Interfacing your own Couplers to MB-1

In the figure below, we are feeding the output of a Yaesu Mark V (200 watts max output) through both the coupler being calibrated and the Alpha 4510, which we are using as the reference meter in this example. The output terminates in a 50 ohm resistive dummy load.

Below we provide a complete step by step example of the coupler calibration procedure. We calibrate the coupler in this example for a full scale reading of 1000 watts. The coupler being calibrated happens to be the MB-HF1 coupler - the coupler included with the MB-1 meter, but the same procedure applies to any Bruene type coupler.

During the calibration procedure, you are asked, via prompts from the LCD screen, to identify the band that you are performing the calibration at. This is referred to as the Reference Band. This information is used by the band compensation routines as explained in the User's Manual.

Typically, you will need to perform the calibration at only a few power levels based on how closely the coupler being calibrated follows the power/voltage square law relationship, but 48 different power levels are available in the 0 - 2000 watt range. With careful calibration, this will allow you to calibrate a coupler that will track the reference it was calibrated with to within 2% across the full power range provided that the coupler has adequate sensitivity  (see the "Evaluating Couplers" page).

If, after the initial calibration, you find an operating power range where the accuracy could use some improvement, you do not need to repeat the entire calibration. You can use the Coupler EDIT function to add a calibration point or two in the range where the accuracy needs improvement (or you can redo the calibration of an inaccurate calibration point if required).


Coupler Calibration Setup

(Darker Bezel shipped with kit.)


Complete Coupler Calibration Example

Forward Channel Calibration

As with all Set-Up functions, first display the applicable menu on line 4 of the LCD (Coupler Menu). Then press the Set-Up button (Top Right Button - Long press).


Select Coupler:

The software will enter the coupler calibration setup routine bringing up the screen to the right. Press the UP or DOWN buttons (M1 or M2) to select the Coupler you want to calibrate. (In this example, coupler 4 has been selected) Then press SELECT (M3).

Make sure you use the UP/DOWN "buttons" represented by the first two menus choices on the top line of the LCD using the MENU-1 and MENU-2 buttons, and not the buttons with the Up-Scroll and Down-Scroll silkscreen labeling.



Erase Settings?

If the Coupler that you selected was previously calibrated, you are given the option to erase the previous settings or to EDIT the current settings.

If you want to perform a new calibration as we do here, press YES (M1) to erase the old settings. If, instead, you wanted to EDIT the settings of a previous calibration, you would press NO (M2)

Since we are doing a new calibration, we do not use the EDIT function in this example, but the EDIT prompt (had you chosen NO) is displayed at the end of this table for completeness.



Select Calibration Type:

This screen specifies the type of calibration to be performed on the selected coupler port. The choices are PWR (RF Power Coupler), AMPS (RF Ammeter coupler), or GENER (when using MB-1 with Analog Sensors). Since we are calibrating a power coupler, select PWR (M1).



Adjust FWD Coupler Trim Pot:

The screens on the right aid in adjusting the coupler's FWD port trim pot for maximum sensitivity without overdriving the Amp/Mux in MB-1.

Typically, to adjust the FWD port trim pot, you set the transmit power to the full scale value you want to calibrate the coupler at (which would be 1000 watts in this example), and then adjust the FWD trim pot until the FWD ADC reading on the LCD reads approximately 30,000 - a value slightly below the max Amp/Mux 15 bit value of 32,736 to guarantee some margin.

However, since we do not have a transmitter capable of outputting 1000 watts in our sample setup, we consult the User's Manual to determine  the value that should be used to adjust the trim pot to when using a power level below the FS value to adjust the coupler trim pot (This will likely be a typical case for many users.)

If you follow the formula in the User's Manual, when the desired FS value of the coupler is 1000 watts, and the power being applied to adjust the trim pot is 150 watts (a reasonable value for the Mark V), the FWD trim pot should be adjusted to an ADC value of approximately 11,600. This is an approximate setting. It is important that you be in the "ballpark" only for this step. It is better to err on the side of setting this value to a slightly lower value since the goal of this step is to prevent overdriving MB-1's input circuitry.

When the top screen in the right column is displayed, press any menu button (M1 - M4) to display the actual FWD and REFL ADC values being applied to the coupler FWD and REFL ports. This is shown in the second screen. This screen shows the ADC values (0) with no power applied.

The photo at the far right shows the screen when power is applied and the FWD trim pot is properly adjusted.

After adjusting the trim pot, remove transmit power. Then press any menu button to continue.



Click to Expand


OEM Option:

The User's Manual explains the details of the preloaded OEM tables. The MB-HF1 has its calibration table preloaded in EEProm. If you are using this coupler (or other couplers that may be supported by this feature in the future), the entire calibration table, including any band compensation calibration values, can be loaded into the coupler port you are calibrating simply by answering YES to this prompt, and then entering the OEM numeric code for the corresponding coupler. This eliminates the need to perform the point by point calibration steps listed below. (However, you still need to adjust the FWD and REFL trim pots as per the manual.)

Even though we could have used the OEM option for the MB-HF1 coupler in this example, we will answer NO to this prompt so that we can demonstrate the step-by step procedures below for performing a custom coupler calibration.

Select Reference Band:

Use this screen to specify the Reference Band. This is the band you will use when performing the FWD power calibration. If your transceiver supports 80 meters, this is a good band to use.

The "Reference Band" holds the main calibration data, and is also used by the  band correction algorithms, since the correction table measurements for each band are made with respect to the calibration point measurements performed in the Reference Band.

Specify Full Scale Power:

This screen is used to specify the FS value you intend to use with this coupler. This information is used to determine the list of calibration points you will be offered during the  calibration procedure. (When we set the FS value to 1000 watts as shown to the right, no calibration points greater than 1000 watts will be offered for calibration during the actual calibration sequence.)

This FS value is also used to set the Full scale value that the Simulator will generate when the Simulator is used to generate simulated values for this coupler.

Actual Calibration:
(Calibration shown at .1w Calibration point)

The software then displays a screen similar to the one on the right for each calibration point, starting at .05 watts, and ending at the calibration point closest to the Full Scale power you specified above.

To calibrate each point, apply the nominal power as displayed on the LCD, using a transmitter and reference meter. Then press SAV (M1). The screens to the right show the prompt and the reference meter reading for the .1 watt calibration point.

Remember, you do not need to calibrate all of the calibration points within the FS range that you specified, but you must perform a calibration at least one power level for the software to consider the calibration valid.

To skip a calibration point and move to the next higher power  calibration point, simply press NXT (M2).

After each point is saved, the screen automatically advances to the next available calibration point. Use the PREV (M3) button if you need to go back to lower power calibration point for any reason. Use the DEL (M3 - short press) button to delete a calibration point (useful if you know that a calibration point has a significant error, and you do not want to recalibrate that point).

Note: You will achieve better accuracy by calibrating with a smaller number of accurate calibration points rather than with a larger number of poor quality calibration points.


Click to Expand

End Calibration after last calibration point:

A photo of the final calibration point (150 watts) is shown in the far right column. (We are ending here since we do not have a 1 Kw power source in this example.)

When you have saved the calibration data for all of the desired power points, terminate the current calibration session by pressing END (Long press to M4). This will allow you to save the calibration points below.

Convention: All menu choices that perform a single function (like SAV, NXT and PREV in the menu to the right) are requested with a short push of the corresponding menu button.
Since there are only four menu buttons (M1 - M4), those menus that have five choices like the one shown to the right on line 1 of the LCD are handled as follows. For this menu, the Last menu item DEL/END controls both the DELete function and the END calibration function. For these dual menu cases, you select the first function (DEL) with a short press of the corresponding menu button (M4 in this case). You select the second function (END) with a long press of the corresponding menu button (M4). 




Click to Expand

Perform Frequency Correction:

After ending the reference calibration, the screen to the right presents you with the option to perform Band Calibration. Until you are comfortable with the basic (Reference Band) calibration described here, it is suggested that you skip this step by pressing NO (M2). You can EDIT this coupler table at a later time to add the band compensation points. (Your coupler will still be useable on all bands, but will make use of the single Reference Band calibration data in this case.)

Full details for performing Band calibration are given in the User's Manual.

Save Prompt:

The screen at the right is the SAVE prompt. To save the calibration data to EEProm, press SAVE (M1).

To abort without saving the current calibration data, press EXIT (M4).


The screen to the right confirms that the calibration data was saved to EEProm.


The software now gives you the option to EXIT (resuming normal meter operation) or to TEST the coupler. The TEST option displays the ADC values corresponding to the DC voltages on the FWD and REFL ports of the coupler.  Think of this as a simple continuity check to verify that the coupler you think is connected to this coupler port is actually connected properly, and that the magnitude of the displayed ADC values increase or decreases as power applied through the coupler increases or decreases.

In the example above, we performed a new calibration. Had we chosen the EDIT option to edit the existing calibration table (by answering NO to the ERASE request at the beginning of the example), the screen to the right would have been displayed.

To EDIT the existing FWD power calibration table (the Reference Band), press FWD (M1). This will bring you to the actual calibration sequence described earlier in the above example. Once in this mode, you can select one or more previously calibrated points and recalibrate them,  or you can select power points that were not previously calibrated, and include them in the coupler's calibration table.

To perform (or edit) band calibration, enter FREQ (M2). Band calibration is covered in detail in the User's manual.


Adjust the Reflected Channel Trim Pot

The calibration steps above performed the calibration on the FWD port. The only operation required for the REFL Channel is adjustment of the REFL channel trim pot. The instructions are given below.

Make sure the transmitter is off. Reverse the FWD and REFL coax connections on the coupler so that the transmitter is feeding the LOAD side of the coupler and the dummy load is connected to the TX side of the coupler as shown at the right.


Apply Reference Power:

Apply a reasonable power, for example 50 watts, as measured by the reference meter (the coax connections on the reference meter should not be left in the normal configuration).





Place MB-1 into the Reflected Channel Calibration Mode:

Activate the RefCal (Reflected Channel Calibration) mode with a long press to M2. This places the meter in a special mode that is used solely to adjust the REFL coupler trim pot.

You will see the confirmation screen on the right (top line) indicating that the software has entered the Reflected Channel Calibration mode. The yellow LED on switch RefCal switch M2 will also flash repeatedly  to remind you that you are in this special calibration mode.

Adjust Reflected Channel Trim pot:

Adjust the REFL port trim pot until the reflected channel reading on the MB-1 display matches the reference power meter's reading.

Ignore any other readings on the MB-1 displays, such as the FWD or SWR reading when in this mode.



Click to Expand

Exit the Reflected Channel Calibration Mode:

When done adjusting the REFL channel trim pot, press the RefCal (M2) button (any duration).  A message will be displayed indicating that the software is exiting the Reflected Channel Calibration mode as shown on the screen to the right (line 1). The meter is now in its normal operating mode.

Turn the transmitter off.



Display the Coupler Calibration Data on the LCD

You can display the internal calibration table data for the coupler you have just calibrated. This information can be displayed at any time (not just following calibration) using the meter's DISPLAY function.
Coupler Menu:

As with all DISPLAY functions, first display the applicable menu  (Coupler Menu in this case) on line 4 of the LCD. Then select the coupler you want to display the calibration data for (coupler 4 in this example). Then press the DISP button (Top Right Button - Short press).


View Display Data

Page 1:

The display function starts and the first page of the Coupler calibration data is displayed on the LCD .

This data identifies the coupler number, the FS power, the number of calibration points you saved during the calibration sequence, and the FWD trim correction factor (not discussed here - see User's manual). 

Since this display has multiple pages, press the DISP button (short press). Each press advances to the next page of information.

Page 2:

The second screen displays the Reference Band that the coupler was calibrated at.



Page 3:

The screen to the right (and subsequent screens, depending upon the number of calibration points you performed the calibration at) displays the data for each calibration point, namely the nominal power level and the corresponding ADC value. This example assumes that seven power points were calibrated.



Page 4:

The last 3 calibration points are displayed on the screen to the right.



Page 5:

If band correction had been performed, this information would be displayed here.

The OEM table associated with the MB-HF1 coupler contains band correction data that you can view if you wish to see what this data looks like. Coupler 1 (factory default) is loaded with the calibration table for the MB-HF1 coupler (OEM coupler 1).



TEST or EXIT Prompt:

After the calibration data is displayed, the software gives you the option to EXIT (resuming normal meter operation) or to initiate a coupler TEST. This TEST function was described earlier in this example.

Display Function Exits:

The meter now resumes normal operation.





Verify the Calibration

You will probably want to do a sanity check at a few points using your transmitter with the reference meter still inserted for comparison. After calibration, check power at a few points covering the low, medium, and high power ranges. If accuracy needs improvement in a certain power range, you can EDIT the coupler to add one or more points in that power range (or you can correct an inaccurate calibration point in that power range).

With the above calibration, the accuracy was found to be very good across most of the power range, but measurements around 100 watts, while reasonable, did not quite match the accuracy of other power levels. Adding a calibration point at 100 watts resulted in good accuracy across the full power range (worst case was within 2% of the reference, typical was within 1% of reference).


Examples - Using MB-1 with Other Couplers