I am using an RFM69HW board containing a Semtech SX1231H packet radio unit. It will soon transmit data from my aquarium controller.
I am using the 433 MHz band. I saw that when I sent full effect (100 mW at +20 dBm) and sent 5 timer per second at 433.92 MHz my car key system halted, meaning the car would not open or lock. 10 meters through wooden walls. I opened the key and saw that it sent at the same mid-in-band 433.92 MHz. When I changed to down 1/10 of the band at 433.706 MHz the situation was better: the car opened and closed after a button press or two. If I sent once per second then even 433.92 MHz did not seem to disturb the car key system noticeably.
The RFM69HW uses data packets (with preamble etc.) at a certain baud rate and CRC16 plus I use a CRC32 in my payload. Sending at 433.92 MHz and listening with another board 15 cm away at 433.706 MHz gave no messages coming through, as expected.
However, my car key system [1] seems to be much less advanced. Of course it could not be expected to necessarily get through at the same frequency if that frequency was jammed, but it never really came to that I would think.
How does such a car key system work? Is what I see according to expectations?
Observe that my packets, even if they hindered the car from being opened, never opened it!
My car is a 2012 model bought in 2011, but I guess the key system is from the original version of that car series, coming in 2005. It's a German make.
I am blogging about these matters. See [2] with disclaimer.
[1] https://fccid.io/MQU-B3333D
[2] http://www.teigfam.net/oyvind/home/...gh-the-shelf/#frequency_crash_with_my_car_key - disclaimer: no ads, no money, no gifts, just fun and expenses!
I am using the 433 MHz band. I saw that when I sent full effect (100 mW at +20 dBm) and sent 5 timer per second at 433.92 MHz my car key system halted, meaning the car would not open or lock. 10 meters through wooden walls. I opened the key and saw that it sent at the same mid-in-band 433.92 MHz. When I changed to down 1/10 of the band at 433.706 MHz the situation was better: the car opened and closed after a button press or two. If I sent once per second then even 433.92 MHz did not seem to disturb the car key system noticeably.
The RFM69HW uses data packets (with preamble etc.) at a certain baud rate and CRC16 plus I use a CRC32 in my payload. Sending at 433.92 MHz and listening with another board 15 cm away at 433.706 MHz gave no messages coming through, as expected.
However, my car key system [1] seems to be much less advanced. Of course it could not be expected to necessarily get through at the same frequency if that frequency was jammed, but it never really came to that I would think.
How does such a car key system work? Is what I see according to expectations?
Observe that my packets, even if they hindered the car from being opened, never opened it!
My car is a 2012 model bought in 2011, but I guess the key system is from the original version of that car series, coming in 2005. It's a German make.
I am blogging about these matters. See [2] with disclaimer.
[1] https://fccid.io/MQU-B3333D
[2] http://www.teigfam.net/oyvind/home/...gh-the-shelf/#frequency_crash_with_my_car_key - disclaimer: no ads, no money, no gifts, just fun and expenses!