Filter binary datagram

The Filter binary datagrams contains filter coefficients used for filtering the received signal. The number of Filter datagrams depends on the number of filter stages in the transceiver.

EK80 systems with the Wide Band Transceiver (WBT) (and similar) have two Filter datagrams.The first datagram contains the filter parameters from the transceiver, while the second datagram contains the filter parameters from the EK80 program. The two filter datagrams have the same structure. They are referred to as "Stage 1" and "Stage 2".

Installed General Purpose Transceiver (GPT) do not have Filter datagrams.

Note

For EC150–3C ADCP there will be one separate datagram for each of the ADCP beams. These are named beam0, beam1, beam2, beam3. Do not interpret these as single beam echo sounder datagrams.

Format

struct FilterDatagram
	{
	DatagramHeaderDgHeader;
	short Stage;
	char Spare[2];
	char FilterType;
	char ChannelID[128];
	short NoOfCoefficients;
	short DecimationFactor;
	float Coefficients[];
	};

Description

•

DatagramHeaderDgHeader: This is the binary datagram in use. The type is FIL1.

•

Stage: The is the filter stage number.

•

Spare[2]: This is a parameter for future expansions

•

FilterType: The is the type of filter.

–

FilterTypeLowNoise = 0

–

FilterTypeLowResolution = 1

–

FilterTypeStandardResolution = 2

–

FilterTypeHighResolution = 3

–

FilterTypeFullResolution = 4

–

FilterTypeHydrophone = 5

–

FilterTypeHighResolutionReducedAttenuation = 6

•

ChannelID[128]: This is the channel identification.

•

NoOfCoefficients: This is the number of complex filter coefficients.

The filter coefficients in the Filter datagrams are used in combination with information of the transmitted signal to create the matched filter which can be used to create matched filter or pulse compressed echogram data. The filter coefficients are complex values.

Thus, the number of values found in Coefficients[] are 2 x NoOfCoefficients since each complex filter coefficient consist of one real part and one imaginary part. The complex filter coefficients F(n) are arranged in Coefficients[] as:

real(F(1)), imag(F(1)), real(F(2)), imag(F(2)), …. ,

•

DecimationFactor: This is the filter decimation factor.

•

Coefficients[]: These are the filter coefficients.

Record of changes

1.23: No changes made

1.22: No changes made

1.21: Added:: FilterType

1.20: No changes made