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I have this 433 mhz transmitter and receiver for arduino. enter image description here

I want to replay my garage door remote control with this transmitter so I reversed the RC (remote control) signal with RTL-SDR/sdrsharp and audacity. It is not working.

enter image description here

Why is there a shift between the carrier frequency of the signal transmitted with arduino (RH_ASK library) and my garage door RC ?

How can I change this ?

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  • the remote control could be using encrypted communication ... if it does, then replaying the code will not work .... compare multiple recordings before wasting your time trying to retune the transmitter
    – jsotola
    Jan 11, 2021 at 23:07
  • Yes I checked it, the code is not changing over time.
    – Melfos
    Jan 12, 2021 at 6:51
  • I'm more worried about difference in duration of the signal than the 0.1Mhz difference in frequency. (Though, if you bought a tree-pack, like in the image, you could try the other two. )
    – Gerben
    Jan 12, 2021 at 14:30

3 Answers 3

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The reason is that your garage door opening is operating on a different carrier frequency than your transmitter module. The plot you are showing is called a "waterfall" plot and shows the frequency on the "x" axis with time progressing from top-to-bottom.

The garage door remote appears to be centered just above 433.900 MHz while your transmitter is around 434.000 MHz. While that might not seem like a large difference, these things are designed to be receptive in a very narrow band.

So you need to read the specifications of your transmitter module and see if its frequency is adjustable and, if so, adjust it upward to the correct frequency.

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Are you certain about what modulation is used by your garage door?
There are relatively strong side bands on 433.800 MHz. While most of the signal is at 433.900 MHz this might be an FSK variant instead of ASK modulated signal. In that case you will not be able to use this transmitter for your task. Usually taking apart your remote and searching for the IC numbers will give you more insight about what is being used. If you find an FCC-ID on your remote, you can try to find information that way as well.

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    All the garage door systems I have seen for many years use a KeeLoq encoder to prevent exactly what you are doing from working. The code changes every time it is used. There is a lot of stuff on the internet on KeeLoq that may help you. The Microchip HCS301 was once the most widely used system on garage and gate remote control and receivers. The chip uses the KeeLoq algorithm. The HCS301 KeeLoq system transmits 66 data bits.
    – Gil
    Jan 13, 2021 at 21:32
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The term "433MHz" refers not to a frequency, but to a band. That is, a range of frequencies, officially defined as 433.05MHz to 434.79MHz. You are free to use any frequency within that range you choose for your carrier frequency. The manufacturers of the garage door opener have chosen one frequency, your TX/RX are tuned to another frequency.

If you want to receive the frequency your opener transmits at then you will need a receiver tuned to that exact frequency. If you want your garage door to receive your signals then you will need a transmitter tuned to the correct exact frequency.

You can think of it as a normal radio. "433MHz" is akin to "The FM band". Within that band are a number of stations, all with their own frequency. Your TX/RX pair are tuned to BBC Radio 2, but the garage door is working on Classic FM (replace with two radio stations that mean something to you...)

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