Amqrp Aa-908 User manual

~ Assembly Manual ~

Micro908 Antenna Analyst

The Micro908 is a flexible and re-usable control platform for ham radio projects. The Micro908

platform is designed to be easily operated on the bench as well as in the field. It is comprised of a

single 5” x 5” printed circuit board containing all components, connectors, controls, LCD, and two

daughtercards. The plastic enclosure contains an 8-cell AA battery back enabling convenient field

use. A number of standard ham radio peripherals may be connected to the Micro908: antenna,

paddles, a PC-style keyboard, headphones, an audio line to drive an SSB transceiver, a keyline to

drive a transmitter, your rig's audio in/out signals, and custom control lines via an auxiliary jack. The

first major software available for the Micro908 platform is the Antenna Analyst – an instrument that

automatically determines SWR and complex impedance characteristics of an HF antenna system.

Advanced features of DDS frequency control, LCD tuning, PC data collection and plotting, numerous

operating modes and easy software upgradability make this instrument attractive for homebrewers and

antenna enthusiasts.

CONTENTS

Section 1: Introduction ......................................................................................................... 2

Section 2: Parts Inventory .................................................................................................... 3

Section 3: PCB Preparation ................................................................................................. 8

Section 4: Installing the Surface Mount Components ........................................................ 10

Section 5: Installing the Controls and Connectors.............................................................. 15

Section 6: Power-up and Test ............................................................................................ 20

Section 7: Installing the PC Board in the Enclosure........................................................... 21

Section 8: Troubleshooting ................................................................................................ 23

Appendix A: Parts List ........................................................................................................... 26

Appendix B: Schematic .......................................................................................................... 29

Appendix C: Component Layout ........................................................................................... 31

Appendix D: Fully-Assembled PC Board .............................................................................. 33

Appendix E: Mechanical Assembly Diagram ........................................................................ 34

Appendix F: Quick Reference Sheet ..................................................................................... 35

Appendix G: Loading New Software into the Micro908 ....................................................... 36

Appendix H: Making a Dummy Antenna for Testing ............................................................ 37

Section 1: Introduction

Welcome to the Micro908 Antenna Analyst Kit, a reprogrammable and multi-use microcontrolled instrument that will

provide years of reliable service in both the shack and the field when constructed according to this assembly guide.

This project involves the soldering of small surface mount technology (SMT) parts and other delicate components to a

printed circuit card, and it will take about six hours to assemble – perhaps several evenings or over a weekend. Once the kit

is assembled, the pre-programmed controller (the HC908 Daughtercard) may be inserted into place and immediate

indication of product operation will be seen.

This Assembly Manual provides detailed, step-by-step instructions on preparation of the components, installation of them

to the printed circuit board and enclosure, and basic calibration and operation of the instrument. Other documents provided

on the enclosed CDROM describe the technical overview and more detailed usage. Several useful software programs are

also contained on this Micro908 Resource CDROM, such as a software loader application and a terminal program.

Additionally, the CD contains information and full software source code that will be useful for those wishing to develop

custom software for the Micro908 platform.

Please regularly visit the Micro908 project website (www.amqrp.org/kits/micro908) to download updated versions of the

software, manuals and schematics. We are also maintaining a list of frequently asked questions (and answers) that will

surely be of help to you in building and using this kit. An even more complete and up to date Assembly Manual, with

additional photos (all in color) may be found at the Micro908 online site.

We’ve made every effort possible within reason to make construction and use of the Micro908 Antenna Analyst a success

for the builder. Please let us know how it works out for you or if you have any questions along the way. We thank you for

purchasing the Micro908 Kit from the AmQRP Club and we wish you good luck in building and using it!

Sincerely yours,

“The Micro908 Team”

George Heron, N2APB n2apb@amqrp.org

Joe Ev erhart, N2CX n2cx@amqrp.org

Tom (W8KOX) & Nancy (NJ8B) Feeny, w8kox@amqrp.org

David Willmore, N0YMV, willmore@optonline.net

Section 2: Parts Inventory

Carefully review the contents of each parts bag and component supplied in the kit to ensure that you have everything

needed at the start of the project. If a part is missing, please contact us by email and we’ll get it out to you right away.

Surface Mount Components Sheet

Controls & Connectors Bag

1 J1 BNC, pcb mount

1 J2 Serial port connector, DB9F

1 ENC Rotary Encoder

1 J4 Coaxial pow er connector, 2.1mm

1 J8 Socket, 1x12 pos'n (DSP out)

1 J9 Socket, 2x10 position, (DSP in)

1 J11 Mini-DIN, 6 pos'n (KBD)

3 J6, J7, J12 Audio jack, 1/8", pcb mount

1 J10 Socket, 1x8 pos'n, right angle

1 J14 Mini-Din, 8 pos'n (AUX)

1 W1 Jumper, Flexstrip, (LCD)

2 P1, P2 Pinheader, 2x34 (HC908) (cut 2 f rom 2x72 strip)

2 P3, P4 Pinheader, 1x2 pos'n (MON) (cut from 2x72 strip)

3 C7, C33, C34 Capacitor, 1 uF, Electrolytic, SMT

2 C5, C26 Capacitor, 10 uF, Electrolytic

1 C27 Capacitor, 47 uF, Electrolytic

1 C24 Capacitor, 100 uF, Electrolytic

1 R45 Potentiometer, 10K, miniature, pcb mount

1 S2 Slide sw itch, pcb mount, SPST

5 PB1, PB2, PB3, PB4, PB5 Pushbuttons, SPST, momentary contact

1 SPKR Speaker, miniature, 32-ohm

5 Pushbutton caps (black)

1 Heatsink - TO220

1 Knob, 1/4"-dia shaft, (ENC)

1 Nut, zinc plated, 4-40 (U1)

1 Machine screw , zinc plated, round head, 4-40 x 0.5" (U1)

4 Spacer, nylon, hex tapped, 4-40x0.25" (LCD)

6 Spacer, nylon, hex tapped, 4-40x0.375" (PCB+DDS)

16 Machine screw , pan slotted, #4-40x0.25" (PCB+DDS+LCD)

4 Machine screw , flat slotted, #4-40x0.25" (PCB-cover)

1 Desoldering Braid

1 Solder, 63/37 Eutectic, No-Clean Flux, @28 ga.

Overlay Bag (Included with Enclosure Option)

1 Front panel overlay

1 Side panel overlay

1 End panel overlay

1 End panel (drilled)

1 End panel (undrilled)

4 Enclosure screw s

4Enclosure rubber f eet

Battery Holder Bag

1 LCD Display, LCD, Hantronix, 16x2 STN, GRAY

1 J3 Battery holder, 8-AA cells

1 Flux Pen, No-Clean

Semiconductor Bag

1 U1 Voltage regulator, 3-terminal, 7805

1 U2 Me mor y , SEEPROM, 512Mb

2 U3, U4 IC, Op Amp, LMC6484, SOIC

1 U5 IC, Audio Amp, LM386, SOIC

1 U6 IC, Level Translator, TC7SET08F, SOIC

1 LED1 LED, T1- 3 / 4 ( BUSY )

2 Shunt shunt, 0.1", 2 pos'n

3 D7, D8, D9 Diode, Schottky, 1N5817, DO-41

1 VR1 - DDS Option Voltage Regulator, 78L08, 8V (optional, f or use w ith regarg

1 Q1 Transistor, NPN, 2N3904, TO92

PCB Bag

1PCB PC Board

HC908 Daughtercard Bag (Optional)

1HC908 HC908 Daughtercard assembly

DSPx Daughtercard Bag (Optional)

1DSPx DSPx for Micro908 assembly

DDS Daughtercard Kit Bag (Optional)

1DDS Ki

DDS Daughtercard Kit

Keyboard Cable Bag (Optional)

1 Cable Keyborad extension cable (6')

Keyboard (Optional)

1Keyboard Dauphin Mini Keyboard

Enclosure (Optional)

1Enclosure Pac-Tec LH-57 Enclosure (pre-drilled)

Section 3: PC Board Preparation

Meet the Micro908 PC Board! You should become familiar with the orientation nomenclature that we’ll be using

throughout this manual.

Top, “Component” Side

Left Right 

Bottom, “Ground”, “Controls” Side

Left Right 

Section 4: Installing the Surface Mount Components

Preparing for the job

The key to being successful with any construction project is selecting and using the proper tools. For projects using SMT

(Surface Mount Technology), the tools are easy to find.A magnifying lamp is essential for well-lighted, close-up work on

the components. Tweezers or fine-tipped pliers allow you to grab the small chip components with dexterity. Thinner

solder (.015”) than you might normally use is preferred because of its being quicker to melt and smaller in solder volume

on the component lead. Use of a super fine-tipped soldering iron make soldering the leads of these small parts

straightforward and easy. A clean work surface is of paramount importance because SMT components often have a

tendency to fly away even when held with the utmost care in tweezers – you’ll have the best chance of recovering your

wayward part if your table is clear. When the inevitable happens, despite your best efforts of holding an SMT part in your

tweezers, you’ll have lots of trouble finding it if it falls onto a rug-covered floor covered. It’s best to have your work area

in a non-carpeted room, for this reason as well as to protect static-sensitive parts.

Attaching SMT Components to the PC Board

We’ve supplied two items in this Micro908 Kit that will greatly help you successfully solder these small surface mount

components to the pc board. The first is a small coil of .015” solder. As described above, this thin solder is perfect for

soldering small SMT parts. Just wrap the solder around a convenient tube as shown below on the left) so you can easily

play out the solder as you go along in the board assembly. The other helpful item is the Flux Pen. By making the pads to

be soldered wet with the liquid flux, you are greatly helping the joint be clean and ready to accept the soldered component.

(Just press down a little on the tip of the flux pen and the liquid flux will start flowing out through the sponge tip.) In order

to solder these small components in place, having a fine-tipped, 600-700 degree soldering iron is essential, as illustrated in

the rightmost photo below.

Thin solder (.015”) is coiled around a glue stick. Flux pen applies flux to pads. Fine tipped iron solders in SMT resistor.

The trick to soldering surface mount devices to pc boards is to (a) pre-solder one of the pads on the board where the

component will ultimately go; (b) hold the component in place with needle nose pliers or tweezers on the tinned pad; (c) re-

heat the tinned pad and component to reflow the solder onto the component lead, thus holding the component in place; and

lastly (d) solder the other end of the component to its pad.

Attaching a Surface Mount IC

There are four surface mount integrated circuits to attach on the Micro908 pc board: U2 (memory chip), U3 & U4 (op

amps), U5 (audio amp) and U6 (a pretty tiny driver IC). Pre-solder the pad in one corner of the given layout then carefully

position the leads of the IC over its set of pads on the pc board. I generally use my fingers to carefully align the IC over all

its pads and then reheat the corner pad to reflow the solder onto the IC pin. This should leave the IC attached by that pin.

Again making sure the IC pins are aligned over all pads, carefully solder the opposite corner lead to its pad. This should

leave all other pins of the IC aligned over their respective pads, making it easier to solder them. Next solder each of the

other pins to their respective pads, being careful not to bridge solder across any adjacent pads or pins. If this does happen,

that’s okay! Just grab some solder wick (also supplied in the Micro908 Kit) and use it to draw off the excess solder, which

should be fairly easy and clean because of the solder mask on the circuit board.

First corner pin of surface mount IC being attached. Solder wick easily absorbs excess solder between pins.

(IC shown being attached here is the DDS chip onto the DDS Daughtercard. The techniques are the same for the Micro908 ICs.)

Using the Component Layouts During Assembly

A helpful practice to develop is to mark the supplied Layout diagram as you install each component. As you go along, the

diagram will fill up with more and more marks, enabling you to more easily find the location of the remaining components,

and have confidence that you haven’t omitted installation of a component along the way.

A useful marking technique is to identify with a “dot” the location of the parts you are about to install, making it easier for

you to place and solder the part in the right spot. Once soldered in place, going back to the diagram and placing a full line

in that same spot will indicate that you’ve soldered it in place, as shown in the photo on the right.

The component layout diagram is a useful tool if you mark it up as you proceed along in installing the components.

1) Install components from Resistor Card 1 section of the SMT Sheet

Using the Component Layout Diagram in Appendix A as a guide, install the SMT components from the Resistor Card 1.

Check off each row as you complete installing those components.

QTY

[ ] 1 R46 Resistor, 10, SMT, 1206

[ ] 3 R11, R12, R14 Resistor, 49.9, SMT, 1206, 1%

[ ] 1 R7 Resistor, 330, SMT, 1206

[ ] 1 R8 Resistor, 1K, SMT, 1206

[ ] 1 R6 Resistor, 4.3K, SMT, 1206

[ ] 1 R44 Resistor, 4.7K, SMT, 1206

[ ] 4 R37, R38, R39, R40 Resistor, 5.1K, SMT, 1206

[ ] 12 R1, R2, R3, R4, R5, R17, Resistor, 10K, SMT, 1206

R18, R22, R23, R27, R42, R48

2) Install components from Resistor Card 2

Using the Component Layout Diagram in Appendix A as a guide, install the SMT components from the Resistor Card 2.

Check off each row as you complete installing those components.

QTY

[ ] 1 R41 Resistor, 10.0K, SMT, 1206, 1%

[ ] 1 R28 Resistor, 22K, SMT, 1206, 1%

[ ] 4 R10, R13, R15, R49 Resistor, 47K, SMT, 1206

[ ] 4 R19, R24, R29, R51 Resistor, 71.5K, SMT, 1206, 1%

[ ] 4 R16, R21, R26, R50 Resistor, 220K, SMT, 1206, 1%

[ ] 3 R20, R30, 52 Resistor, 221K, SMT, 1206, 1%

[ ] 1 R25 Resistor, 549K, SMT, 1206, 1%

[ ] 4 R32, R33, R34, R54 Resistor, 1M, SMT, 1206

3) Install components from Capacitor & Diode Card

Using the Component Layout Diagram in Appendix A as a guide, install the SMT components from the Capacitor & Diode

card. Check off each row as you complete installing those components. Be careful to identify the cathode of the diodes on

this card. The cathode is the side of the diode with a single straight line on the schematic symbol, and with a (faint) single

straight line on the package. You will surely need to use your magnifying glass to see this mark. Orient the end of the

diode with the single straight line onto the pc board with the diode outline also containing the straight line indicating the

cathode.

[ ] 4 C17, C19, C21, C41 Capacitor, 220 pF, SMT, 1206

[ ] 2 C31, C32 Capacitor, 560 pF, SMT, 1206

[ ] 7 C18, C20, C22, C23, Capacitor, 0.01 uF, SMT, 1206

C28, C40, C42

[ ] 16 C1, C2, C3, C4, C6, C11, Capacitor, 0.1 uF, SMT, 1206

C12, C13, C14, C15, C25,

C35, C36, C37, C38, C39

[ ] 2 C29, C30 Capacitor, 0.33 uF, SMT, 1206

[ ] 10 D1, D2, D3, D4, D5, D6, Diode, Schottky, 1N5711, SMT (These diodes have faint cathode markings)

D10, D11, D12, D13

For now, don’t install this leftover part on the SMT sheet. But don’t lose it! (We just wanted to mention this up front!)

[ ] 1 U6 Integrated Circuit, Level Translator, TC7SET08F

5) Install components from Semiconductor Bag

Using the Component Layout Diagram in Appendix A as a guide, install the components from the Semiconductor Bag.

Check off each row as you complete installing those components.

QTY

[ ] 1 U1 Voltage regulator, 3-terminal, 7805

[ ] 1 Heatsink - TO220 (From Controls Bag)

Position the voltage regulator over the mounting hole to determine where to bend the three leads so they can be inserted to

the pc board as shown below. Before soldering in place, orient the heatsink as shown and use the metal screw & nut to

connect the two components to the pc board. Then, when aligned nice and straight, solder the three leads of U1 to the

pads.

[ ] 1 U2 Memory, SEEPROM, 512Kb (16-pin surface mount IC.)

[ ] 2 U3, U4 IC, Op Amp, LMC6484, SOIC (14-pin surface mount IC packages.)

[ ] 1 U5 IC, Audio Amp, LM386, SOIC (8-pin surface mount IC.)

[ ] 1 U6 IC, Level Translator, TC7SET08F, SOIC (Very small 5-lead surface mount IC.)

(This is the leftover component from the SMT sheet.)

[ ] 3 D7, D8, D9 Diode, Schottky, 1N5817

[ ] 1 Q1 Transistor, NPN, 2N3904, TO92 (Familiar 3-lead thru-hole package.)

U4 op amp U6 translator U2 SEEPROM Memory U5 LM386 Audio Amp

Section 5: Installing Parts from the Controls and Connectors Bag

1) Install Pinheaders & Sockets

Using the Component Layout Diagram in Appendix A as a guide, install all pinheaders and strip sockets on the Component

side of the board …

QTY

[ ] 2 P1, P2 Pinheader, 2x34 (HC908)

It’s really important to insert the longer-side pins of P1 & P2 into their respective holes from the Bottom/Controls side of

the pc board. Then, since the black plastic part of the connector body is on the bottom, you’ll need to carefully solder the

pins on the Top/Component side. When you solder the pins, take care to not let the solder wick up the pins, as the HC908

Daughtercard sockets will need to fit down onto these pinheaders. (Just heat the pad and very lowest part of each pin, then

quickly apply a *small* amount of solder.) When all the pins have been solders, snip off the pins on the Bottom/Controls

side of the pc board. See photos below for reference.

[ ] 2 P3, P4 Pinheader, 1x2 pos'n (MON & NiMH)

[ ] 1 J8 Socket, 1x12 pos'n (DSP out)

[ ] 1 J9 Socket, 2x10 position, (DSP in)

[ ] 1 J10 Socket, 1x8 pos'n, right angle (for DDS Daughtercard)

This is the right-angle connector for the DDS Daughtercard and it will be important to get it soldered in at the correct

height above the pc board. First install one nylon spacer to the Top/Component side of the pc board located at the top

right corner of the silkscreen indication for the DDS card. (This hole is located near components R15.) Use nylon screw

to hold it in place. This single standoff will be the resting point for the DDS card once it is installed. Next, stick J10 on

the end connector of your DDS Daughtercard with the pins of J10 extending down toward the bottom/ground side of the

DDS card. Insert the pins of J10 into the pc board from the Top/Component side such that the attached DDS card is resting

on the just-installed nylon spacers. Solder the J10 pins from the bottom side while holding the DDS card steady and

parallel to the pc board, and snip off the pins. Proper orientation will be as shown below

2) Install Thru-hole Components

Using the Component Layout Diagram in Appendix A as a guide, install all thru-hole components on the Component side

of the board …

QTY

[ ] 3 C&, C33, C34 Capacitor, 1 uF, Electrolytic

Note that an engineering mod has already been done to the board in the positions for C33 and C34 to correct for a pad

layout error. In each case, the longer/positive lead of the capacitor goes in the ‘+’ pad, and the negative lead goes in the

small ‘via” hole associated with the test point for that signal line (neg lead of C34 goes to the ‘Aud-L’ hole, and the neg

lead for C33 goes to the ‘Aud-R’ hole.) You will need to scrape the green soldermask off these small holes using a sharp

razor blade, thus exposing the copper for soldering.

[ ] 2 C5, C26 Capacitor, 10 uF, Electrolytic

When installing these radial-lead, thru-hole electrolytics, be sure to properly identify the component polarity. As

shown in the photo below, the longer lead is the positive and the shorter is the negative (which is also identified with the

black stripe on the side of the component.) Be sure to insert the positive/longer lead in the pc board hole closest to the

silkscreened ‘+’ sign.

[ ] 1 C27 Capacitor, 47 uF, Electrolytic

[ ] 1 C24 Capacitor, 100 uF, Electrolytic

[ ] 1 R43 Resistor, 10, 1/2W

[ ] 1 R47 Resistor, 47, 1/2W

3) Install Connectors

Using the Component Layout Diagram in Appendix A as a guide, install most connectors on the Component side of the

board. It is very important to mount these components on the Top/Component side of the pc board. Most of these

connectors and their pads are symmetrical, so you could mistakenly mount them on the wrong side. Double-check the

Completed PC Board Assembly photos in Appendix E to ensure that you are inserting these connectors to the proper side of

the pc board.

QTY

[ ] 1 J1 BNC, pcb mount

[ ] 1 J2 Serial port connector, DB9F

[ ] 1 J4 Coaxial power connector, 2.1mm

[ ] 1 J11 Mini-DIN, 6 pos'n (KBD)

[ ] 3 J6, J7, J12 Audio jack, 1/8", pcb mount (remove mounting nut)

[ ] 1 J14 Mini-Din, 8 pos'n (AUX)

[ ] 1 S2 Slide switch, pcb mount, SPST

4) Install Controls

Using the Component Layout Diagram in Appendix A as a guide, install all controls on the Bottom/Controls/Ground side

of the pc board. It is really important to install these components on the Bottom/Controls side of the pc board. Double-

check the Completed PC Board Assembly photos in Appendix E to ensure that you are inserting these connectors to the

proper side of the pc board.

QTY

[ ] 1 ENC Rotary Encoder

The encoder needs a little preparation before you assemble it to the pc board. Using some side cutters/diagonals (and

preferably heavy-duty ones), you must first snip off the zinc cast alignment nub that sticks up in the same direction as the

shaft. Taking off this small piece will allow the encoder to sit flush up underneath the front panel of the enclosure. Also,

the encoder shaft is too long for our purposes here, so you’ll need to use a hack saw (or equiv) to saw off about one half

the length of the flat-sided end of the shaft. This will leave about ¼” of the flat shaft, which will be fine for attaching the

knob later on.

[ ] 1 R45 Potentiometer, 10K, miniature, pcb mount

[ ] 5 PB1, PB2, PB3, PB4, PB5 Pushbuttons, SPST, momentary contact

When installing these pushbuttons, it’s very important to orient them as shown in the photo below. Each pushbutton must

have the while tabs on the side of its body oriented to the right/left of the board (i.e., toward the speaker and J9).

Otherwise the switch input lines to the MPU will always be shorted.

[ ] 5 Pushbutton caps

[ ] 1 SPKR Speaker, miniature, 32-ohm

When soldering this component in place, be careful to orient the leads so the pin marked with a ‘+’ is placed in the hole

clsest to the silkscreened ‘+’. Be sure not to apply too much heat while soldering, as the plasic of fthe speaker body can

easily melt and deform. Lastly, leave the speaker a little elevated (about .04”) from the pc board, as this will allow it to

better reach up to the front panel hole. See photo below for reference.

[ ] 1 LED1 LED, T1-3/4 (BUSY) (From Semiconductor Bag)

The the cathode of the LED is indicated by the shorted lead and a slight notch in the side of the red plastic body. The

catchode must be mounted toward the upper end of the board, toward the straight line indication on the silkscreen. In

order for the LED to reach up through the front panel, it should be mounted about 0.3” up off the pc board. See the photo

below for reference.

4) Install Test Points

We provided for some important signals to be readily accessible to your DVM or oscilloscope probes during the instruction

checkout. These “Test Points” are merely small “loops” of wire made from of scrap component leads that are soldered onto

adjacent pads on a trace of a specific signal.

(Note: installation of the wires in this small test point holes is optional. If you do install them, you will need to gently

scrape away the green soldermask from the holes to expose the copper pads, thus enabling the test point wires to be

soldered.)

[ ] Install Test point ‘GND’ located in lower left corner of the board.

[ ] Install test point ‘+V’ located in lower-middle area of the board.

[ ] Install test point ‘RF’ located in the top-right corner of the board.

[ ] Install test point ‘+5’ located to the right of regulator U1.

[ ] Install test point ‘Aud-R’ located in the middle of the board near C33.

[ ] Install test point ‘Aud-L’ located in the middle of the board near C34.

Another project board is shown here to illustrate installation of a test point.

5) Install LCD

Using the Component Layout Diagram in Appendix A as a guide, install the LCD on the Bottom/Controls/Ground side of

the pc board …

QTY

[ ] 1 LCD Display, LCD, Hantronix, 16x2 STN, GRAY

[ ] 1 W1 Jumper, Flexstrip, (LCD)

You’ll use the 16-wire flexible jumper W1 to connect the LCD to the pcb, as shown in the photos below. Bend the wire

jumper at the midpoint and fold it out (away) from the LCD as shown below in preparation for attaching the LCD to the

nylon standoffs on the pc board. (Folding outward keeps the pins from the LCD pcb from rubbing/penetrating the

insulation and shorting to the signals.)

Locate eight nylon screws and using your wire cutters/diagonals, nip 1/16” off the end of each. This amounts to about

1.5-2 “threads” as you position the cutters on the shaft of the screw, as shown below. We have to do this because the

spacers we’ll use in the next step are short and the screws will not insert far enough to seat the LCD on one side and the pc

board on the other.

Locate the four shorter, 0.25” nylon spacers. Be sure these are the shorter ones supplied in the kit. Attach all four spacers

on the Bottom/Controls side of the pc board using four of the shortened nylon screws, as shown in the upper-right photos.

Be careful not to over-tighten the nylon hardware, as you’ll strip out the threads.

Next, you will screw the four remaining shortened nylon screws through the corner holes of the LCD and into the threaded

spacers mounted on the board. NOTE: The four holes in the corners of the LCD are smaller than the screws, but by

applying a little pressure while turning them into the holes, you will “thread” them into the holes and subsequently into the

spacer below. (If you have trouble with this, you can use an appropriately-sized drill bit to carefully enlarge the LCD

mounting holes.) Again, be careful not to over-tighten the nylon hardware. When complete, the LCD should look as

shown in the upper-right photo.

Section 6: Power-up and Test

[ ] Prepare for the Tests

When first ready to apply power to the newly-assembled Micro908, position the pc board on the bench (without the

enclosure) and with the LCD and controls side facing up. This will enable you to more easily get to the components and

you can spot gross problems (like exploding capacitors, smoking regulators, etc.) should they occur.

Make sure the shunt (small, black 1x2 position jumper socket) is removed from P3.

Install the HC908 Daughtercard. Make certain the Heartbeat LED is oriented toward the bottom of the Micro908 pc board,

as shown in Appendix D: Fully-Assembled PC Board

Do not install the DDS Daughtercard yet.

Do not install the DSP Daughtercard yet.

It’s a good practice to use a current-limited external power supply when first testing out projects like the Micro908. You

can set the maximum current to be about 500ma and be assured that a short circuit will not blast away circuit traces in the

process of first applying power. A good alternative is to power the project from a battery on the bench. The similar effect

can be gained by the natural limits of a battery to supply lots of current.

[ ] Apply power and see display on LCD

After plugging in the power supply and moving the Power slide switch to the ON position (up), you will see the

approximate power supply voltage displayed in the LCD for about ½ second, then the LCD will display the “main menu”

message of “AA908 v2.0” on the first line, and “Select Command” on the second line.. If you don’t see this indication on

the LCD, proceed to the Troubleshooting section.

[ ] Press MODE Pushbutton and see Frequency, SWR, R and X display on LCD

Pressing MODE pushbutton (also called the Manual Mode) will the displayed values for frequency, SWR, R and X

displayed on the LCD. (You might need to turn the Dial a bit to see the full display appear.) The readings for SWR, R and

X will be meaningless at this point since you do not yet have the DDS Daughtercard (i.e., the RF signal source) installed.

[ ] Turn Dial to Change Frequency

Turning the Dial will result in changing the displayed frequency, starting at the digit that has the underline cursor beneath

it. This digit will be the 10 kHz digit.

[ ] Press and Turn Dial to Change Cursor Position

When you press-and-turn the Dial, the underscore cursor will move to the next-higher (or next-lower) digit in the frequency

display, thus allowing you to change frequency at a more (or less) rapid rate. The cursor will stop at the rightmost digit

despite further clockwise rotation of the Dial, thereby providing 10 Hz increments as the smallest allowable. Similarly, the

cursor will stop at the leftmost position despite further counterclockwise rotation of the Dial, thereby providing 10 MHz as

the greatest incrementing value of frequency.

[ ] Press the BAND Pushbutton to Select Band

You can press the BAND pushbutton at any time to select one of four bands segments to automatically scan when you later

press the SCAN pushbutton. The band segments are 1-10 MHz, 10-20 MHz, 20-30 MHz and “Custom Band”. (The

Custom Band uses start/end limits that were previously set in the Configuration menus, discussed later.) The different

Band segments are sequentially displayed while turning the Dial. A band is selected by pressing the Dial when the desired

band is displayed. Once a band is selected, the display will show the Main display (“AA908 v2.0” / “Select Function”.)

[ ] Press the SCAN Pushbutton to Scan the Band

When you press the SCAN pushbutton, you initiate an automatic scan of the selected band. The LED is illuminated and the

internal DDS signal generator is automatically set to the Start frequency for that band and the SWR is determined. The

frequency is incremented by the Step value (default of 10 kHz and user-settable in Config) and the SWR is determined at

this point. This sequence continues throughout the entire band until the End frequency is reached. Throughout the

scanning, the software saves the frequency that yielded the lowest SWR and when the scan is complete, control is given to

the Mode function that displays that point of lowest SWR. The display will show the frequency, SWR, R and X values for

that point and the user is able to manually control the instrument as described in the Mode section above. Since the DDS

signal generator is not yet installed, the Scan will likely exit showing a frequency of 1,000.00 MHz and an SWR of ‘>10’.

This is okay for now. If the LED did not illuminate at the start of the Scan, and turn off at the end of the Scan, make a note

to visit the Troubleshooting section later on.

[ ] Press the CONFIG Pushbutton to get into the Configuration Menus

The CONFIG pushbutton may be pressed at any time to access the Configuration menus. Please refer to the Micro908

Technical Reference and Operation Guide for a complete description of the available functions in this mode. But in

summary, the user is allowed to specify Start/End frequencies and Step size for a Custom Band, turn the Tones On/Off,

Update the Software, turn on DEBUG Mode, access the low-level Debug Monitor (HCmon), Display the battery voltage,

Calibrate the instrument, and Exit back to the Main display.

[ ] Select TONE ON to hear Audio Indication of SWR

While in the Configuration menus, turn the Dial until ‘Tone ON’ is displayed and then press the Dial to select it. Rotate the

Dial until ‘Exit’ is displayed and press the Dial to exit. A message on the second line of the LCD will indicate that the

changed settings are being saved (to nonvolatile EEPROM memory) and then the Main display will show once again. Press

the MODE pushbutton to see the frequency display in Manual Mode and immediately hear a high-pitched tone coming

from the speaker, indicating that a high SWR reading is currently being displayed. If you do not hear a tone, make a not of

later checking it out in the Troubleshooting section. When we later install the DDS Daughtercard and an antenna (or

dummy antenna), you will note a variable pitch being generated when the Dial is tuned through a resonance. A lower tone

indicates a lower SWR being measured. In order to preserve your sanity (and hearing) during the remainder of the tests, go

back into Configuration menu to turn the Tone OFF.

[ ] Select ‘Software Load from CONFIG Menu

You will test the RS232 serial port on the Micro908 now, so connect a 9-pin, “straight-through” serial cable (not a “null

modem cable”) between your Micro908 pc board (connector J2) and a PC running a dumb terminal program such as

HyperTerm. Configure the terminal program to run with settings of “9600 N81” (9600 baud, No parity, 8 bits, 1 stop bit).

In the Micro908 Configuration menu, select ‘Software Load” and see a line of data displayed on the PC screen that shows

“HCmon>” and intelligible letters and numbers following it. If you do not see this indication on the PC screen, make a note

to check it out in the Troubleshooting section.

[ ] Turn the Micro908 power switch S1 to OFF

[ ] Install the upgraded DDS Daughtercard

After making the improvements to the DDS Daughtercard (per the simple instructions provided in that kit bag), install the

DDS card into its connector J10. There will be no need to attempt to screw the DDS card onto the nylon standoff, as the

holes do not line up. The DDS card should just sit atop the standoff with a little pressure.

[ ] Turn on the power to the Micro908

After siding S1 back to ON, check that there is no smoke, sizzle or unexplained flashes of light coming from your DDS

Daughtercard. The DDS chip, the MAV amplifier and the R4 bias resistor will indeed get warm to the touch, but not

excessively so. If they do, power down immediately and go to the Troubleshooting section.

[ ] Attach Dummy Antenna to BNC connector J1

We’re going to measure some antenna characteristics here so you’ll need a load. Ideally at this point, you should connect a

“dummy antenna” that you might have previously prepared, per Appendix F. Alternatively, you can connect an antenna that

is known-resonant at some frequency within the HF bands.

[ ] Get into Manual Mode (MODE Pushbutton) and See Measurements Change

When you get into the Manual mode (by pressing MODE pushbutton), move the frequency up/down until you see a dip

occur in the SWR display, indicating that you are approaching the resonant point of the dummy antenna. When you have

found the minimum SWR “dip”, move the cursor to the next lower position (by press-and-turning the Dial to move the

underscore cursor) and continue turning the Dial to get finer resolution of the minimum SWR point. If you do not see this

SWR dip condition happening, go to the Troubleshooting section to dig into the problem.

[ ] Select the Band that has the Resonance and SCAN

Make sure you have selected the Band that contains the known-resonant frequency (1-10, 10-20 or 20-30 MHz) and press

SCAN. The instrument will scan the band, and at the end it will display the antenna characteristics (SWR, R and X) found

at the point of minimum detected SWR.

[ ] Calibrate the Micro908 reflectometer channels for gain

You will need to calibrate the Micro908 Antenna Analyst when first constructed. The instrument may also need to be

recalibrated later, such as when a new software update is available that changes the way in which calibration data are used,

or when the level of the DDS signal source changes in any regard. In these cases, the instrument may be quickly and easily

calibrated by following a short sequence of operations located in the “Calibrate” function, located beneath the CONFIG

pushbutton.

1. Select the Calibrate function, located within CONFIG.

2. See “Calibrate now?” displayed in the LCD. Confirm by selecting “yes” with the dial. (Press the dial when “yes”

is displayed.)

3. See “Open load?” displayed on the LCD. Ensure that nothing is connected to the RF output jack, then confirm by

selecting ”yes” with the dial.

4. See a display of four 2-digit hexidecimal numbers representing the reflectometer channel voltages for Vf, Vr, Vz

and Va. If a trimpot is provided on your DDS Daughtercard, adjust it such that none of the readings exceeds about

C2. This will correspond to a voltage on the open circuit BNC output connector approximately equal to 2 volts

peak-to-peak (as seen with an oscilloscope) or about 700 mVrms (as seen with an RF probe on a DMM). Ensure

that the first three hex numbers are these “high” values and that the last number (Va) is very close to zero (e.g.,

04). [NOTE: See the “Hexidecimal numbers” explanation at the bottom of the page.]

5. If the displayed numbers are in the acceptible range, as explained above, press the Dial with “yes” selected in

order to continue. However, if the “3 high and one low” condition of numbers is not present, or if any channel is

very high in the hex number range of F0 to FF, then a successful calibration is not possible and you should contact

Support.

6. See “Shorted load?” displayed on the LCD. Place a short circuit on the RF output jack and select “yes” with the

dial. [NOTE: You might consider constructing a shorted BNC plug to to conveniently serve as this shorted load.]

7. See “270-ohm load on?” displayed on the LCD. Pleace the supplied 274-ohm resistor on the RF output connector

and confirm by selecting “yes”. [NOTE: You might consider constructing a BNC plug containing this 274-ohm

resistor to conveniently serve as this load.]

8. See “Make SWR=5.4” displayed on the first line of the LCD, and a number on the second line. Adjust the dial to

make the number on the second line be as close as possible to 5.4. Press the dial when this number is 5.4.

9. See “50-ohm load on? displayed on the LCD. Pleace a the supplied 49.9-ohm resistor on the RF output connector

and confirm by selecting “yes” with the dial. [NOTE: You might consider constructing a BNC plug containing

this 49.9-ohm resistor to conveniently serve as this load.]

10. See “Saving data” displayed on the LCD and the red BUSY LED will turn on for several seconds.

11. When the BUSY LED turns off, “Exit” will be displayed on the LCD. Confirm by pressing the dial and control

will again be placed in the Impedance mode, with measurements being made using the newly-created calibration

data.

Aside 1: “What is being calibrated?”

In order to normalize the gains of the four reflectometer channels with respect to each other, the software creates “gain

correction factors” for the Vr, Vz and Va channels. When each channel is multiplied by its respective correction factor, it

will equal the value of the Vf channel, as determined under the specific conditions of open/short/50-ohm loads presented

during the calibration sequence. These correction factors are then used during the normal operation of reading raw Vr, Vz

and Va signals to compute the SWR, R and X values displayed on the LCD in Impedance mode. The correction factors are

saved away to nonvolatile memory such that they can be used each time the instrument is turned on.

Aside 2: The Importance of a Good DDS Signal

We have a spectrum analysis screen shot representative of a well-calibrated Antenna Analyst on the Micro908 project page

at http://www.amqrp.org/kits/micro908. It shows the second harmonic >30 dB down from the fundamental, which is a very

good and important characteristic of the DDS signal generated in the instrument.

Signal quality such as this is important for use with the Antenna Analyst where an RF signal is being used as a test

stimulus, and is correspondingly being measured with an antenna network attached. The signal should be as purely

sinusoidal as possible such that that the signal integrations being made in the reflectometer, and being amplified by U3 and

U4, and being measured by the microcontroller, are accurate representations of the characteristics of the antenna system at

the frequency of interest.

In contrast, if the harmonics of the DDS signal (i.e., frequency components other than just the fundamental frequency

displayed on the LCD) are too high in level compared to the fundamental, the accuracy of the Antenna Analyst suffers. The

harmonics are also being integrated by the reflectometer, right along with the “good” fundamental frequency, and they start

affecting the measured results. We don't want frequencies other than the fundamental to be used - otherwise, the

computed/displayed results will be inaccurate for the frequency we desire.

So, the moral of the story is to adjust the DDS card to generate the best-looking signal possible! If you have an

oscilloscope, check the open circuit voltage at the output BNC connector to ensure that its sinusoidal symmetry is good and

that its level is approximately 2V p-p. If you also have a spectrum analyzer, you should ensure that the signals harmonics

are all more than 30 dB below the level of the fundamental frequency.

Aside 3: “What is a hexidecimal number?”

You might not understand the meaning of a voltage of 'C2’ as displayed on the Micro908 LCD during calibration, so here is

a brief "hexidecimal numbering" primer that will explain how hexidecimal notation is used in the Micro908 and most other

computers.

The range of the 8-bit hexidecimal numbers used in the Micro908 computer is ...

00, 01, 02, ... 09, 0A, 0B, 0C, 0D, 0E, 0F,

10, 11, 12, ... 19, 1A, 1B, 1C, 1D, 1E, 1F,

20, ...

30, ...

40, ...

50, ...

60, ...

70, ...

80, ...

90, 10, 92, ... 99, 9A, 9B, 9C, 9D, 9E, 9F,

A0, A1, A2, ... A9, AA, AB, AC, AD, AE, AF,

B0, ...

C0, ...

D0, ...

E0, ...

F0, F1, F2, ... F9, FA, FB, FC, FD, FE, FF

Where 00 = 0 Volts, and FF = 5 Volts.

Hence a voltage of '80' hex (halfway between 00 and FF) represents 2.5V

Another way to look at is is we have a 0-5V A/D converter with 256 steps (00 to FF), or 5/256 = 19.5 mV per step.

You can see that a number of C2 (hex) = 194 (decimal) by using the hex calculator in your Windows Accessories folder.

‘C2 steps’ then corresponds to a reading of 194 x 19.5 mV = 3.783 V

So when we say that "a reading of FF is too high and saturating the A/D channel", you'll know what we mean! ☺

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