DHY-03 User Handbook
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internally generate a 31 frequency multi-tone signal to cover the full range of the telephone
bandwidth. The echo signal is monitored and the parameter sets with the lowest return
signal are saved to the flash memory.
Calibration of Telephone Interface
The telephone interface chipset contains a simple impedance matching a short-term echo
cancellation algorithm. The DHY-03 can tune the parameters for these routines at 2 levels:
- full calibration involves checking the return signal for all possible values of AC impedance
and for all sets of the hybrid parameters; local calibration doesn’t change the AC impedance
and just checks the return signal for the associated set of hybrid parameters. Calibrating the
telephone interface parameters will make the current network coefficients invalid so the
DHY-03 will perform a network cancellation coefficients calibration.
Calibration of Network Cancellation Coefficients
The DHY-03 will generate a 31 frequency multi-tone signal to cover the full range of the
telephone bandwidth and this will be sent to the line in a 2 second on, ½ second off
cadence. The full network cancellation algorithm will run to determine the optimum
coefficients and these will be saved to flash memory and be used as the starting point
whenever the DHY-03 is powered up. These coefficients are only valid for the conditions
present during the calibration and will be cleared if the country code or network
cancellation duration is changed.
Acoustic Cancellation
In addition to echo cancellation across the network the DHY-03 is able to perform local
acoustic echo cancellation. This is used when there is feedback from the audio output to
the audio input usually due to the output being sent to speakers and being picked up
by a microphone input. The effect of this is that callers will hear themselves in echo and
could make a conversation untenable. The DHY-03 is able to perform an echo cancellation
algorithm on the return signal and subtract the content due to the original caller from
the signal sent to the line. This algorithm has a fixed TAP duration of 16ms and due to the
variable nature of the echo is optimised for a softer dynamic response.
Updating Firmware
The DHY-03 operating software is stored in flash memory and can be overwritten as
new code is published. The flash memory is partitioned into boot code, firmware, and
saved parameters. Only the firmware partitions are erased so that even in the unlikely
occurrence of a power fail during the flash update the system can still be recovered.
The preferable method of communicating with the DHY-03 is to use the SCI utility provided
free from our web site. However it is possible to use Hyperterminal – the standard windows
communication package. Set the comms port to 19200, e, 8, 1 with Xon/Xoff protocol and
start the DHY-03 in bootstrap mode by powering up with the line connect Button held
down for 10 seconds. Once the communication link has been established send a DWN:
command and then use the Transfer->Send Text File to send the new bootstrap code.
The DHY-03 will reboot when the file transfer is complete.
CONFIGURATION & CONTROLS
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