Juma PA-100D v1.06a

Software developed by Adrian

Juma PA-100D v1.06a

Postby 5B4AIY » 24 Nov 2014 14:29

I had not intended adding any further features or modifications to the Juma PA-100D amplifier, but a recent Field Day problem prompted me to re-think this decision. The problem could have quite easily been solved had there been some simple test equipment available. In an effort to preclude this from recurring, I decided to add a couple of features to the PA-100D to further enhance its utility.

Frequency Display
When using the amplifier in the F-SENSE mode of auto-band detection, the input frequency is counted, and this is now displayed. Whenever this mode is selected, an additional display page is available that will show the current RF input frequency in MHz to a resolution of 1kHz. The current forward power is also displayed on this page. Note that this additional page is only visible if the F-SENSE mode is selected. The input sensitivity for both automatic band detection and frequency display is such that reliable displays can be obtained with input powers as low as 100mW, corresponding to 2.24V RMS, 6.3V P-P, into 50 Ohms up to at least the 6m band. (The sensitivity is slightly reduced on 6m.)

Obviously the amplifier will not operate on 6m, but the frequency counter, power meter, and SWR meter are functional.

The accuracy is such that when properly calibrated the display is accurate to +/- 1kHz which is sufficient for normal amateur frequency confirmation. An additional word of EEPROM memory is used to store the frequency meter calibration constant, and thus this version of the firmware will cause a Checksum Error on initial start-up. Save your current calibration and configuration data before loading.

To calibrate the frequency meter, step to the frequency meter calibration page in the Service Menu, and inject a CW carrier accurate to at least +/-100Hz, and set to an integer kHz value on the 10m band. The default rapid bandswitch 10m frequency of 28.850MHz of the Juma TRX-2 is ideal. With the amplifier connected to a dummy load, key the transceiver and note the display. Using the UP/DOWN buttons adjust the display to agree. I suggest then stepping until the display just changes to 28.849 then count the number of steps in the reverse direction until it changes to 28.851 and then count back half the number to set the calibration in the centre of its range.

Note that this simple frequency counter is really an Events Per Unit Time (EPUT) meter. In order for it to be interpreted as frequency two conditions have to be met:

a: The input signal must be continuous;

b: The events being counted must be uniformly distributed throughout the gate time interval.

In practice, this means that the input signal must be an unmodulated continuous carrier. Note that some transceivers offset their carrier when transmitting CW. If either the Juma TRX-2 or the Elecraft KX-3 is used, then the CW carrier frequency is as displayed. In the case of the Juma TRX-2, use the TUNE mode; use either an unmodulated AM or FM carrier for the KX-3.

Power Meter Display Type
The output power meter can now be set to display powers either in Watts or dBm. This latter unit facilitates easy measurement of gains and losses. In the case of a recent Field Day exercise the loss of a suspicious cable could have easily been measured. Simply set the transceiver and the amplifier's gain controls to achieve a CW output power of about 40W - 60W, +46dBm - +47.8dBm. Then replace the transceiver to amplifier link with the suspicious cable, and key the transceiver again. The difference in dB of the output power represents the insertion loss of the cable.

Power Meter Accuracy
Most of you will have already noticed that in the STANDBY mode the power displayed on the output meter is significantly lower than that displayed on the Juma TRX-2 output meter. This version of the firmware addresses this, and the accuracy at low powers has been improved. As a result, an additional calibration page is present in the Service Menu, as well as an additional word of EEPROM memory used. This will cause a Checksum Error on initial load. Make a note of your existing calibration settings prior to loading this firmware.

To calibrate the amplifier's power meter, connect the amplifier to a good dummy load and a known accurate RF power meter. From the power-off state select the Service Menu, select the high power page, and key the driving transceiver to give an output of about 60W - 80W. When the display has stabilised, adjust using the UP and DOWN buttons so that the power meter agrees with the external instrument. Then select the next page, and again key the transceiver. This time the amplifier will remain in the STANDBY mode and only the driver transceiver's output power will be displayed. Again using the UP/DOWN buttons adjust the display to match the external power meter. Briefly press the PWR button to return to the high power page, and re-adjust if necessary. By swapping between the high and low power pages it should be possible to obtain a reasonably accurate display over the complete range. Note that the power meter is deliberately suppressed for output powers of less than about 400mW. Briefly press the OPER button, respond to the prompt to save the new settings, and exit.

Power Meter Display
Previously the power meter would only display if the amplifier was keyed, even in the STANDBY mode. This is no longer necessary. The power meter will display forward power even in the STANDBY mode without the necessity of actually keying the amplifier. The meter display is cut-off however for powers less than 400mW/+26dBm as the accuracy degrades considerably at such low powers. In addition, the SWR display is also active in STANDBY, allowing you to match your antenna system without using high power. Note that because of the reduced sensitivity at low forward powers the measurement will be less accurate, but still sufficient for an initial match to be made.

Page Increment/Decrement
In the previous firmware it was only possible to increment the Service and Configuration modes display pages. This has now been improved. As before, a brief press of the DISPLAY/CONFIG button will single step forward. If the button is held, the pages will automatically increment.

To step in the reverse direction, briefly press the PWR button. If the button is held, the pages will automatically step backward. In either case, whenever page zero is displayed there will be a long beep and a longer page switch delay.

Obviously using the PWR button in this way means that you must exit from either menu in order for the normal power off function to be available.

In the previous version if the A-D convertor display was invoked in the Serial Test Suite, at the conclusion of the test the band would be set to UNKNOWN and the message 'Err' displayed. This has been fixed. The amplifier's band selection is unaffected by the use of the A-D convertor test.

When displaying a static continuous output power, the display would blink whenever the display update occurred. This inadequate update suppression artefact has now been fixed. The display update is now invisible.

With these additional features the utility of this amplifier has been enhanced so that it can now offer some simple test equipment that should prove useful when operating in the field.

As mentioned, the EEPROM mapping has been changed! Loading this version WILL CAUSE a Checksum Error on initial start-up! Make sure you have made a record of your calibration and configuration settings BEFORE loading this new firmware! Then re-enter your data, and redo the power meter calibration, as well as the initial frequency meter calibration. If you are updating from an original version, then as the measurement system is completely different, you will have to re-calibrate your amplifier. Fortunately since the bias currents are hardware settings only the software calibration factors will need re-settings.

73, Adrian, 5B4AIY
PA-100D v1.06a Build 4 (C-Source+HEX Load File+User Manual).zip
Power meter accuracy improved, powers displayable in W or dBm, Frequency Meter added, SWR accuracy improved.
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