Calibration Commands

Commands for performing VNA calibration and managing calibration data.

cal

Perform calibration measurements or control calibration state.

Syntax

cal [operation] [value]

Operations

Operation	Description
`open`	Measure OPEN standard
`short`	Measure SHORT standard
`load`	Measure LOAD standard
`thru`	Measure THRU standard (S21)
`isoln`	Measure isolation (S21)
`done`	Calculate error terms and apply
`reset`	Reset calibration data
`on`	Enable calibration correction
`off`	Disable calibration correction
`data <n>`	Output calibration data for type n

Calibration Types

Index	Type	Standard
0	`CAL_LOAD`	50 ohm load
1	`CAL_OPEN`	Open circuit
2	`CAL_SHORT`	Short circuit
3	`CAL_THRU`	Through connection
4	`CAL_ISOLN`	Isolation

Example Session

ch> sweep 1M 100M 101
ch> cal open
open
ch> cal short
short
ch> cal load
load
ch> cal thru
thru
ch> cal done
done
ch> save 0

Calibration Data Format

ch> cal data 0
0.001234 0.005678
0.001245 0.005689
...

Each line contains real and imaginary parts for one sweep point.

save

Save current calibration and settings to flash memory slot.

Syntax

save <slot>

Parameters

Parameter	Description
`slot`	Calibration slot number (0-4 for F072, 0-6 for F303)

Examples

ch> save 0
ch> save 3

What Gets Saved

The properties_t structure is saved, containing:

Calibration data for all standards
Frequency range (start, stop, points)
Electrical delay settings
S21 offset
Trace configurations
Marker positions
Current calibration slot number
Checksum

Slot Capacity

Target	Slots	Size per Slot
F072	5 (0-4)	0x1800 (6 KB)
F303	7 (0-6)	0x4000 (16 KB)

recall

Load calibration and settings from flash memory slot.

Syntax

recall <slot>

Parameters

Parameter	Description
`slot`	Calibration slot number

Examples

ch> recall 0
ch> recall 3

What Gets Loaded

All data saved by save command:

Calibration coefficients
Sweep settings
Trace/marker configuration

Behavior

If slot contains valid data, loads and applies it
If slot is empty or corrupted, reports error
Triggers sweep restart with loaded settings

Verifying Slot Contents

After recall, use these commands to verify:

ch> sweep
1000000 100000000 101

ch> trace 0
0 1 0 1 1.000000 7.000000

Calibration Data Structures

Error Term Array

Calibration data is stored as complex values per sweep point:

float cal_data[CAL_TYPE_COUNT][SWEEP_POINTS_MAX][2];

Calibration Status

The cal_status byte indicates which calibrations are valid:

Bit	Mask	Calibration
0	0x01	LOAD
1	0x02	OPEN
2	0x04	SHORT
3	0x08	THRU
4	0x10	ISOLN

Full 1-port cal requires bits 0-2 (mask 0x07). Full 2-port cal requires bits 0-4 (mask 0x1F).

Error Term Calculation

When cal done is executed:

Calculates 1-port error terms from OPEN, SHORT, LOAD
Calculates 2-port error terms from THRU, ISOLN (if available)
Sets CALSTAT_APPLY flag to enable correction

Calibration Interpolation

If sweep range differs from calibration range:

RANGE mode ON: Interpolates calibration data
RANGE mode OFF: Uses closest calibration points

Control via menu: CALIBRATE > RANGE

Or via config command:

ch> config range 1

Enhanced Response Calibration

For S21 measurements with limited standards:

Perform THRU measurement only
Calculate response correction

Enable via menu: CALIBRATE > ENHANCED RESPONSE

Non-50 Ohm Systems

If using non-standard load impedance (requires __VNA_Z_RENORMALIZATION__):

ch> config loadr <ohms>

Example for 75 ohm system:

ch> config loadr 75
ch> cal load
... (connect 75 ohm load)

Source Code Reference

Calibration commands in main.c:

cmd_cal: lines 2400-2500
cmd_save: lines 2502-2530
cmd_recall: lines 2532-2570

Calibration math in main.c:

apply_CH0_error_term: lines 900-950
apply_CH1_error_term: lines 952-1000
cal_interpolate: lines 1002-1100