Q: Explain MB-1's different Power Measurement Modes

In Amateur Radio applications, it is useful to be able to measure peak power, average power, and instantaneous power of the forward power signal.  Most of the popular digital Amateur RF power meters on the market do not measure all three of these modes. For example, the PowerMaster has only one forward power mode that can be displayed in numerical form - namely peak power. And while some of the other digital RF power meters on the market claim two power measurement modes, an experiment is proposed below that tests those claims when using those meters in a typical amateur radio operating environment.

On a properly tuned transmitter, the peak power should be close to key down power, or slightly higher due to the ability of the transmitter's power supply to recover during syllables or code elements. But peak power tells you very little about your talk power. A meter that provides a numeric readout of peak power only will not give you an accurate indication of talk power.  (In fact, a peak reading meter will give you approximately the same reading with your compressor on and off even though there may be a significant increase in talk power with the compressor is turned on.) To measure talk power, you need a meter that measures average power over a reasonable sampling interval (more on that below). And for reasons described elsewhere, you can not get a consistent view of of your talk power using the autoranging bar graphs on the other meters.

And why instantaneous power? Instantaneous power is most useful during transmitter, amplifier, or antenna tuner adjustments where it is desirable to have the meter's readouts respond "instantaneously" as adjustments are made by the user. It is also useful for following your voice modulation or keyed CW in real time.
 

MB-1 can measure peak, average, and instantaneous forward power, and can display all three modes simultaneously if desired on its numeric displays, its bar graph, or its analog meter, at your discretion.  

Some additional comments on average power and instantaneous power measurements:
Peak power is straightforward, but some comments on average and instantaneous power are warranted because these terms are sometimes used imprecisely.

Average power: An important parameter for average power measurements is the period of time that the signal is averaged. This depends on the application, but in our opinion, to be meaningful for Amateur Radio, the period should be at least as long as a few syllables for voice, or as long as a few dits and dahs for CW - let's say from a couple of tenths of a second to several seconds.

Instantaneous power: As its name implies, instantaneous power measurements are a series of  "snapshot" measurement in real time, ideally with a rapid update rate when used with a responsive display devices such as an analog meter. For the most responsive measurement, the meter should follow the actual real time signal being measured (within the capabilities of its sampling speed) with no hang time or over-sampling.

 

Verification:
To determine if a meter can measure and display average power on its numeric display, consider the following experiment. If the meter has an "Average" mode, select it. With the meter inserted in line, tune up into a dummy load with a known key down power level (for example, 100 watts). Then using a keyer, send a series of dits at various speeds. The generated "dit" signal should have an approximate 50% duty cycle. Therefore, after a short time, the average power reading displayed on the numeric display should read  approximately 50% of the key down power. Then send a series of dashes at various speeds.  The generated "dashes" signal should have an approximate 75% duty cycle. With the dashes applied, after a short time, the numeric display should read approximately 75% of the key down power. If the measurement from the meter under test bounces erratically without converging, or if the measurement deviates significantly from  the expected values, then, in our opinion,  the meter under test is not providing a useful indication of average power as defined  above. 

If the meter under test can measure instantaneous power, the majority of the measurements from a keyed CW signal (dits or dahs) should read either the key down power (100 watts in this example) or 0 since the keyed CW waveform is alternating between these two power levels. (Since keyed CW has a finite rise and fall time, an occasional measurement may occur at the transition, sometimes yielding an intermediate value.)  If the numeric display on the meter under test reads neither 0 nor the approximate key down power for the majority of its measurements, it is not measuring instantaneous power as defined above. 

To measure instantaneous power,  MB-1 samples the signal at a very high rate (up to 500 times per second) and displays the measurement for the display interval set by the user. When set to the maximum update rates, MB-1's bar graph and analog meter are being updated every measurement cycle. This is why MB-1 can capture short term dropouts and spikes.

To measure average power,  MB-1 accumulates and processes all samples in a .3 second to 8 second sliding window (depending upon how the user has configured MB-1's averaging filter) to arrive at an average power measurement. 

Confused?  MB-1's definition of instantaneous, peak, and average power are explained above, and hopefully, appear reasonable to you. Simply stated, MB-1 can display any of these three power modes on any of MB-1's display devices.

 

Q: What benefits will I see with MB-1's Digital Filtering?

When displaying instantaneous or average power with a constant power level applied, you will see a stable measurement with virtually no jitter. Likewise, if you key power on and off multiple times with the key down power set to a fixed value, you will see the same measurement (within a very small delta).  If you do A/B comparisons between MB-1 and the other digital meters that are capable of displaying instantaneous or average power on the display head, you will see the differences in both stability and repeatability.
 

Q: You use the term "Measurement Cycle". What is that?

A measurement cycle is the basic processing unit of the MB-1 software. Each measurement cycle includes adjustment of the Programmable Gain Amplifier to maximize the resolution for the current sample, acquisition of the gain-adjusted A-to-D measurements from the forward and reverse coupler ports, processing of  those measurements (e.g., digital filtering, SWR Trip processing, etc.), and finally display of the measurement values on the display devices using the selected display update rates. This process repeats indefinitely unless interrupted by a user request, such as when a menu button is pressed to change a meter setting. Depending upon how the meter is configured, the MB-1 Measurement Cycle time can be less than 2 milliseconds.

Q: What is the significance of 15 bit low range resolution?

At the lower power ranges where resolution is more critical, 15 bit resolution provides smaller step sizes, and therefore better resolution. Since the maximum (full scale) digital output of the MB-1 Amplifier/D-to-A chain is 32,768, 1 count represents a signal whose voltage is 1/32,768 of the full scale voltage (the voltage generated by the coupler when full scale power is applied). And since MB-1 operates its A-to-D chain at the voltage level and not the power level, the one part in 32,768 becomes one part in (32,768)² when determining the smallest power step size that can be resolved.

For example, consider a coupler with a full scale power rating of 10,000 watts (a value used others when discussing this topic). When calibrated with MB-1, such a coupler would generate the maximum count (32,768) at full scale. Therefore, the smallest power level that can be detected by MB-1 occurs when the A-to-D chain generates a single count. This corresponds to 10,000  * (1 /  (32,768) ²⁾ , or 9.3 microwatts. (In reality, because of the A-D noise floor, a more realistic number is 50 microwatts.)

You may make the valid observation that this value is somewhat meaningless since MB-1 display devices show only two significant digits after the decimal point. That's a valid point, but when the software is working with microwatt power per step, on a carefully calibrated coupler, you can have confidence that low power readings, when rounded to two significant decimal points, are meaningful.

To address this loss of resolution problem at low power levels, some of the other meter manufacturers offer multiple couplers for the same bands that primarily differ in their sensitivity. MB-1's 15 bit resolution makes this unnecessary.

Q: You use the term "Averaging Window" for Average Power Measurements. What does that mean?

For average power measurements, you can set the averaging window from .3 seconds to 8 seconds. You can think of this in terms of filter response and time constants. The digital filter time constant for average power measurements is set to one fifth the averaging window (resulting in the averaging window being equal to approximately five time constants). Therefore, if you apply a step function such as a 100 watt key down signal, if the averaging window is set to 5 seconds, the average power value will read to within 1% of the final value (100 watts) approximately five seconds after it is applied.
 

Q: Why no temperature compensation?

Some other meters that incorporate  "logarithmic detector" chips in their design can benefit from temperature compensation. The MB-1 is essentially immune to the type of temperature drift encountered in those designs.

 

Q: 30,000 watts? Are you kidding me or what?

The data types and software algorithms used in the MB-1 software max out at approximately 32,000 watts, so it was decided not to artificially limit the measurement range to a lower number. A high power coupler, when calibrated in accordance with the manual, should work properly.  Also, with the Generic Meter Application feature, depending upon the analog sensor and type of application, the maximum full scale value of a target parameter can be just about any value, so the larger range has value for those applications.

But to answer the question - has MB-1 been tested at 30,000 watts? Only with the simulator.

 

Q: What is the SWR Stabilizer Feature?

Many of the popular digital power meters do not provide a stable SWR indication for time varying signals such as SSB.   This is especially true if the meter incorporates a rapid response display device such as the analog meter or bar graph.  Since the SWR is independent of signal level, this behavior is usually a limitation in the meter, and not a result of the SWR changing with the time varying signal.

MB-1 can provide a stable SWR value for time varying signals. This is accomplished by using digital filtering on successive SWR samples. When the algorithm determines that it has arrived at an accurate SWR value, the digitally filtered value of the SWR is displayed. In most cases, even short duration signals, such as a whistle, a lip smack, or even the keying noise from most microphones PTT buttons, will display a stable SWR value and hold it long enough for you to read it comfortably.

Note that this is not a simple "display hold" feature. For example, if, while sending a CW signal, you change the SWR of the load, you will see the new SWR displayed on MB-1.

Q: What is the "Snap Measurement to Constant Signal" Feature?

You can configure the meter to snap (lock) the average measurement to what would have been its final value when a steady state (constant) signal is detected. An example will help explain how you might use this feature.

Assume that you have configured the meter to display average power on one of the display devices such as the analog meter. Assume also that the averaging window has been set to a long window (e.g., 8 seconds). If you place your equipment in a tune mode (which generates a constant signal),  it will take approximately 8 seconds for the average measurement to reach its final value. If you have the snap feature on, as soon as the software detects that the level of the input signal is constant, a user configurable timer will be started. After that timer elapses, the average value will lock or “snap” the average measurement to the current steady state power level that is being applied. This allows you to view the actual average power for normal operational conditions such as a voice or CW signal, while giving you a quick, stable response to a constant signal, as would be encountered when tuning your transmitter.

You will find this feature useful if you have remotely located an analog meter next to one of your stations away from the control head. Since you can only display one parameter at a time on an analog meter, choosing to display the average power value with the snap feature enabled provides you the advantages discussed above. You can turn the snap feature off completely if desired.

Q: Digital Filtering for Instantaneous values? That doesn't make sense.

The Forward and Reflected power measurements are processed in parallel as a both a snapshot values (the true instantaneous values), and as filtered values. When the signal is varying, the snapshot values are displayed. When the software determines that a steady state signal is present, the filtered versions of the measurements are displayed. When a steady state signal is applied, such as during tune-up, this almost completely removes any jitter from the displayed values and results in extremely stable and repeatable measurements.

Q: How Does the Peak Hold Algorithm work?

Each time a measurement is processed,  the software checks the value of the current peak power, and if it is higher, the peak power is updated to the new value. The peak hold timer is then reset. Assuming that the no power measurements exceed that last  peak power measurement for the peak hold interval, the peak hold timer will time out, and the new peak power value will be set to the current power level, regardless of its value. For SSB, for instance, if the peak hold is set to 1 second, and you stop transmitting, the peak power will drop to 0 within 1 second or less, depending upon when the last voice peak occurred with respect to the end of transmission.

Q: What Reference is used to calibrate the Assembled MB-1 units?

A MiniCircuits PWR-6GHS Power Sensor is used. This is a NIST traceable device.

Q: Can I calibrate other power sensors using the MB-1 as its own reference?

Yes.  You can use one of the following approaches:

1. Voltage Measurements: Place the MB-HF1 coupler in series with the coupler being calibrated, and use the approach described here.

2. Power Measurements using MB-1 and the MB-HF1 coupler: Place the MB-HF1 coupler in series with the coupler being calibrated. For this discussion, assume that the MB-HF1 is connected to coupler port 1 and that the coupler being calibrated is connected to coupler port 2. Also assume that you want to calibrate your coupler at three points (5 watts, 100 watts, and 500 watts).  The following lists the steps that are required for each point:

        1. With the MB-1 in its normal (measurement) mode, set your transmit power to 5 watts.
        2. Remove transmit power.
        3. Enter Setup, select coupler 2 and place it in the calibration mode.
        4. Select the 5 watt calibration point using the Setup procedure, apply power, and save the calibration point.
        5. Terminate the calibration for the coupler and save the calibration settings.
         (At this point, coupler 2 is calibrated, but your calibration table has only one calibration point).

Repeat the above steps at the 100 watt level. This time, when entering the calibration setup for coupler 2, pick the EDIT mode, which allows you to change, add, or delete previous calibration points. When done, save the settings for coupler 2.

Repeat the above steps at the 500 watt level. As above, when entering the calibration setup for coupler 2, pick the EDIT mode since you will be adding the 500 watt calibration point to the previous two calibration points.

 Depending upon your coupler, three points may be adequate. Remember that this is not a simple lookup function. Each calibration point is used to calculate the best Power vs. voltage curve when the current power is in the vicinity of that calibration point. An ideal coupler (one that follows the Power vs. V² relationship) would need a single calibration point.

Check the new coupler's calibration against the MB-HF1 by applying power, and switching between coupler 1 and 2. If you see a range where the tracking can use improvement, simply add a calibration point at the affected range. (If you are interested in QRP operation, low power accuracy will probably benefit by adding a couple of calibration points in the 0 - 1 watt range.)

Once you are familiar with the MB-1 operation and the coupler calibration procedure, each calibration point can be done in a minute or so.
 

 

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Couplers

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Q: How do I know if my coupler will work with MB-1?

After you have used the coupler calibration setup routines a few times, you can do a reasonably quick calibration with your coupler and simply try it out. If you want to do some stand-alone testing of the coupler first, this link has the details.

Q: Regarding Support for multiple couplers, do all the couplers have to be the same type?

No. Each coupler is calibrated independently with its own calibration table. You can mix  HF, VHF, and UHF couplers.

Q: What frequency range does the MB-1 cover?

There is no restriction. If you have a Bruene type coupler with DC outputs that meet the interface requirements, you should be able to interface it to MB-1.

Q: What are the coupler requirements?

MB-1 can adapt to a wide range of Bruene type couplers. For couplers whose full scale power produces a DC voltage greater than 6 volts, resistive dividers (15 turn pots) are provided in the MB-1 Amplifier/Mux chain to scale the voltage down to prevent overdriving the Amplifier/A-to-D chain used in the meter. For best resolution and accuracy, the coupler should put out a DC voltage of 6 volts or more. This is not a problem for most couplers. MB-1 will work with coupler with lower sensitivity but at a reduced resolution. For a more detailed discussion, see the section on User Couplers.

 

Q: Can I use the LP-100 Couplers with MB-1 ?

No. The LP-100 couplers provide voltage and current samples instead of forward and reflected DC outputs voltages, which are found in Bruene type couplers.
 

Q: How is the MB-HF1 Coupler Baselined?

A Bird 4391A RF Power Analyst is used for the couplers supplied with the MB-1 kits. Couplers supplied with assembled units are also baselined at the factory using the Bird 4391A, but the final coupler/MB-1 calibration is done with a MiniCircuits PWR-6GHS Power Sensor, which is a NIST traceable device.

Q: Can I integrate the MB-1 into an Antenna Tuner and use the MB-1 for power and SWR measurements instead of the tuner's meter?

For a manual tuner - Yes. Just connect the coupler connections from the tuner to one of MB-1's four coupler ports. To use an analog meter when integrating MB-1 with your tuner, you have two choices. You can use MB-1's internal analog meter (or any other external analog meter you have connected to MB-1). Or you can drive the Antenna Tuner's analog meter as an external Panel Meter from MB-1. Just use the standard MB-1 procedures for adding and calibrating external couplers and Panel Meters. If you integrate MB-1with your tuner, all of MB-1's features, such as SWR trip and Min/Max are available.

For an Automatic Antenna Tuner - Not Recommended.  This is not recommended for Automatic Antenna tuners unless you are sure that the input impedance of the coupler ports (300 K), when placed in parallel with the tuner's measurement circuitry, will not affect the tuner's operation.

 

Q: You do not have a setting for band correction for 1.25 meters. Can I calibrate my 1.25 meter coupler and save the settings for a band I am not using?

Yes. The 160 meter - 70 cm titles used by the software are just place holders for separate sets of band correction factors stored in the EEProm calibration tables.

 

Q: Can the meter read powers lower than the lowest calibration I calibrated the coupler at, or higher than the highest calibration point I calibrated the coupler at?

Yes.  This is accomplished by using the calibration data for the lowest or highest power level at which the coupler was calibrated. The meter can also read power levels higher than the full scale value for which the coupler was calibrated at as long as the input voltage at the coupler input does not saturate the MB-1 Mux/Amp. The normal calibration routine includes steps to ensure that saturation will not occur at or below the full scale power.
 

Q: While experimenting with the Band Calibration feature, I switched between the Reference Band and a Band that I performed frequency correction on while keeping the frequency and power of my transmitter constant. As expected, when I switched bands using the Band menu, a different power value was displayed. But if I take the ratio of these two power measurements, it does not agree with the real time band correction value being displayed in the Correction field of the Band Menu.

That is because the Correction Factors, which are calculated during calibration, and applied during operation, are done at the voltage level, not the power level. If you take the ratio of the square roots of the two different power measurements, this should equal the real time band correction factor value that you are seeing displayed in field 2 of  the Band menu.

For example, assume that you have done the reference band calibration on 80 meters, and that you have also performed band correction on the 6 meter band during calibration. For this discussion, assume that the coupler is more sensitive on the 80 meter band (for a given power, it will produce a larger DC output voltage when the operating frequency is in the 80 meter band than it will when operating on the 6 meter band for a given power level). In this case, you would expect to have a positive correction factor (the ADC value measured when operating on the 6 meter band needs to be adjusted upward to give the corrected power value).

Repeat your experiment as follows: Take a coupler that has been calibrated as above, apply a signal on the 80 meter band, and then change the band on the MB-1 Band menu without changing the transmitter power or frequency. You should see that the power reading displayed by MB-1 with the band set to 6 meters is a larger power value.

Using some numbers, assume that you measure 20 watts on the 80 meter band, and measure 21.22 watts when you switch the band to 6 meters using the Band menu. In this case, the correction factor (which will be displayed on the Band menu on Line 4 of the LCD) should be = sqrt (21.26) / sqrt (20) = 1.031.

If you have performed band correction at more than one power level on a given band, the power correction factor will be recalculated for every measurement using interpolation of the available band correction factors. Therefore, if you vary the power between two or more power levels that you performed band correction on, you will see the value of the displayed correction factor change to an intermediate value as you vary the power.

Of course, the idea here is to give you the correct value when you actually do switch your transmitter to another band. Hopefully, the above explanation will help you understand how band correction is accomplished by the software.
 

 

Q: What is the OEM Calibration Table Update Utility used for?

MB-1 comes with a factory loaded calibration table for the MB-HF1. We hope to include calibration tables for other popular couplers as well.

Couplers in this table are assigned an OEM code that can be used to simplify coupler setup if you are interfacing to one of the supported couplers. The calibration tables for OEM couplers are loaded into the "OEM" section of EEProm. These OEM coupler tables can be easily  loaded into one of MB-1's four coupler tables (coupler 1 - coupler 4) during coupler setup by specifying only the OEM code (see User's Manual).
 

The OEM Calibration Table Update Utility allows you to get the latest set of calibration tables from the MeterBuilder website  by downloading a data file. That data file is then used to update the OEM table section of MB-1's EEPROM using the OEM Calibration Table Update utility developed by MeterBuilder.

MeterBuilder will update the OEM calibration tables as we add support for additional couplers. The calibration tables will also be updated if we improve the existing calibration tables for any reason (for example, by adding additional band correction points at more bands for previously supported OEM codes including the MB-HF1 coupler).

Of course, for maximum accuracy, you always have the option to do a full custom calibration on any Bruene type coupler, including the ones supported in the OEM tables. However, the factory loaded calibration tables simplify this process since you only have to specify the correct OEM code during calibration (thereby eliminating the need to do the point-by-point calibration). If you use the OEM setup procedure, the only additional adjustments required are the FWD and REFL side panel trim pot adjustments, which need to be adjusted at a single power point as described in the User's Manual.

 

Q: If my coupler's FWD-to-REFL tracking is poor, can I calibrate each port independently to get accurate reflected power values?

Based on our experience, this is not required for most couplers. But each port can be calibrated independently if desired. You can view this as analogous to the BIRD meter mode of operation where you reverse the slug to read /forward/reflected power.

Simply calibrate the FWD port of the coupler using one of MB-1's four coupler ports, and calibrate the REFL port of the coupler using a second MB-1 coupler port. Connect both the FWD and REFL DC outputs from the coupler to the FWD port of the two MB-1 coupler ports being used. Leave the REFL input of each of the two MB-1 coupler ports unconnected.  Turn the REFL port trim ports on each of the two MB-1 ports being used in this mode to their maximum CCW (minimum sensitivity) setting.

To use a coupler configured this way, use the coupler menu to select the MB-1 coupler  connected to the coupler's FWD port to read FWD power.  Use the coupler menu to select the MB-1 coupler connected to the coupler's REFL port to read REFL power. 

Of course, analogous to the BIRD mode of operation, this requires that you calculate the SWR manually (easily done with this online SWR calculator). But in many cases, when you are reading REFL power, your primary concern is minimizing the REFL power, with a lesser emphasis on its absolute value.

 

 

Q: The power rating on the coupler label is different than the value listed in the Specifications. Which is correct?

The more conservative values in the Specifications section are correct. The label will be changed in the next run.

 

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Bird Line Section and Meters

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Q: What advantages does an MB-1/Bird Line section arrangement have to a Bird type 43 wattmeter?

With a Bird meter or one of the retrofits, your accuracy will only be as good as the calibration of the slug, and then, only for a full  scale reading. Additionally, conventional wisdom is that the accuracy for used slugs, unless purchased from a reputable source, is essentially an unknown. If you calibrate your Bird slug using the MB-1 calibration feature, you can achieve 2% tracking with your measurement reference for nearly the entire scale (approximately the top 98%), even with a slug that is significantly out of calibration. Therefore, you can essentially make your MB-1/Bird element combination as accurate as your reference. This can be achieved because of MB-1's multipoint calibration feature. A description of how the MB-HF1 coupler can be used as a reference is given here.

 

Resolution is also significantly better. Take an element calibrated at 100w FS with MB-1. On a Bird meter movement, the scale gets compressed at the higher end. For example, you can probably only resolve the 98-100w segment on a Bird analog meter (the last two tic marks) to 1 part in 2 or maybe 1 part in 4. With MB-1, the same 98-100 watt range can be resolved to one part in 42.

Finally, your will be able to us all of MB-1's advanced features with your Bird line section.

 

Q: Can I use the Bird line section to drive MB-1, and then drive the Bird 43 analog meter with MB-1?

Yes. While the MB-1 display devices will give you more resolution, the Bird analog meter can be used as one of MB-1's external analog meters after being calibrated with the Panel Meter calibration feature. This makes sense, for example, if you want to locate an external meter at a different operating location than where your MB-1 is located. Of course, in this configuration, the Bird analog meter can be used in conjunction with any coupler, not just the Bird elements and line sections.

 

Q: Can I use a Bird slug with MB-1 for a different frequency range than for what it is specified?

I do not know if a big mismatch in the nominal  frequency range and operating frequency can cause any damage to the slug, so I will not comment on that aspect. With that caveat, measure the open circuit voltage at the frequency and full scale power you intend to use the slug at. If the DC voltage is at least 1 volt, it will work. Lower full scale voltages will work as well, but at decreased resolution.

 

 

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Analog Meters

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Q: How does the software control analog meter movements?

For linear movements, the level  required to drive a given meter movement  to full scale is determined during setup and then saved in EEProm. This data is used in conjunction with other user-defined information, such as the values of the full scale ranges, to map a measurement value from the coupler (or other input devices) to an analog meter reading.

For nonlinear analog meters, up to 50 different calibration points are supported (for up to two nonlinear scales per meter). Typically, as few as 20 points can do a good job, depending upon the meter scale. This mapping is also saved in EEProm, and used together with the user-defined ranges and full scale values to map a coupler measurement into an analog meter reading.

Cross needle meters have separate calibration tables for both directions of travel (50 points each for the forward and reflected directions) as do single needle nonlinear meters with two nonlinear scales, such as a power and SWR scale.

 

Q: What is "AutoRange Recovery Time?

When an analog meter is in the auto range mode, if the measurement value rises such that it exceeds the full scale value of the current range, the software immediately autoranges to an appropriate higher range. This ensures that the meter always provides an in-range reading. However,  when the signal decreases such that the new value is now in a lower range, the meter needs to "down-range" to maximize resolution and accuracy of the new value.  When this occurs, an AutoRange recovery timer starts, and keeps the range set to the higher range until this timer elapses.  This prevents the meter from rapidly hunting between two or more ranges for quickly varying signals such as CW and voice. You can think of this as somewhat analogous to the "fast attack" "slow decay" response on an S meter. MB-1 has an adjustable AutoRange Recovery Timer. Without the ability to customize this time interval to your preference, you may find that a single (compromise) value is too short or too long. You may also find that a single value may be suitable for some operating modes but not others.

Q: What is "Soft" Overrange?

Software controlled analog meters usually restrict the deflection of the pointer to the meter's full scale value to protect the meter movement.  While this protects the meter movement, unless the meter has some type of overrange indicator, you cannot distinguish a full scale reading from an overrange condition, including an extreme out-of-range condition. Not having some type of overrange indicator is not a good idea because while it may protect your meter movement, it may prevent you from recognizing an abnormally high power condition.

With MB-1, during analog meter calibration, the software allows you to define a soft overrange value, which is the maximum allowed meter deflection beyond the full scale reading that the needle will be allowed to traverse when an overrange condition is present. You can define a range between 0% to 100% beyond full scale deflection.  Typically an additional 5 - 10% needle deflection above full scale works fine to provide an easily identifiable overrange condition without risking any damage to the meter movement. MB1 provides an overrange LED indicator on the control head as well, but soft overrange is particularly useful if you locate an external analog meter away from the control head where the overrange LED may not be readily visible.

Q: On a Crossneedle meter, sometimes one needle is within range, and the other is above full scale. Is this normal?

Yes. Each needle on a crossneedle meter has its own soft overrange limits. What you are seeing simply means that one direction is within range, and the other direction is overrange (being limited by the soft overrange feature). When this condition occurs, If you have the AutoRange feature enabled, it will likely be the REFL needle that will be out of range since the AutoRange feature will keep the FWD needle within range. You will see this only under a high SWR condition.

To read a valid SWR on a crossneedle meter, both the FWD and REFL needles must be within range. Otherwise, the intersection of the two needles will not accurately represent the SWR.
 

Q: I have the analog meter set to AutoRange, but I sometimes see an overrange Reflected value. Shouldn't AutoRange kick in to the next higher range?

No. For a crossneedle meter, AutoRange is controlled solely by the value being read on the FWD power scale. The REFL power range must track the FWD range for the SWR values to be valid.   Unless you are running with a very high SWR, you will not encounter this problem.

Q: Why 12 power ranges for Analog Meters?  That seems excessive?

Many amateur analog power meters have three ranges (e.g., 20 watts, 200 watts, 2000 watts). Other common arrangements use a base of 10 (10, 100, 1000 watts), 3 (30, 300, 3000 watts), or 5 (50, 500, 5000 watts). If you want a meter that supports all of these popular ranges, you can do it with MB-1.

It should be pointed out that the 12 scale capacity applies to linear meter movement only. For single needle nonlinear meter scales,  MB-1 supports up to three power ranges and 1 SWR range. For Crossneedle meters, up to three power ranges are supported for each of the two directions (forward and reflected). 

 

Q: When in Auto range on the analog meter, how do I know what range I am in?

There are two methods: If the Panel Meter menu is being displayed on line 4 of the LCD, the current range is shown as part of the menu information.  Alternatively, since the 7-segment modules can display configuration information as well as measurements, one of the 7-segment display modules can be programmed to show the current full scale range of the analog panel meter.

Q: Where can I get additional analog meters?

There are typically several hundred analog meters available on eBay at any given time. Any DC meter with a full scale rating of 1 mA or less will work. For details on determining whether a particular Panel Meter can be used with MB-1, click here.
 

Q: Can I use a remote digital display analog panel meter in place of a conventional (needle) analog meter movement?

Yes. However, recognize that these panel meters are really just analog measurement devices with digital displays. Therefore, you will get some jitter on the reading. As long as you realize the limitation, feel free to experiment.  A more detailed description is given here.

Q: How far can I locate a panel meter from the base unit?

Use shielded cable, and you should be able to extend an external analog meter up to 150 feet from the Control Head. If you have a bad RFI problem, you will have to take measures to reduce the RFI, such as adding cable ferrites to the interconnecting cable.

Q: Will extending the distance between an external Panel Meter and the Control Head require recalibration?

For short runs, no. For long runs, maybe. The resistance of meter movements is usually low (a few hundred ohms), so adding a few ohms of cable resistance due to a long run can have some affect on the calibration. But a complete recalibration is not necessary. Use the DISPLAY function to exercise the Panel Meter's calibration verification test with the extra cable connected. If the meter still reads full scale at the highest calibration check point,  no adjustment is required. If the meter reads somewhat below the full scale deflection point at the highest calibration check point due to the added resistance, simply adjust the corresponding Panel Meter calibration pot on the left side of the case until the needle reads full scale. If the meter is a crossneedle meter, repeat this process for the REFL power needle as well. 

Q: Can I use MB-1 with components of an existing SWR or power meter?

Yes. You can use either the coupler components, the meter movement, or both from an existing power meter. Feed the coupler inputs from the existing meter into an MB-1 coupler port, and drive the meter movement in the existing meter from an MB-1 panel meter port. The coupler and meter movement in your existing equipment need to be disconnected from their internal meter circuitry, but you can use a multi-pole double throw switch to switch the leads from MB-1 back to their normal internal connections to allow the meter to operate stock.

 

Q: I calibrated an external Crossneedle meter correctly but the SWR readings are slightly inaccurate. 

Keep in mind that for crossneedle meters, MB-1 does not attempt to display an SWR value. After it calculates the FWD and REFL power levels, it simply drives the FWD and REFL needles respectively. Therefore, for crossneedle meters, MB-1 is relying solely on the meter face SWR curves to provide accurate SWR readings at the intersection of the FWD and REFL needles.

 

If the crossneedle meter was calibrated correctly, but the expected SWR readings are not displayed correctly at the intersection of the Forward and Reflected needles,  then the meter face on the external meter you are using has a calibration error in the SWR curves. MeterBuilder has confirmed this problem on a few of the popular crossneedle meters.  Usually the errors are small, and would not be easily recognized without the types of utilities that MB-1 provides to confirm calibration.
 

The source of the problem is easily confirmed by running the MB-1's Demo mode simulator at a constant SWR (use any virtual power coupler, except virtual coupler 7 which applies up to one SWR unit of variability). Set the Demo mode for the ST2 mode (step mode 2), which will hold each simulated sample for approximately 5 seconds. Jot down the forward and reflected power values for one of the snapshots.  Plug these numbers in to the online SWR calculator, or use some other independent SWR calculation. If the independent SWR calculation matches the expected SWR value that the simulator is running at, you have confirmed that MB-1 is driving the forward and reflected needles to the correct power points, and therefore, there is a calibration error in the SWR curves on the meter face you are using.

You can also confirm this problem independent of MB-1. Simply apply a DC voltage through resistors to the forward and reflected connections on the crossneedle meter under test to position the needles statically (you can use the variable 0 -5 volt source on the rear panel of MB-1 to aid in this test). Again, use the online SWR calculator or another independent SWR calculation to determine if the forward and reflected power values are consistent with the SWR value indicated at the intersection of the two needles.

Q: Are there any special restrictions when using MB-1 with a high accuracy "taut band" analog meter or with a Professional Grade analog meter?

No - as long as its full scale drive requirements are 1 mA or less. (For those not familiar "taut band" meters, these types of meter movements are found in high end equipment, such as the type of analog meters used in some of the Bird Wattmeters. The armature of the meter movement is suspended by fine wire, essentially reducing the needle friction to nearly 0, which results in extremely repeatable readings.)

Q: What are the rules that determine whether I have to calibrate an external Panel Meter as Linear or Nonlinear?

If your meter face has at least one nonlinear scale, you must calibrate the Panel Meter as a nonlinear meter, even if it the meter face also has one or more linear scales on it. In this case, you will simply treat the linear scales as a special case of a nonlinear scale. To simplify setup, when asked to specify the number of points you wish to calibrate the linear scale with, specify 1. 

 

Q: I have a nice large analog meter with a single linear scale that reads 0 - 10. But since the scale starts at 0, how can I display both power and SWR on this single scale?

Assume that you have a linear scale that ranges from 0 - 10. When calibrating this meter with the MB-1 setup routines, specify the meter scale as "Linear". Set up the Power scales as desired (for example three power scales at 10, 100, and 1000 watts). During the SWR portion of the setup, you will be asked to specify the starting value of the SWR scale as 0 or 1. Since the meter has only a single scale that starts at 0, specify 0. Set the SWR range (full scale SWR value) to 10. The software will use this information to set the resting position of the needle to 1 when the meter is displaying SWR. With this approach, in addition to your three power scales of 10, 100, and 100 watts, you will also have an SWR scale with a range of 1 - 10.

 

Admittedly, an analog SWR meter with a scale that starts at 0 is unconventional, but without this feature, any 0-based analog meter would be ruled out for use with SWR measurements.

Q: Can I mix and match Couplers and Panel Meters?

Yes. Any coupler can be used with any of the five (max) panel meters that can be connected to MB-1.  And the same applies in the opposite direction (all four couplers (max) can be used with panel meters that have compatible ranges).

Take a simple example. Assume that you have a single coupler connected to the output of your amplifier, which feeds a single antenna.  Assume further that you have two transceivers at different locations in your shack, both feeding the amplifier through a coax switch. With this configuration, you could locate the MB-1 meter near transceiver 1, and use the internal crossneedle meter when using that station. You could also connect another crossneedle meter, or conventional (single needle) meter to MB-1, and locate that meter near the second transceiver. This gives you remote display capability.

To simplify switching between stations, you could configure the settings for station 1 into one of MB-1's  configuration sets, and the settings for station 2 into a second configuration set. Simply select the appropriate configuration set, and MB-1 will change its configuration to drive the appropriate panel meter using the same coupler. In this simple example, both configuration settings would be identical, with the exception of the panel meter. But you could also change any or all of the other meter parameters to suit your needs and save them in a configuration set. For example, one configuration set could be set up to display Peak Power at the transceiver 2 panel meter and the other configuration set could be set up to display average power at the transceiver 1 panel meter.

Q: What is the big deal about a linear scale crossneedle meter?

Other crossneedle meter scales are nonlinear to account for the nonlinearity of diode detectors and other nonlinear aspects of the coupler used with the meter, most notably the square law relationship between coupler output voltage and power. This results in a highly compressed scale at the high end of each range resulting in poor resolution.  A crossneedle meter with linear scales does not have that problem.

Another problem with some nonlinear crossneedle scales is the occasional need for multiple scales, even for x10 scales, since the degree of the nonlinearity differs between the x1, x10, and x100 scales. This further complicates the reading of such scales.

 

Q: Can the included crossneedle analog meter be used for RF Ammeter and Generic Meter Applications?

Yes. When an RF Ammeter coupler of Generic Meter application is selected (vs. an RF power coupler), and a crossneedle analog panel meter is selected, the software automatically disables the reflected needle on the crossneedle meter (which has no meaning for non-power applications). All other analog meter functions are available, including AutoRange and overrange detection (including soft overrange). The following measurement modes are available for display on the analog meter for non-power applications: TUNE (instantaneous value), PEAK, AVERAGE, MIN/MAX captures of these measurement types.

 

Q: I want to use an analog scale that does not start at 0 for a Generic Application. Can MB-1 calibrate  a scale like this?

Yes. As an example, see this Generic Meter Application that has an analog meter with a temperature scale that ranges from 70 degrees Fahrenheit to 170 degrees Fahrenheit. Although this scale is used with a Generic Meter Application, the same approach can be used to get a similar "expanded scale"  for power and RF ammeter applications as well.

For the temperature example, during setup, specify the meter type as Nonlinear.  (Even though the meter movement and scale in this example are linear, this must be done because the scale does not start at 0.)

Set the Full Scale value to 170. Set the number of lineup points to 17. This will give you calibration points at 10, 20, 30, ... 150, 160, 170.

All calibrations points must be set, even though we are not interested in those values below 70. Therefore, we do need to calibrate the "don't care points" below 70 degrees. To do this, offset the mechanical zero bias of the meter so that it reads off scale below the smallest value (CCW of 70).  For calibration points of 10, 20, .. 60, advance the front panel pot slightly starting from the most CCW position of the pot, keeping the needle below the first valid point on the scale (70). Do this for all remaining "phantom points".  You must advance the needle forward slightly after calibrating each of these phantom points since the software integrity checks require the ADC value to be monotonically increasing for all of the calibration points (including the "don't care" points).

Once you reach the calibration points for 70 degrees and above, calibrate the meter in the normal fashion, simply dialing the needle to each calibration point, pressing the SELECT menu button to save each calibration point.  In this example, after calibration, any value from 70 - 170 will read correctly. Any value less than 70 will read off scale below 0 (which provides a somewhat useful under range indicator).

 

Q: Can MB-1 be use to validate (or generate) the SWR curves on Crossneedle Meters?

Yes. When driving a crossneedle meter, MB-1 displays the FWD an RF power without regard to the SWR value. If the FWD and REFL power scales are calibrated properly, the intersection of the FWD and REFL needles should read the correct SWR value.  Since the simulator has a programmable SWR range of 1.1 to 9.9 in steps of .1, you should be able to drive any crossneedle meter (FS of 1 mA or less) across its full set of SWR curves. After programming an SWR of interest (Demo mode menu Setup), the best way to do this is to set the simulator to the SWEEP mode, which causes the FWD needle to repeatedly sweep from 0 to its full scale value, with the REFL needle tracking based on the programmed SWR values. If an SWR curve under test is correct, the intersection of the swept needles should exactly trace out the SWR curve.

 

SWR curves can also be created with MB-1. The following discusses two different approaches using MB-1:

 

1.  Using the Simulator -  In this case, use the STEP1 mode of the simulator, which selects a random FWD value, upper bounded by the full scale vale of the associated coupler (and the corresponding REFL power based on SWR), and holds the reading for about 5 seconds before selecting the next random power level. Apply a mark on the scale at the intersection of the needles for a number of points until you have a range of points extending from low power levels to high power levels.

 

2. Using a Real Coupler Port - Select a real coupler port (1 - 4) whose Full Scale value is the same (or a multiple .(01, .1, 10, 100, etc) of the Full Scale FWD power of the crossneedle meter. Drive the FWD and REFL ports of the selected coupler with two potentiometers. (You can use the front panel pot port on the rear panel RCA jacks for one of these.) This will allow you to arbitrarily dial in any FWD and REFL power levels. If you dial in a series of FWD, REFL power levels pairs corresponding to a particular SWR value, the intersection of the needles will define the locus of points for that (single) SWR curve. You can mark the scale with an arbitrary number of points. Usually, eight points are adequate for each SWR curve, but if the meter face is very large, you may need more. (You will also notice that some of the SWR curves have more curvature than others and these may require a larger number of points.)
 

Q: When operating SSB, I don't get as much bounce in the needle as I expect to.

If you have the Analog Meter AutoRange feature enabled, the meter will typically operate in the range determined by your peak power. For example, if you are using the internal crossneedle meter on MB-1, which has three forward full scale ranges (20 watts, 200 watts, 2000 watts), and if you are using a 100 watt transceiver, since your peak power will usually exceed 20 watts, the meter will typically be in the 200 watt range for most of your transmissions. (The AutoRange feature up-ranges to the lowest in-range scale, and stays in that range for an interval determined by the AutoRange Recovery Time.) When you also take into account the inertia of the meter needle, and the fact that SSB average power may be 20% or less of your peak power, the needle will typically spend most of its time in the lower end of the scale in the above example.

If you want larger deflection, simply turn the AutoRange function off, and pick a lower value manual range. (The Soft Overrange feature will protect the meter movement). In the example above, if you were to choose the 20 watt manual scale, the needle will show a much larger deflection with a 100 watt SSB signal. Of course, in this case, you are using the needle indication as a relative indicator only, but this technique is useful for giving you more resolution (deflection), and with some experience, you will see what your "normal" signal looks like on that scale. If your signal then changes for some reason, or if you want to see the impact of modifying your transmit audio level on your signal, you will be able to see changes more easily with the analog meter set to a lower power manual range.

 

 

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Seven Segment Displays

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Q: How do I modify the 7-segment displays if I want to change the colors of all or some of the 7-Segment Displays?

The LEDs are plugged into 40 pin sockets, and are easily replaced.

Q: I  want to display just three parameters on the internal 7-Segment Displays. Can I turn the fourth module off?

Any or all of the internal 7-segment LEDs as well as the external 7-segment LED modules can be turned off completely by setting the Display Mode to "OFF" using the 7-Segment Display menu.