lbenson
Senior Member
I had hoped to use 433mHz modules (from e-madeinchn) to monitor sensors in my house. For test purposes, I have a sender set up which I can activate by pressing a button. It sends a few characters. My receiver feeds into hserin on a 28X1. My problem is that someone somewhere seems to be transmitting continuously on the 433 frequency, in violation of the three-seconds-per-hour rule. How can I go about locating this transmitter? I am in a row house in an urban environment.
I have womai’s picaxe oscilloscope. When I set it up, with a one-millisecond per division display, and put the first probe on the input to the transmitter and the second on the output of the receiver, I can capture a snapshot of the serial transmissions, and the signals are essentially identical. This snapshot is triggered by a low-going transmission when I press the button on the transmitting module (which is a 14M which reads two DS18B20s and monitors its battery level). When the scope is free-running, my transmitter signal is flat, but there is continuous activity on the receiver—a little noise but mostly 3-volt transitions taking maybe an eighth of a millisecond or less, with the highs and lows held from a quarter of a millisecond to 4 milliseconds or more.
In other words, it looks to my inexperienced eye like a meaningful signal. I when look at my transmissions using sertxd I can see some of the characters which I am transmitting, but it is swamped by the garbage. I tried various settings with hsersetup to see if it was ASCII at another baud rate, but had no luck. It doesn’t look like the ASCII I am sending, even if stretched.
My ultimate use for this is in a rural location where there is not likely to be interference, but I won’t be able to test if I can’t get a good signal. What would I need to try to locate this apparently illegal transmitter. Of course, it could be multiple transmitters.
The attachments show the schematics of my transmitter and receiver modules, but the problem I have is continuous activity on the 433 frequency.
I have womai’s picaxe oscilloscope. When I set it up, with a one-millisecond per division display, and put the first probe on the input to the transmitter and the second on the output of the receiver, I can capture a snapshot of the serial transmissions, and the signals are essentially identical. This snapshot is triggered by a low-going transmission when I press the button on the transmitting module (which is a 14M which reads two DS18B20s and monitors its battery level). When the scope is free-running, my transmitter signal is flat, but there is continuous activity on the receiver—a little noise but mostly 3-volt transitions taking maybe an eighth of a millisecond or less, with the highs and lows held from a quarter of a millisecond to 4 milliseconds or more.
In other words, it looks to my inexperienced eye like a meaningful signal. I when look at my transmissions using sertxd I can see some of the characters which I am transmitting, but it is swamped by the garbage. I tried various settings with hsersetup to see if it was ASCII at another baud rate, but had no luck. It doesn’t look like the ASCII I am sending, even if stretched.
My ultimate use for this is in a rural location where there is not likely to be interference, but I won’t be able to test if I can’t get a good signal. What would I need to try to locate this apparently illegal transmitter. Of course, it could be multiple transmitters.
The attachments show the schematics of my transmitter and receiver modules, but the problem I have is continuous activity on the 433 frequency.
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