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Re: [Discuss-gnuradio] Car alarms and garage door openers

From: Johnathan Corgan
Subject: Re: [Discuss-gnuradio] Car alarms and garage door openers
Date: Tue, 06 Jun 2006 13:03:22 -0700
User-agent: Thunderbird (X11/20060522)

Michael Milner wrote:

> I just took a look at my car's keyfob with the USRP RFX400 board (it seems
> to transmit around 433.923MHz.  It is using FSK modulation, a few tens of
> kilohertz deviation.  It demodulates pretty well, but the centre frequency
> isn't very stable (Is there any way to automatically detect the centre
> frequency within a range?)
> Just eyeballing the data with the scope, it seems to change with every
> keypress.  It's hard to really see what the data is.  Is there anything in
> GnuRadio that will let me measure the pulse widths?

I looked up the FCC ID for mine.  It's allocated for use between 314.5
and 315.5 MHz, which is I'm sure to allow cheap oscillators to be used.

Found it with the TVRX at 314.875 MHz.  Looks like OOK with a minimum
pulse width of 250us.  Like yours the sequence seems to change with each
key press.  See attached JPEG.

-Johnathan, AE6HO

JPEG image

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