SKTF -- Fall 1995

The Smith-Kettlewell Technical File

A Quarterly Publication of
The Smith-Kettlewell Eye Research Institute’s
Rehabilitation Engineering Research Center

William Gerrey, Editor

Issue: SKTF -- Fall 1995

Original support provided by:
The Smith-Kettlewell Eye Research Institute
and the National Institute on Disability and Rehabilitation Research

Note: This archive is provided as a historical resource. Details regarding products, suppliers, and other contact information are original and may be outdated.

Questions about this archive can be sent to


Connecting the Ohaus CT600 Electronic Balance to the Braille 'n Speak

Connecting the Oakton 59003-10 Ph Meter to the Braille 'n Speak

Accessing the Radio Shack 22-168A Multimeter with the Braille 'n Speak

The RF Applications P-2000CW Audible Power/VSWR Meter


by Dr. T.V. Cranmer,, David Lunney, et al.


These electronic balances are relatively inexpensive (in the $700 class), which means they are much cheaper than the "chain balances" we had in school labs. With an installable interface, they afford bidirectional communication with RS232C equipment.

[Editor's Note: Chemistry teachers yell at you when you call their fancy lab balances "scales." In this case, the term "scale" is correct; the units are weight-measuring devices, using strain gauges as force transducers. This means that for measurement of mass, you must calibrate them one way in Denver -- differently in New Orleans. (Not so for true balances.) Nonetheless, these Ohaus instruments are "just a pip" for accuracy; weighing a lock of your sister's hair is now possible, and an RS232C device can talk or Braille it for you. (This editor has not possessed and evaluated them directly, so attention must be paid to instruction materials provided with your scale and your access device.)]

General Description

The units in this series are rectangular, with a "pan" fitted to the top. This "pan" varies in size, depending on the unit. (For low-capacity units, the pans are round, flat "turntables" with no up-turned edges; for high-capacity units, the pan is rectangular.)

For connection to a computerized device, a $125 interface (added into the $700 ballpark figure mentioned in the abstract) is required. [Tim Cranmer assures me that the "interface," as you order it, is enclosed -- in the cabinet.]

I have been warned by Professor Lunney that the cable is critical. The output of the interface has one pin configuration, while the one at our end has another. A generic 9-to-25-pin cable will not work with the scale; you must use theirs. Given one of their cables with two 9-pin connectors, one must experiment. (Their cable is sixty bucks, also figured into the $700 price aforementioned.)

These units are actually weight-measuring devices; a calibration "mass" comes with each instrument. Holding down the "on" button for a few seconds puts the unit into the "calibration mode"; Tim Cranmer reckons that the succeeding procedures may require sighted help.

Interfacing to the Braille 'n Speak

Select the following communications parameters on the Braille 'n Speak:

  • Baud Rate--9600
  • Parity--none
  • Data Length--8
  • Stop Bits--1

Connect the BNS to the serial port on the Balance using the BNS cable number 5 from Blazie Engineering.

Commands for the Ohaus CT600:

(Note: Use only uppercase letters in these commands.)

[Editor's Note: Currently stuck with "literary Braille," there will be trouble afoot in presenting the following commands; for example, asterisks will appear here with spaces between, etc. We'll just let 'er rip, given that the rules are simple. Never are there spaces in the commands; two asterisks are to be considered "starstar." My separating double dashes are not to be entered; they are not minus signs. The final command, resetting defaults, is written out in words; when entering it, use no spaces.]

  • P--Print display data.
  • Question Mark--Print display units.
  • M--Units button.
  • T--Tare button (same as tare button on the front panel).
  • E--Extended units button (Same as pressing and holding the units button.)
  • *L--Start Linearity (Starts calibration procedure.)
  • *C--Start calibration (Starts span calibration.)
  • 0D--Turn off 1 second delay.
  • 1D--Turn on 1 second delay.
  • *0S--Turn off. Stable data only (Disables the stable data setting.)
  • *1S--Turn on stable data only (When enabled, the balance will send only stable data to the P command.
  • nnA--Set auto print interval (nn equals 0 to 99. Setting to 0 disables the auto print function.)
  • *0Z--Turn off auto zero tracking (Disables auto zero tracking feature.)
  • *1Z--Turn on auto zero tracking.
  • **V--print PROM revision level
  • **N--Disable automatic error message printing
  • Star Star Less-Than escape Greater-Than D--Revert to Factory Default Settings

[From Tim Cranmer]:

"Mr. Gerrey: Here is a note I sent to Deane Blazie, which includes information on where to buy the balance.

"The best balance I have been able to find has a capacity of 600 grams, just over one pound and five ounces. That's big enough for weighing a steak, fat letters and small packages for mailing, and specific gravity measurements for guys who want to make wine or beer at home.

"Did I tell you how to make a specific gravity bottle? You take one of those little single-shot whiskey bottles that you get on airplanes (plastic bottles are best). Pour the whiskey out, and fill the bottle with distilled water. Now, drill a tiny hole in the cap of the bottle, and carefully screw it back on the bottle. Weigh the bottle of water and write it down. Pour the water out and let the bottle dry.

"Now, when you are ready to measure the specific gravity of your homebrew, just dip the bottle in the batch (be dainty) and weigh the bottle. Divide the weight of the brew by the weight of the water, and there you are. Did I mention that you have to weigh the empty bottle with its cap? You would have figured that out."

Model Numbers and Ranges

The most-welcoming supplier is an old friend to SKTF, Cole-Parmer. (They take credit-card orders from individuals, and orders under $100 can still be had for a $5 charge -- no pesky minimum.) Furthermore, they are ready to take orders from overseas. The only trick is, they don't list, nor recognize, Ohaus numbers. Therefore, both numbers will be listed.

As far as power requirements are concerned, Ohaus offers mains adapters for 100, 120, 220, and 240 volts. As purchased from Cole-Parmer, units ending with a 0 are for 120 volts, and units with catalogue numbers ending in a 5 are for 220-volt supply. (Since the instruments are all running off so-called "wall-wart" power modules, the Cole-Parmer packaging is what you get with their catalogue number.) Thus, a 600-gram scale, No. E-11005-30, comes with a 117V power unit; an E-11005-35 comes with a 220V power unit.

Note that there is one instrument in this list that is designated "NTEP Certified"; then described as "certified for legal trade." This package is only available for 120 volts.

Ohaus Scales

  • CT10--Cole-Parmer No. E-11005-10, 10-gram capacity; readability of 0.002 gram, repeatability of plus/minus 0.002 gram, and linearity of plus/minus 0.002 gram; pan size, 1-3/4 inches diameter.
  • CT200--Cole-Parmer No. E-11005-20, 202 grams; readability of 0.01 gram, repeatability of plus/minus 0.01 gram, and linearity of plus/minus 0.01 gram; pan size of 4 inches in diameter.
  • CT600-Cole-Parmer No. E-11005-30, 602 gram; readability of 0.1 gram, repeatability of plus/minus 0.07 gram, and linearity of plus/minus 0.1 gram; pan size of 4-3/4 inches in diameter.
  • CT1200--Cole-Parmer No. E-11005-40, 1210 gram; readability of 0.1 gram, repeatability of plus/minus 0.1 gram, linearity of plus/minus 0.1 gram; pan size, 4-3/4 by 6-1/2 inches.
  • CT6000--Cole-Parmer No. E-11005-50, 6010 gram; readability of 1 gram, repeatability of 0.5 gram, linearity of 0.5 gram; pan size, 4-3/4 by 6-1/2 inches.
  • Cole-Parmer No. E-11005-12 (TEP Certified, "legal for trade"), 602 gram; same as the CT600, though not available packaged with the 220V power unit.
  • 77172-01--Cole-Parmer No. E-11005-80, serial interface unit.
  • ASO17-09--Cole-Parmer No. E-11008-83, 9-pin to 9-pin cable.
  • Other Ohaus Cables
  • 77609-01"Blunt-end user-defined cable.
  • ASO17-02--9-pin to 25-pin cable.

Address List

Cole-Parmer Instrument Company: 625 E. Bunker Court, Vernon Hills, IL 60061-9872; Phone: 1-800-323-4340.

Ohaus Corporation: 29 Hanover Road, Florham Park, NJ 07932; Phone: (201) 377-9000.


by T. V. Cranmer,

[Editor's Note: This paper is taken from the NFB/R&D list server, and it has become quite popular on the e-mail circuit.]

Greetings Colleagues,

The ph meter (Oakton 59003-10, available from Cole Parmer at $570) has arrived, and it looks like it is a good choice--even though it is not really bidirectional. For our demonstration purposes, it will do just fine.

Begin by setting the BNS parameters to match the defaults of the meter, as follows:

  • Baud Rate--9600
  • Parity--Even
  • Data Length--8
  • Stop Bits--1

The cable that came with the meter has nine pin connectors at each end. The Braille 'n Speak cable #5 mates with the Cole-Parmer cable, and makes the necessary jumper connections to work with the BNS and Braille Lite 18. After connecting the serial cable to the BNS through the BNS 5 adapter, the temperature and ph probes are plugged into their respective connectors on the meter.

Then plug in the AC adapter to the meter and the AC power outlet. The meter beeps to confirm that it has power and is ready for use.

There are seventeen easily discernible membrane switches on the top of the meter. These switches are arranged in a way that invites separation into two keypads. Twelve of the keys are in the configuration familiar to all users of the touch tone telephone.

The bottom right key, analogous to the pound sign on the phone, is the PRINT button, which must be pushed each time a reading is to be sent to the BNS.

Immediately to the left of this 12 keypad, there are five more switches in the shape of the grade II Braille "with" sign--dots 2-3-4-5-6. Dot 2 on this group of switches is labeled on/off, but it seems to do nothing more than enable and disable the PRINTfunction. There is no POWER on/off switch. One disconnects the AC adapter to power down the instrument.

Each time the PRINT button is pressed, a complete set of data is sent to the BNS or other serial device. The data are in the form: PH, TEMP, DATE, TIME, CR/LF.

It should be noted that key presses on the BNS are ignored. The same is true when using a computer to collect data with the software that comes with the meter. This is a shortcoming that could be troublesome for a student faced with the task of writing a program to monitor temperature and ph over an extended time period.

The next question is how the present collection of instruments can best be exhibited at the International Braille and Technology Center. I suppose we need to lay out a student lab station. Advice on how to do this is invited from any quarter. Thanks to David Lunney, Margaret Gemperline and Blazie Engineering for helpful advice and tangible contributions. We're not done yet.


By T.V. Cranmer,

Obtaining speech and Braille output from the Radio Shack Multimeter, Catalog number 22-168A, is the easiest task you'll ever find in these days of hi-tech instrumentation. Here are the steps to be performed:

1. Connect the serial cable provided with the multimeter to the jack on the side of the instrument.

2. Connect the BNS serial cable, type BNS5, to the end of the multimeter serial cable.

3. Connect the BNS cable to the serial jack on the BNS.

4. Set the communications parameters in the BNS to 1200 baud, 8 data bits, 2 stop bits, and enable the serial port.

5. Turn on the multimeter.

That's it. Just tap the space bar on the BNS any time you want to read the multimeter display. (I like to turn on "interactive mode" of the BNS so that each reading of the meter is spoken immediately, as well as the last readings in the current line.)

If you want the BNS to continually speak meter readings, make a macro by pressing chord n, then press a key to identify the macro (like m for meter), then press chord j to j followed by the letter m. This causes a continuous loop that obtains and speaks the information on the multimeter display. This can be interrupted only by turning the BNS off.

You should, of course, open a file on the BNS when using it to capture meter readings. I have been using the clipboard for this purpose.

I also find it very helpful to secure the multimeter, along with its serial cable and test leads, to a metal plate large enough to allow the BNS to sit. This arrangement permits easy moving of the talking meter around the house and workshop as needed.

The multimeter is about as complete as anything I have seen for use by electronic engineers and hobbyists. Here is a brief description:

Radio Shack Multimeter, Catalog number 22-168A. Just below the display, there is a row of 4 pushbuttons. From left to right, these buttons are: Power on/off; Function; Set/reset; DC/AC. The power button toggles between on and off. The function button scrolls through several special functions, such as setting off-set, storing values in memory, etc. The set/reset switch enables and resets various selected functions, such as max/min readings. The last button in this group toggles between AC and DC when measuring current and voltage. The default is DC.

Immediately below, there are two more buttons. From left to right: Up; Down. These buttons are used in conjunction with various functions, such as setting offset voltage measurements, storing readings in memories, etc. A dual transistor socket is located to the right of these two pushbuttons.

A set of clips for holding capacitors is located on the right edge of the front panel below the transistor sockets.

Along the bottom of the front panel, there are four banana jacks. These are labeled, from left to right: 20 A; mA; COM; V/Ohm.

The RS232-C connector is located on the right side of the meter, near the bottom--just a little above the position of the right-most banana jack.

Functions selected by the rotary switch: With the rotary pointer positioned just below three o'clock, the instrument is set for the lowest voltage range. Rotating the switch clockwise selects functions and ranges as follows:

  • 200 mV
  • 2V
  • 20V
  • 200V
  • 1000VDC, or 750VAC

Starting just before 6 o'clock:

  • 200uA
  • 2mA
  • 20mA
  • 200mA
  • 20A
  • Two notches below 9 o'clock: (Frequency) 2kHz to 20MHz
  • One click below 9 o'clock (Transistor function): hFE
  • One click above 9 o'clock (Logic function): displays High, Low, undetermined.
  • Two clicks above 9 o'clock: Continuity checker.
  • Three clicks above 9 o'clock: Diode checking, use the probes.

Four clicks above 9 o'clock begins the resistance ranges:

  • 200 Ohm
  • 2000 Ohm
  • 20K Ohms
  • 200K Ohms
  • 2 Megohms
  • 20 Megohms
  • 2,000 Megohms

Continuing to rotate clockwise brings us to two clicks above three o'clock (Low capacitance):

  • 200 pF to 200 nF
  • 200 nF to 200 uF


Reviewed by Tom Fowle, WA6IVG

[Note: We would like to thank Gary Jackson, KK5GE, of Grove, Texas, for alerting us to this instrument's existence. Before now, we have recommended using a "noise bridge" as a substitute; we could only offer circuit diagrams of our audible meter readers as do-it-yourself adaptations to visual VSWR meters.]


This excellent unit fills perhaps the most often requested need for accessible equipment. The meter allows both digital and "simulated analog" measurement and adjustment of power output and VSWR (Voltage Standing Wave Ratio) of medium-power radio transmitters (such as amateur-radio equipment) operating between 1.5 and 30 MHz. Quantified readings are issued in Morse code, while dynamic adjustment of relative power and VSWR are made possible by audible indications to be described.

General Description

The instrument consists of two sections: the sensor or "bidirectional coupler," and the "meter," or Morse code readout box. The sensor unit is connected via standard "PL259" connectors between the transmitter or transceiver and the antenna. If an antenna tuner is used, the sensor must be connected between the transmitter and tuner to see its desired 50-ohm impedance. The sensor is connected via two cables equipped with BNC connectors, to the readout box.

The readout box needs to be supplied with 12 volts DC at about 100mA via a standard coaxial power connector, cable supplied. Although there is no tactually determinable marking on the cable for polarity, the shell of the coaxial power plug is negative, and a quick check with your continuity checker will let you mark this negative power lead to avoid wrong polarity. (The circuitry is equipped with a protection diode in the power input, so if you reverse the power connections, the diode should protect it from damage.) The readout box also contains an earphone jack.

Two RCA jacks which connect to the contacts of an internal relay are provided; these contacts may be connected in the keying line of a power amplifier, and the unit can be set to open these contacts when the VSWR exceeds a preset point. Thus it can automatically monitor your VSWR and shut down your kilowatt amplifier before meltdown.

The sensor box is a dye cast aluminum case having two SO239female connectors on one side, and two BNC connectors on the other. There is also a nice No. 10 ground screw between the two BNCs. A substantial mounting plate is provided in back of the SO239's.

Holding the coupler box with the antenna connectors up, and the mounting plate away from you, theSO239 to the right is labeled "antenna," and the one to the left is "transceiver." The BNC connector to the right is labeled "forward," and the one to the left "reverse."

The readout unit is an aluminum case about 8 inches wide, 3 inches deep and 1-1/4 inches high. The front panel of this cabinet holds a pushbutton at either end and two pointer knobs nearer the center. The left button activates the power readout, and the right button calls for a VSWR reading. The left knob adjusts Morse code readout speed, and the right one adjusts volume.

Holding the readout unit with its rear panel facing you, the BNC connector at the left end accepts the cable from the "forward" connection on the sensor, and the second BNC from the left is for "reverse" power. Immediately to the right of the "reverse" input connector is the 1/8-inch earphone jack.

To the right of the earphone jack is a tiny pushbutton followed by a small hole allowing access to a screwdriver-adjust trim pot inside the box. These are used in setting the "overload" preset point as described later.

To the right of the potentiometer access hole is the coaxial power jack appearing through a square hole in the case. To the right of this power jack are the two RCA jacks; the center contacts of these jacks go to normally closed contacts of an internal relay for connection to the keying line of an amplifier.

The BNC cable which is connected on the directional coupler closest to the antenna cable is the one providing the forward power information; it should be connected to the socket nearest the end of the readout box. It apparently makes no difference which way around the sensor unit is placed in the transmission line; as long as the signals going to the readout box are correct, the readings will be good. No harm is done if things are hooked backwards--there will simply be much more reverse power shown than forward, and thus the VSWR will always be exceedingly high.

Since the unit measures the RF voltage only, the accuracy of its readings, and in general the meaning of them, is dependent upon a good 50-ohm match. Thus, when the VSWR is wrong, that is all you know--and the worse it is, the less you can rely upon the actual readings.

An internal microprocessor calculates the power reading using the E squared over R formula, and since there is no system here for measuring R or system impedance, the calculation is only correct when there is a good match. Thus the VSWR readings must be thought of as relative only, and power numbers only have use when the VSWR is very low. This does not degrade the usefulness of this instrument in the least; using it, the operator can easily adjust an antenna for a good match and check the power output.


The manual suggests that the readout unit be powered up to check its operation before further connections are made. Connecting a 12-volt source to the supplied cable (with the negative supply going to the connector's outer shell), the unit will send "RFA" in Morse shortly after being powered up. Pressing the left button will get "0 W" for 0 watts, and pressing the right button will get "1 r 0" for one point zero VSWR. Note the use of the character "r," which is the decimal point in International Morse.

The two reading buttons can be repeatedly pressed now so as to allow for adjusting speed and volume with the two knobs.

Next, connect the coupler unit between your transceiver or transmitter and the antenna or tuner using appropriate coaxial jumpers. A substantial ground wire as short as possible is recommended to be hooked from the ground screw on the coupler to station ground.

Connect the two BNC-equipped cables between the two units, seeing that the cable connected opposite the antenna connector goes to the "forward" connection on the readout box (nearest the end) as described above. The manual describes one of these cables as "red," and that one is suggested to be used for forward power. The "red" cable has small wraps of red tape which can be felt just behind the connectors. This has no electrical significance, but if you have sighted help, confusion will be minimized.

For first experimentation, it is wise, and civilized, to attach the system to a dummy load so as to avoid causing unnecessary interference while fiddling around with the meter. This will also let you be sure things are working correctly, since your dummy load is more likely to present a 50- ohm match than would be gotten with your sky wire or fence post.

When you power up your rig, and press the SWR button, you will hear the Morse readout of the two-digit number with the digits separated by an "r" for the decimal point. If you're using a dummy load, you will most likely hear "1R0" or "1R1," giving you a substantial indication that things are fine. Now pressing the left "power" button will get you a power reading; in the case of most modern transceivers, this will probably be about 100 watts, "100W". The unit can produce indications up to 9.9 to 1, but as suggested previously, these kinds of numbers have little meaning.

The P-2000CW can produce "simulated analog" readouts of both power and VSWR. These are most useful when making adjustments--for example, when adjusting a tuner.

The analog ("qualitative") indications are initiated by first keying your transmitter, then pressing and holding the button corresponding with the reading you want.

For example, pressing and holding the VSWR button for about two seconds gets you a Morse "R" (for "roger"), indicating that the analog simulator is active. When you release the VSWR button, the unit emits a series of beeps whose rate is inversely proportional to the VSWR; in other words, the faster the beeps, the lower the VSWR. When the reading is below 1.3 to 1, the tone becomes steady. Thus you can tune your antenna tuner for faster beeps or a steady tone, which provides a much faster means of adjusting for a match than repeatedly listening to Morse code numbers.

In like manner, the power analog indication is started by keying the rig, then pressing and holding the left "power" button for about two seconds. This produces a Morse "R," and when the button is released the unit emits a rather "buzzy" tone whose pitch varies relative to the forward power seen in the coupler. This can be quite useful in "peaking an amplifier" (tuning up a rig made in the days when you could warm your hands on it). This mode is also nice for setting the drive level control on modern transceivers so as to find the point where maximum power output is just achieved. It can also be helpful when making a first quick coarse adjustment of a tuner, letting you know that the match is at least good enough to let the transmitter provide some power before doing the fine tuning using VSWR readings.

Analog indications stop either when the button is pressed a second time or when RF power is removed. When this happens, the unit sends "OK" to let you know that it is back to normal.

Since the analog system quits when the unit is not seeing more than 2 watts of RF, adjustment of low-power transmitters using the analog system can be difficult if the VSWR gets so high as to cause the transmitter to "fold back" to less than 2 watts output. The unit sends "OK" when the analog system drops out.

Automatic Overload Indication

The P-2000CW can automatically tell you when your VSWR has reached a settable level. This level is set by the factory at 3 to 1, the point at which most modern transmitters substantially reduce power output to protect final amplifiers from heat buildup caused by high reflected power. When the VSWR is over 3 to 1, the unit sends Morse "V" continuously, and also opens an internal relay. This relay's normally open contacts can be connected between the "push to talk" line output of your transceiver and the keying input of a power amplifier, thus automatically shutting down the amplifier before damage is done. The normally open contacts of this relay are brought to the center pins of the two RCA jacks on the rear panel of the readout box.

The overload level can be adjusted by placing a small screwdriver in the aforementioned hole on the rear panel of the readout unit and adjusting the internal pot. Pressing the very small pushbutton next to the adjustment causes the unit to send the level at which the overload system will activate. The factory default is 3 to 1, so simply pressing the button without fiddling around with the adjustment will confirm that the factory setting is as expected.

Even if you're not using a power amplifier, this automatic indication can let you know that, for example, you've forgotten to change antennas when changing bands, or you've forgotten to reconnect something after the last storm.

Internal Jumpers:

Several parameters for the readout can be changed via a set of jumpers located inside the readout box. First, and most interesting perhaps, an "abbreviated" Morse code can be selected in which the number 0 is replaced with the letter "T," the number "1" is replaced with "a," and the number "9" is replaced with "n." This system noticeably speeds up the Morse output in many cases, and soon seems familiar to the CW user. Thus, with this option selected the common VSWR reading of 1.1 to 1 is heard as "ARA," and the also common power reading of 100 watts is heard as "ATTW." (Neat thinking, guys!)

The second internally settable option involves the readout resolution. With the factory default, the P-2000CW will send power readings with maximum available resolution. If the internal jumper is changed (see below), the power will be reported in 10-watt increments.

A third jumper-selectable option changes the "side tone," or Morse output frequency, from the default of 700Hz to 1000Hz.

Accessing these jumpers involves opening the readout cabinet. Although this is not particularly difficult, it lets loose quite a few nuts and bolts that you can easily lose, so have a small container handy when you do this job and be sure to put things in it. I repeat this perhaps obvious warning because we in the lab didn't do it right off, and were almost sorry!

To open the cabinet, remove two sheet metal screws from the top of the rear apron and two more from the front of the bottom of the box just outboard of the front rubber feet. Now remove the bezels and button caps from the pushbuttons by gripping the tapered bezels with thumb and finger and unscrewing them. The button caps will most likely come with the bezels, and are candidates for flying off in all directions.

Finally, you must remove the pointer knobs with their small slotted set screws, and remove the holding nuts and lock washers from the two pot bushings. Warning: things get a little greasy here--have a paper towel handy.

Now you can slide the top, front and sides of the case forward and lift this part of the housing off. Be careful of the buttons and pots--they are held on only by their leads soldered into the board.

Jumpers--Their Location and Layout:

There are two groups of jumpers on the board, both located near the 20-pin skinny-dip package in a socket near the right edge of the board. By the way, this 20-pin chip is the microcontroller, a Microchip PIC16C73. Just to the left of this chip and near its bottom end is a 3-pin jumper block oriented with its long axis parallel to the axis of the micro. This is the so-called "A/B selector," which sets the side tone frequency. With the jumper in its factory default "up" location, the B jumper is selected, giving a 700Hz side tone. When moved to the lower two pins, the A selection of 1000Hz is made.

To the right of the 20-pin microcontroller is a 9-pin jumper block in a 3 by 3 matrix. The three pin rows here run left/right perpendicular to the axis of the micro. The top set of 3 pins is the "C and D selectors"; with the jumper in the default (right) or "D" position, full Morse code is selected. With the jumper moved to the left ("C") position, abbreviated Morse is selected. We strongly recommend this change since it substantially improves overall reading speed.

The second (middle) row of 3 pins in this matrix are the so-called "E and F selectors," which control readout resolution. With the factory default F (right) position selected, full resolution of the microcontroller's 8-bit analog-to-digital converter is reported. When the left-hand ("E") selection is made, resolution is limited to 10-watt steps. This means that the final digit of any power reading is always reported as 0, such that 101 watts is the same as 109 watts.

The lower set of jumper pins is not used, although a factory default jumper is placed on the right set of 2 in this row. One might suppose that this is a test jumper; however, no attempt was made to determine if moving it has any effect.


  • Frequency Range:--1.8 to 30 MHZ;
  • Line Impedance--50 ohms;
  • Power Range--2.5 to 2030 watts;
  • VSWR Range--1-to-1 to 9.9-to-1;
  • Accuracy--plus/minus 10%;
  • Reading Capture Time--100 milliseconds;
  • CW Speed--5-to-45 words per minute;
  • Audio Output--1 watt;
  • VSWR Alarm--minimum 1.0-to-1, maximum 10-to-1;
  • Relay Contacts--1 amp, 24 volts DC;
  • Maximum Drop-Out Response Time--less than 200 milliseconds;
  • Power Required--12 volts, 200 milliamps.