Hi everybod,
I want to read and send 40.6835MHz signals with an Arduino. Has someone done it before?
My first idea was to buy a send receive kit for 433MHz and switch the crystal to a 40.6835 one on the sending unit. Do you think that's possible? The second problem is then, how to receive the packages.
Any ideas?
Possible, but it probably won't work.
Why do you want to send on that frequency? Is it legal to do so in your country?
RF circuits use a thing called a tank. a tank passes a certain frequency and eliminates all others. a tank is composed of a coil and a capacitor.
changing the crystal will just move your RF oscillator to a frequency rejected by the tank
I want to read and send 40.6835MHz signals with an Arduino. Has someone done it before?
No. That is a really odd frequency.
My first idea was to buy a send receive kit for 433MHz and switch the crystal to a 40.6835 one on the sending unit. Do you think that's possible?
No. The other component values you will have to use ensures that you will need a total redesign. And some expensive test kit to test it.
The only thing I know of operating around that frequency is Radio Control in some countries (including the UK for surface models only). But whatever it is you're doing you're going to need to know a lot more about the RF signal than just the carrier frequency.
Steve
In short you need to purchase the ready-built transmitter for that frequency. This has little or nothing to do with an Arduino but should be self-evident.
Yet another example of the simple-minded "you can do anything with an Arduino" meme. Too much time spent on "instructables" perhaps? 
quiddi:
Hi everybod,I want to read and send 40.6835MHz signals with an Arduino. Has someone done it before?
Do you mean 40.685MHz garage door opener? If so get a garage door sender and receiver
and hack into them?
My first idea was to buy a send receive kit for 433MHz and switch the crystal to a 40.6835 one on the sending unit. Do you think that's possible?
Not in the slightest, completely different band, radio circuits are narrow-band tuned circuits that have a
small amount of frequency flexibility only. Not to mention the SAW filter.
The second problem is then, how to receive the packages.
Any ideas?
There's always SDR of course...