System Overview  |  Schematic  |  PC Board  |  Documentation  |  Software  |  Photos  |  Parts List  |   Assembly Guide  |   Ordering



The Network Analyzer Terminal (NAT) is a handheld graphic display terminal for controlling the "Poor Ham's Scalar Network Analyzer" (PHSNA). 

The NAT provides a convenient alternative user interface for controlling the PHSNA and displaying its graphic plots of Devices Under Test on a small graphic terminal, instead of requiring connection to a PC for the user interface.

As the name implies, the PHSNA is a tool for analyzing the frequency response characteristics of hardware networks such as filters and amplifiers. The NAT firmware has been developed to support and enhance the PHSNA, as documented and discussed in the online Yahoo Group found at:

The NAT handheld terminal may be used with the PHSNA instrument simply by connecting the NAT's serial port into the digital "UART" lines (Rx and Tx signals) of the PHSNA's internal Arduino controller. Commands may then be issued to the PHSNA, and data may be collected from the instrument for display and analysis, similar to the way in which the PHSNA uses the PC for its user interface ... only smaller and easier.

The NAT pcb assembly may also be built into an enclosure containing the PHSNA electronics (Arduino, shield, and power detector), thus creating a completely standalone instrument for the lab bench top.

We hope you all enjoy using the Network Analyzer Terminal!  We usually hang out in the PHSNA Yahoo Group and we'd be happy to answer any questions or field ideas for additional capabilities.

73, George N2APB  &  Dave AD7JT








NOTE ... The SNA Kit is now available!
The NAT has evolved now to become the SNA (Scalar Network Analyzer), providing many
additional capabilities for approximately the same price (plus a DDS-60 siggen card).
If you already have a NAT, you can still manually upgrade it to SNA
by following the information on this NAT website.
New orders should be done at the SNA website.

Version 4: Slide Deck and v4 Extensions
See how version 4 adds SNA (Scalar Network Analyzer) capability!

Version 3 is available
Adds DDS-60 siggen RF output & RF Input.
Read all about the new capabilities here

NEW White PaperSNA Calibration for Use in Your Shack
... Demystifying the approach and benefits of the NAT-SNA Calibration process.


• Handheld graphic terminal for display and control of the PHSNA

• 3.2 inch, 240 x 320, 16-bit color graphic LCD display w/touch panel

• User-friendly operator interface

• Field upgradable firmware

• Serial port connection to PHSNA (digital UART 3.3V)

• Keyboard input for control of SSNA menu system

• 32KB EEPROM for persistent storage of settings and options

• 14 Macros (in EEPROM) for storing operating parameters

• PLX-DAQ (Excel) mode for test automation and PHSNA compatibility

• Compatible with standard and enhanced PHSNA firmware versions

• Simplified calibration (no curve fitting required)

• Measurement & Plot Capabilities (v1.0):

      - Testing and evaluating filters

      - Measuring crystal parameters

      - Return Loss Measurement

      - VSWR and antenna tuning

      - Continuous/repeated operation options

• SD Card mass storage up to 1 GB provides:

      - FAT16 file system compatibility

      - Subdirectory support for easy file management

      - Data spooling and playback

      - Calibration data storage and reloading

      - Direct data exchange with Windows and Linux apps

      - Easy and efficient firmware upgrades

      - DOS–like commands to manage and playback data files



  • PCB: 4.47" x 3.31"

  • Enclosure: 4.82" x 3.77" x 1.39"

  • Data rates: 1.2 to 19.2 kbaud

  • Power: 12V DC @ 120ma (typ) (330ma for NACT with DDS-60)

  • Weight: 7 oz (approx)

System Overview (of the PHSNA instrument + NAT Terminal)

The devices identified in the block diagram below are those used in the PHSNA implementation of the base SSNA instrument.  Other implementations may use other devices and still be compatible with the NAT.  The block labeled "terminal" can be a PC running a terminal emulator program (Terminal mode) or a spreadsheet program (such as Excel) with a special macro or VB add-on that allows the PHSNA firmware to access specific cells in the spreadsheet (PLX mode). The NAT can operate in both of these modes plus two additional modes used to setup operating parameters (Command mode) and manage spooled files (DOS mode). The microcontroller controller used in the PHSNA implementation is an Arduino Uno, coupled with a shield (hardware daughterboard) plugged in on top. The PHSNA firmware running in the Uno commands the signal generator to produce a specific RF sine wave, which is then applied to the input of the device under test (DUT). The output power level of the DUT is measured by the RF power detector, which produces an analog voltage level that is delivered to an ADC input of the UNO. The digitized voltage level is a function of the signal generator output and the frequency response of the DUT. The power detector output is logarithmic and is expressed in dBm relative to the signal generator output. The AD8307 output is calibrated and is extremely accurate. The AD9850/51 output level is not generally linear with respect to frequency and, therefore, it will be necessary to calibrate the PHSNA across the frequency range of interest if accurate readings are desired.

The interface between the Uno and the NAT terminal is a simple digital UART-based serial interface. The Uno’s USB interface is generally used to interface to a PC running a terminal emulator program or custom software with special USB drivers that emulate a serial interface at that end. The USB interface is not used when the PC is replaced by the NAT, which uses the digital RxTx serial interface lines to control the Uno and collect/display its data. All communications between the Uno and the NAT are encoded in ASCII. The NAT terminal supplies operating parameters for instrument operation such as frequency range and frequency increment. The PHSNA firmware commands the signal generator to sweep the RF signal while it records the DUT power output for each frequency step. The digitized power outputs are sent to the terminal for displaying directly as raw data and/or for plotting. Spooled data may also be saved on an SD Card for detailed analysis on another platform.






Download schematic PDF


PC Board

The NAT pcb is a two-layer design (top and bottom traces and ground plane), with plated-through holes and green soldermask.  The board size is 4.46" in length by 3.32" in width.  The QVGA display module plugs into the 2x20 receptacle at the left side by the power regulators.  The assembly requires a minimum of 1.1" depth. The 20-pin DIP integrated circuits are soldered directly to the pc board, while the 28-pin DIP microcontroller is socketed to allow for replacement with another device when newer firmware is made available.  The microcontroller may also be reprogrammed in situ using a suitable programming pod (e.g., PICkit3) with the free IDE environment called MPLAB from Microchip.  The 2x3 pinheader on the bottom side of the board closest to U1 pin 1 is used for connecting the programming pod to the NAT board.


Click photos to see larger image.
(Photo shows optional level translator for RS232 serial port.)



The NAT is shown in these photos, mounted in the recommended Hammond enclosure, with connectors along one side.  The "portrait" display orientation may be easily changed to "landscape" in software if, for example, a horizontal mounting of the NAT is desired in another enclosure.


Click photos to see larger image.


Parts List



Software ... Remember that the latest version software (ver 3) always includes all previous capabilities. You just need to load v3 to "have it all"!

Version 1:  Basic Functionality

Firmware V1 was the original firmware release providing basic functionality and operates either in Menu mode or in PLX mode. It only supports the keyboard for human input.

In Menu mode, PHSNA firmware generates menus that are displayed on the NAT display. Responses are input by the operator and sent to the PHSNA controller to specify operating parameters and to initiate various operations. Results are returned to the NAT for display and spooling to files on an SD card.

The PHSNA firmware can interface to an Excel spread sheet through a PLX-DEQ macro to access spread sheet cells via a port on the PC. The NAT emulates the spreadsheet-macro combination providing a more automated mode of operation. The PHSNA controller reads parameters from virtual spread sheet cells and returns results to other virtual spread sheet cells. The parameters defining the operation are contained in PLX forms that can be edited by the NAT operator.

NAT version 1.02 ... Hex file for loading with MPLAB.  Right-click and "save as" the default name (NAT_1_02.HEX) on your local drive. 
                               You may also use this file to update the NAT's firmware yourself.  See section 11 in the User Guide for use of hex files with the SDLD command.

PHSNA files optimized for use with NAT ...This zip file contains the latest version PHSNA that has been optimized for use with the NAT. (Shorter menus, etc.)
                                                                   Rick-click and "save as" the default name to your Arduino development folder or sketchbook.
                                                                   Unzip, then load your Arduino with the .ino file, per usual.

Version 2:  Touch Screen Input

Firmware V2 supports both the keyboard and the touch screen for human input. A numeric pad display was added to facilitate numeric input and some editing and navigating functions. The resulting functionality is about the same as V1 with the addition of some bug fixes and operating enhancements such as context menus, multi-color plots, spool file overwrite, and calibration interpolation and extrapolation. This version also added Signal Generator mode with which the user can manually specify and control the RF signal frequency.

NAT_V2.00 ... Right-click and save this file to your computer.  Then unzip the file to see the NAT_2_00.HEX file (place on your NAT's SD Card and issue the "SDLD" command to
                      update your NAT), and the modified PHSNA firmware V3.00 source (for programming the Arduino).  The corresponding versions of the user documentation are also included.

Release Notes v2.00


Version 3:  NACT Support

Firmware V3 incorporates the PHSNA controller functions. These functions are either controlled in PLX mode or in Command mode; Menu mode is not required. In addition to the obvious operating functions (frequency sweeps, power level capture, etc.) a number of new functions are implemented to help generate required operating parameters such and slope and intercept values and the DDS reference clock frequency. Since the serial interface is now available, DOS commands were added to upload and download files on the SD card to and from PC applications. Support was also added to allow a PC application to remotely control the SNA operations over the serial interface.

Version 3 hex file ... Right-click and save to your computer.  Unzip and then place the hex file onto a SD Card.  Insert SD Card to the NACT and use SDLD command to bootload new software onto the NAT.

Version 3 Release Notes


Version 4:  SNA Full Support

In theory, since the RF Power Meter has no control interface to the firmware, the firmware cannot tell the difference between a NACT and a SNA hardware configuration.  There are, however, some new setup functions that simplify the calibration process. A power meter mode was also added in V4 that measures and displays current, average and peak power levels.  The power meter range can be scaled using attenuators to cover picowatts to kilowatts.

[Version 4 coming this month!]




NAT Product Summary (HW-FW-Docs) ... This short document ties together the various firmware and hardware configurations and the project documentation.  The goal is to summarize the relationships between the firmware versions and hardware enhancements and to recommend a path to easier learning and familiarization of the NAT/NACT/SNA product capabilities and its evolution.  

SNA Power Point Presentation ... This slide presentation gives a general overview of the NAT to SNA development project and illustrates many of the device's capabilities. This is a good starting point for gaining familiarity with the NAT/NACT/SNA and its many capabilities.

Quick Reference Guide ... The Quick Reference Guide describes the various screen displays and how to use them. Some step-by-step instructions are included. The format is one topic per page with oversized print and lots of screen shots.

Quick Start Guide ... The Quick Start Guide describes many of the basic NAT operations along with some tips for interfacing to the PHSNA. Initial setup is covered including setting the serial port's baud rate, loading the PHSNA firmware, and formatting the SD card.  Basic operating modes are described along with examples. The appendix contains a listing of the hot keys available in various operating modes.

Tutorials ... A set of tutorials describes common, basic operations as step-by-step procedures. The tutorials also describe various accessory test fixtures and how to construct them as well as how to use them. The tutorial set will be updated as new features are added to the SNA.

0:   Reference Clock Calibration
This tutorial takes you through the steps to calibrate the reference clock which is a prerequisite to virtually all NACT operations.

1:  RF Power Meter Setup
This tutorial takes you through the steps to setup the RF Power Meter interface signal levels to interface with the NACT ADC.  This procedure should be performed before using the NACT to avoid exceeding the maximum voltage specification for the NACT’s dsPIC micro controller.

2:   RF Power Meter Slope and Intercept
This tutorial takes you through the steps necessary to determine and save the slope and zero intercept point for the RF Power Meter power curve.  This procedure should be done before using the NACT for DUT testing to assure the accuracy of the power level readings (dBm).

3:   Frequency Response Calibration
This tutorial takes you through the process of generating and capturing calibration data to account for variations in of the DDS output level at different frequencies.  The calibration data can be saved in EEPROM and reloaded every time the NAT is powered up.  This calibration sequence also normalizes the power readings such that they reflect the absolute power readings one would observe if the DDS were outputting a constant RF power level of one milliwatt.  Some basic Signal Generator mode operations are also described.

3T: Frequency Response Calibration
This tutorial takes you through the process of generating and capturing calibration data to account for variations in of the DDS output level at different frequencies using only the touch screen. The keyboard is not used.  The calibration data can be saved in EEPROM and reloaded every time the NAT is powered up.  This calibration sequence also normalizes the power readings such that they reflect the absolute power readings one would observe if the DDS were outputting a constant RF power level of one milliwatt.  Some basic Signal Generator mode operations are also described.

4:   Measuring DUT Frequency Response
This tutorial takes you through the steps necessary to perform frequency scans on a basic DUT (Device Under Test).  A “basic DUT” is one that does not require a test fixture and can be inserted directly into the test setup between the DDS output and the RF Power Meter input.  Basic DUTs include RF filters, RF cables, attenuators, etc.  The tutorial also covers the plotting, spooling, and playback of the scan results.

5:   Crystal Characterization and Matching
This tutorial takes you through the steps to test, grade, and sort a batch of crystals to select one or more groups of crystals for use in a crystal filter.  The sample filter used here is the 6-crystal filter used in the PHSNA Measurement Receiver designed by Jerry Haigwood, W5JH, and implemented and kitted by Jim Giammanco, N5IB ( ).  The principles demonstrated in this tutorial could be applied to most any other crystal filter design.  The object of this tutorial is to analyze a batch of 30 crystals to identify the six crystals with the minimum series resonant frequency variations or “spread”.  If we are lucky, we will be able to identify more than one group of crystals with acceptable frequency spreads.  The crystals used here were ordered as 3.2768 MHz and are all marked “3.27” (Mouser Part no. 520-HCA327-17X).

6:   Return Loss Bridge
This tutorial takes you through the steps to use a Return Loss Bridge (RLB) to measure the return loss and VSWR of a resonating DUT.

White Papers:  

SNA Calibration for Use in Your Shack ... Demystifying the approach and benefits of the NAT-SNA Calibration process.

User Guides:  

Ver 1 & Ver 2     ... The User Guide and its extensions are the most detailed reference source. The basic User Guide covers the Basic NAT and firmware versions 1 and 2.
Ver 3 Extension ...
The extension for V3 includes the NAT-to-NACT hardware upgrade instructions.
Ver 4 Extension ...
The extension for V4 includes the NACT-to-SNA hardware upgrade instructions.

SNA Option Pack Instructions ... Step-by-step pictorial description for making hardware changes to the NAT board, turning it into the NACT board (adding DDS connector, BNCs, input scaling resistors, 3dB pad resistors.)


Assembly Guide ... Step-by-step instructions for assembling and testing the NAT Kit.


Power-Up & Testing Guide ... Step-by-step instructions for ensuring that your newly-assembled NAT Kit is working right


Enclosure Specs ... Dimensional specifications for the recommended enclosure (Hammond 1591XX)


LCD Display Specs ... Information about the QVGA display



The NAT Kit has evolved into the SNA Kit, providing many new capabilities for approximately the same price.  Click HERE to order the SNA Kit.




Copyright 2014 Midnight Design Solutions, LLC.  All Rights Reserved.
Page last updated:  May 2014