MFJ 226 - User Manual

The MFJ-226 is a compact, single-port Vector Network Analyzer (VNA) designed for characterizing complex RF loads in 50-Ohm systems with high accuracy. It is part of the Times Technology Series of analyzers and is packaged for portable use, offering advanced features typically found in more expensive units.

Function Description:

The MFJ-226 functions as a graphical antenna impedance analyzer, capable of measuring and displaying various RF parameters. It operates by generating a test signal through a directional coupler to the load under test. Any impedance mismatch causes a portion of the signal to be reflected back. The directional coupler measures the amplitude and phase of both forward and reflected signals, feeding this data to a microprocessor. The microprocessor then converts this data into useful engineering parameters such as SWR, complex impedance, and S11 coordinates, which are displayed on the LCD screen.

The analyzer supports two primary operating modes:

Single-Frequency Mode: In this mode, the MFJ-226 presents SWR, complex impedance (series and parallel), and S11 scattering parameters (rectangular and polar). SWR readings are displayed in large, easy-to-read numbers, complemented by a bargraph for visual representation. The DDS generator can be set to a desired test frequency either by direct keypad entry or by scroll/step tuning using the up/down arrows. This mode includes several screens:
- SWR, Frequency: Displays SWR and frequency, with SWR in large numerals and a bargraph.
- SWR Z R X Display: Shows SWR in smaller characters along with the Z, R, and X values of the load.
- Series Impedance: Displays the load's resistive and reactive components as two discrete elements connected in series, including true reactance sign and inductive/capacitive value at the test frequency.
- Parallel Impedance: Displays resistive and reactive components as two parallel elements, including true reactance sign and inductive/capacitive value.
- S11 Scattering Parameters: Shows both Rectangular and Polar S11 representations of the load.
Swept-Frequency Mode: This mode graphically plots seven test parameters over a user-selected frequency span. It allows for local calibration to ensure accuracy through transmission lines. The parameters plotted include:
- Standing Wave Ratio (SWR)
- Impedance Magnitude (Z)
- Resistance (R)
- Reactance (-X or +X)
- Return Loss (RL, S11)
- Phase Angle (Deg)
- Smith Chart A tunable marker is available in this mode to pull up precise alphanumeric data for any point along the X-axis of the plot. Setup involves defining start and stop frequencies and Y-scale settings.

Important Technical Specifications:

Frequency Range: Continuous, 1 MHz to 230 MHz
Frequency Resolution: 1 Hz
Test Port Termination: Type-N Female
Output Power: +10 dBm typical
Harmonics: -15 dBc typical
LCD Display: 128 x 64 resolution with backlight
Dimensions: 6.5" (165 mm) x 3.12" (80 mm) x 1.25" (32 mm)
Weight: 10 oz with batteries and UHF adapter
Power: Two (2) AA cells, Alkaline or NiMH (external charger required for NiMH)
Computer Interface: USB serial
OSL Calibration: Male-N or UHF, Open, Short, and 50-Ohm Load

Usage Features:

OSL Calibration: The MFJ-226 supports Open/Short/Load (OSL) calibration for both Global Calibration (covering the entire 1-230 MHz span) and Local Calibration (for specific swept-frequency measurements through test cables or transmission lines). This feature compensates for phase rotation and losses in feedlines and test cables, ensuring accurate measurements. The analyzer is factory-calibrated and typically does not require recalibration for initial use.
True Reactance Sign: It calculates the true reactance sign (plus or minus), eliminating sign ambiguity.
Continuous Frequency Coverage: The DDS stimulus generator provides continuous coverage from 1 MHz to 230 MHz.
Direct Frequency Entry & Step-Tuning: The DDS accepts both step-tuning and direct-frequency entry via the keypad, offering flexibility in setting test frequencies.
Memory Files: The device includes 32 memory files for capturing and downloading test data to a PC, and four additional memory files for storing calibration setups.
Backlit LCD Display & Keypad: All test results are displayed on a bright, easy-to-read backlit LCD. The deluxe backlit keypad features large, positive-action keys for easy field operation.
Rugged Design: The analyzer is housed in a thick-wall molded case that is hand-contoured and rugged.
PC Control: A PC host program is available for controlling the analyzer and displaying measured data. The program allows for setting START and STOP frequencies, choosing display modes, and adjusting the scale. Data can be saved in CSV format and loaded from the analyzer. Manual control via computer is also possible for custom data capture and control routines.
Menu Structure: The MFJ-226 features short, circular menus (Main Menu and five Sub-Menus) for quick and easy access to all functions.
Settings Mode: This mode allows users to check and change default settings such as backlight behavior (Auto, On, Off), auto power off (Enabled/Disabled), battery type (Alkaline/NiMH) for low-battery warning, step size unit (1MHz to 1Hz), LCD contrast, and calibration data protection (Lock/Unlock Cal Data). It also provides system information like model number, firmware version, and battery status.

Maintenance Features:

Firmware Updates: MFJ provides access to firmware updates, which can be performed via the USB interface. The procedure involves installing fresh batteries, downloading the firmware update program and file, entering update mode on the analyzer, connecting to a PC, and executing a command line instruction.
Battery Management: The analyzer uses two AA batteries (Alkaline or NiMH). It includes a built-in battery indicator that can be set for the type of battery in use. To extend battery life, it is recommended to set the backlight to AUTO and auto power off to ENABLE in the SETTINGS Menu.
Calibration Data Protection: The "Cal Data Protect" feature in the Settings menu locks global calibration data to prevent accidental erasure, which is important as the unit is factory-calibrated. Unlocking is only recommended for performing a global recalibration.
Display Protection: The display window comes with a plastic film from the factory to protect it from scratches during manufacturing, which can be removed if desired.