody@xxxxxxxxxxxx (Dave Houston)]

"Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote:

>So I cranked up Google to search for "RadioRA NYC problems" and that led to
>another document at:
>
>http://www.radiora.biz/technical_info/pdf/RFwhitepaper.pdf.
>
>That described how, in 1999, they added a second frequency to their RadioRA
>equipment.  From the description of techniques they examined and discarded,
>I'm confident that they are not using any spread spectrum encoding
>techniques to transmit their signals.  I'd say we know exactly how they
>intend to deal with any interference on their "A" band at 418MHz.  They say:
>
>**********************************************************
>RadioRA ?B? Frequency 434 MHz ? one channel (AM)
>
>In nearly a decade?and with over 1 million devices sold?only one isolated
>area in North America has interfered with our one channel RadioRA system?New
>York City. The ?B? frequency was developed to address this situation.
>
>**********************************************************
>
>That was in 1999, before the WTC and 9/11 and the tests at Elgin, AFB and
>Quantico, CA so it's hard to say whether the assumptions they made in that
>design whitepaper are still valid.

That's about equal parts puffery and technical and seems to be more their
response to ZigBee than anything else. Their critique of "RF standards" and
mesh networks would apply equally to Z-Wave.

They use 418MHz ASK/OOK which is also used by almost all of the IR extenders
(e.g. Powermid) and most of the RF-capable high-end touchscreen remotes
(e.g. Pronto). In Europe, all of the above as well as several RF based
lights/appliance systems use 433.92MHz (i.e. their "B" frequency) and, if
RadioRA sells in Europe they are also required to use 433.92MHz.

Any nearby ~418MHz transmitter will jam their "A" frequency" and any nearby
~434MHz transmitter will jam their "B" frequency.

In this specific case the military frequency was far enough away from 418MHz
that it was not likely to affect any RadioRA but, in general, their
"immunity" from interference is more a matter of miniscule market share than
technical prowess.

For those who reacted by blaming the garage door makers, a glance at FCC
frequency allocations shows that nearly the entire spectrum allowed for
low-power unlicensed use under FCC Part 15 is also allocated for some type
of licensed use. I doubt there's any easy way to determine what particular
sub-band might avoid some future problem like this - it goes with the
territory.

     http://www.ntia.doc.gov/osmhome/allochrt.pdf
     http://www.panix.com/clay/scanning/frequencies.html


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