Hello,
I am facing an RF interference problem involving two completely independent wireless systems operating at 433.92 MHz.

System 1:
- Wireless sensor network
- Sensor nodes communicate with an LCU
- Frequency: 433.92 MHz

System 2:
- Independent third-party transmitter/receiver system
- Frequency: 433.92 MHz

Both systems use different:
- RF modules
- Modulation
- Data rates
- Packet formats
- Protocols
- Addressing
- Firmware

There is no communication relationship between the two systems.

Observed behavior:
1. Both systems work normally when operated independently.
2. When brought close together, communication starts degrading.
3. When both systems transmit simultaneously, packet reception becomes unreliable.
4. If System 1 has higher TX power than System 2, System 2's receiver may fail to receive packets from its own transmitter.
5. Even if System 1 has higher TX power, if System 2 has two transmitters operating, System 1 can also experience packet loss/degradation.

My questions are:

1. What is the main RF mechanism causing this?
2. Is this co-channel interference, receiver blocking, desensitization, near-far effect, receiver saturation, or something else?
3. Why can different modulation/protocol systems still interfere when operating at the same 433.92 MHz frequency?
4. What practical RF/hardware/firmware techniques can be used to allow these independent systems to operate close to each other reliably?
5. Is it possible to solve this without changing the 433.92 MHz operating frequency?

Any technical explanation, practical experience, application notes, or references would be appreciated.

Thank you.

 

If both signals are narrowband, then they will strongly interfere. Effectively, each is acting like a barrage jammer.

Imagine that there is an AM and and FM transmitter that are transmitting on the same frequency. Now imagine that, at a point where the power from each is comparable, we place two receivers, one for each signal. Both signals will be heavily degraded, though the FM signal will suffer less than the AM signal (which will almost certainly be completely unintelligible) with comparable power.

The general solution is to use some form of spread spectrum so that the effective noise presented by the "wrong" transmitter appears as very low noise when the received signal is despread.

 

As WBahn mentioned, both transmitter signals will interfere, if the transmitters are nearby. Even if both signals are not modulated, there will be a beat frequency in the superimposed RF carriers ot the two transmitters which looks like a kind of AM. The reason is: None of the transmitters has a frequency of 433.92000000000000000 MHz, they will have a difference of some kHz in their carrier frequencies and the addition of both signals is an RF signal with an amplitude changing with the difference of the two carrier frequencies.

Therfore you have two possible solutions:

1. If possible, have enough distance between your transmission systems so that they don't interfere each other.
2. The 433 MHz frequency band might have different frequency channels, which are allowed for sending. This depends on the country you live in. Try to change the frequency of one of your systems to another channel, so they can't interfere anymore

 

Welcome to AAC.

The systems probably use either ASK (Amplitude Shift Keying) or FSK (Frequency Shift Keying). When there is another signal on the same frequency from nearly to greater field strength, it is impossible for the receiver to distinguish the encoded data in either of those schemes.

If a signal is much weaker, the interference will be overwhelmed by the desired signal but when the signals are similar or one is greater it will simply garble the encoding. There is nothing you can do abut this with such simple modulation schemes.

Spread Spectrum techniques can solve this problem but the devices that use it are going to be more expensive.

 

Hello,
I am facing an RF interference problem involving two completely independent wireless systems operating at 433.92 MHz.

System 1:
- Wireless sensor network
- Sensor nodes communicate with an LCU
- Frequency: 433.92 MHz

System 2:
- Independent third-party transmitter/receiver system
- Frequency: 433.92 MHz

Both systems use different:
- RF modules
- Modulation
- Data rates
- Packet formats
- Protocols
- Addressing
- Firmware

There is no communication relationship between the two systems.

Observed behavior:
1. Both systems work normally when operated independently.
2. When brought close together, communication starts degrading.
3. When both systems transmit simultaneously, packet reception becomes unreliable.
4. If System 1 has higher TX power than System 2, System 2's receiver may fail to receive packets from its own transmitter.
5. Even if System 1 has higher TX power, if System 2 has two transmitters operating, System 1 can also experience packet loss/degradation.

My questions are:

1. What is the main RF mechanism causing this?
2. Is this co-channel interference, receiver blocking, desensitization, near-far effect, receiver saturation, or something else?
3. Why can different modulation/protocol systems still interfere when operating at the same 433.92 MHz frequency?
4. What practical RF/hardware/firmware techniques can be used to allow these independent systems to operate close to each other reliably?
5. Is it possible to solve this without changing the 433.92 MHz operating frequency?

Any technical explanation, practical experience, application notes, or references would be appreciated.

Thank you.

This is asking for trouble, two RF transmitters on the very same frequency? why would you expect no interference? Just adjust one of them to use a different frequency.

Do you know the type of modulation each device uses?