datarate in 345mhz band
Thank you!(urgency!)
Do you have a name of the manufacturer of the system?
a alarm guard system, its operating frequency usually is 345MHz in USA, I only want to know how to test its RF feature, because I haven't the documents about it now, I want to get USA or ETSI spec to reference.
Thank you very much!
It is most likely a pulse amplitude modulated system. That is, it is a crystal oscillator whose DC power is switched on and off to send data. The most common method is the vary the duty cycle, so a "1" is 2/3 of a data rate period, and a "0" is 1/3 of a data rate period.
You test it by having an antenna and a diode detector feeding a digital oscilloscope. When a short burst of data happens, it triggers the scope and you can scroll back and read the data.
Do not get your receiving antenna too close to the transmitter, or leave any big pieces of metal near the transmitter, when testing. 1 foot away should be far enough. Getting too close might influence the oscillator power and turn on/turn off time, and you will get an erroneous response. This is because the antenna loop is often an important part of the oscillator circuit, so loading the loop is like changing the inductor in a Hartley crystal oscillator.
Thank you everybody, These tips are very helpful for me.
I also have a question, how to test the sensitivity of this system?
For example, a communication system, we can use signal generator and error bit meter to buildup a test system to compare error bit radio. but I don't know how to buildup test system for this system.
if I test sensitivity of mobilephone, I can use the special device such as CMU200, whether have such device in entrance guard industry?
pls tell me, thank you very much!