Dear Matthew and Pishan,
I looked at the signal from channel 14 in your archive M1236949301.
There was no signal from No14. You are not receiving bad messages at any
significant rate in your lab. Your interference does not have the
correct modulation frequency to appear like one of our transmitter messages.
For more about bad messages see here:
Instead, the interference in your lab is corrupting messages from the
transmitters. Each transmitter appears to get one corruption every two
seconds on average. Compare this to my basement lab, were I get less
than one corrupted message every hundred seconds. It is possible for our
transmitters to interfere with one another, but unlikely, because we
designed the receiver to be proof against such intereference. The cause
of your corrupted messages is some other source of 900 MHz power. It
could be a 900 MHz cordless phone, some 900 MHz wireless data
acquisition system, or 868 MHz and 940 MHz cell phones.
For more about corrupted messages see here:
To corrupt a message, the interference must corrupt the bit sequence in
the message so that our error-checking is defeated. My guess is that we
are losing a hundred messages for every message that is corrupted but
The system appears to work okay with the antenna centered upon two
cages, but it no longer works with the antenna centered upon the four
I will plan to boost the transmitter power in the next design. A factor
of 10 boost will give a factor of 3 increase in range. If necessary,
I'll design a new receiver that has four independent antenna inputs, and
which receives messages through all antennas, rejecting duplicates and
storing the unique messages in memory.
For now, I sent a new antenna, cable, and a T-junction to Matthew for
Pishan to use as a second antenna. It may be that two antennas each
centered upon two cages will give better performance, even though all
we're doing is combining the signals at the receiver. When I try the
same arrangement in my lab, I don't get much improvement, but I don't
see any loss of performance either, so it does no harm.
There is also the faraday cage option, rejecting interference. Perhaps
we should try that, although it seems a lot of work. We would not have
to reject all interference power, only 90% of it.