What's wrong with
SAME / EAS technology?
Both FCC and NWS have stated that they chose non-standard specifications
for security reasons.
The use of non-standard specifications provides no real security.
In fact it makes transmission easy and reception difficult!
It uses a non-standard bit transmission rate of 520.83 bits per second.
Non-standard tone frequencies of 1562.5 Hz (Logic 0) and 2083.3 Hz (Logic
Synchronous timing. (No bit clock is included in burst)
No positive error checking such as CRC.
No marker at end of burst.
Time diversity is provided by sending the message three times. You
still cannot guarantee that the received message is correct without a valid
CRC. This is especially true for clock timing errors.
If they had used standard technology it would have been much more reliable
and easier to implement! Technology such as packet radio (developed
by ham operators) is widely available, highly reliable, and cheap to implement.
Oh well, it must have been designed by a committee!
In this day in age anyone with a computer can generate these messages.
Actually, generating the messages is much easier than receiving them!
The tones can be produced from a 1 MHz crystal with a programmable divider
chip. (divisors are 480 or 640 for the tones and 1920 for the bit clock)
A simple computer program or $5.00 microprocessor or PIC chip can provide
the whole circuit.
Reception of the bursts is much more difficult than transmission.
Does this make any sense?
by: Richard D. Burgan