Juma TRX-2 Firmware v1.20c

Software developed by Adrian

Juma TRX-2 Firmware v1.20c

Postby 5B4AIY » 24 May 2015 10:47

This version of the firmware, 1.20c Build 3 modifies the way the Rapid Band Switch feature operates, as well as the way the output power and power meter calibration is performed.

Please read the section of the User Manual dealing with the RF Power Meter calibration - the maximum power setting during calibration is now 5W. The previous setting of 10W subjected the output transistors to the possibility of excessive dissipation as well as an accidental over-drive blowing fuses. If you set the output power to 10W in the Calibration & Setup mode with this firmware you will almost certainly blow fuses when using the transceiver as the output power will now be far too high - YOU HAVE BEEN WARNED! Remember - the setting is now 5W.

Rapid Band Switch
Several firmware revisions ago I introduced the Rapid Band Switch (RBS) feature to allow the quick selection of an amateur band. In the previous versions there were three modes of operation:

a. Default - the frequencies were preset in the EEPROM and could not be altered, but were 'legal' in all three regions for which the transceiver could be configured;
b. User - the frequencies were initially the same as those for the Default mode, but could now be changed by the user with a single button push;
c. Locked - the frequencies were the User Mode settings, but which were now read-only to prevent an accidental change.

Most commercial transceivers also have a quick method of selecting an amateur band, but when the band is changed the current frequency and mode is saved, so that when returning to the original amateur band the previous frequency and mode is restored.

This version of the firmware now offers this option in addition to the previous options, set on page 22 of the User Configuration menu. There are now four modes:

a. Default - as before, preset EEPROM frequencies;
b. User-A - the same as the previous User mode, the frequency can be changed with a single button push;
c. User-B - the new mode whereby when leaving an amateur band the current frequency and mode is automatically saved to the User Band memory;
d. Locked - the User Mode settings are locked to prevent an accidental change.

Note that the frequency is saved to the User Memory in RAM - if you wish these changes to be preserved, then you have to either deliberately save the current settings, or else choose a suitable Power Off mode, so that they are saved to the EEPROM.

You can always save the current state of the transceiver by pressing and holding the DISPLAY/CONFIG button to enter the User Configuration mode, and then release the button, and then press and hold it a second time, and, responding to the prompt, briefly press the MODE button to save the current settings.

The Power Off mode has three options, and is set on Page 27 of the User Configuration menu:

a. Immediate - the transceiver will immediately power down;
b. Prompted - when powering off, you will receive a prompt asking whether you wish to save the current settings;
c. Save State - the current state of the transceiver is always saved prior to dropping the power latch.

In the Immediate mode, if the Changed flag is set, then this signifies that there has been a change to one or more band switch memory or VFO memory settings, and thus an automatic save will occur prior to shutdown. If no changes have been made, then the power down is immediate.

The manufacturer of the microprocessor guarantees that the flash EEPROM memory is good for about 100,000 write operations, consequently even if you select the Save State option and use the transceiver 5 times a day every day of the year it would take more than 50 years to exceed the maximum write capability and run into errors.

RF Power Output & Calibration
In all previous firmware revisions the RF Power meter was calibrated at the maximum power of 10W. This involved setting the CARR control on the main board to give an output of 10W as measured on an external RF power meter, and then adjusting the calibration constant so that the internal power meter agreed. Whilst this can be safely accomplished if you are careful, it does subject the PA to significant thermal stress, and, if an accidental over-drive occurs, you can easily blow the main fuse. The transceiver is not really rated for continuous operation at 10W, and therefore I elected in this firmware to reduce the thermal stress by calibrating and setting the power output using the maximum attenuation setting of 3dB rather than the previous setting of 0dB.

In this firmware, connect the transceiver to a suitable 50 ohm dummy load and an RF power meter. Select the Calibration & Setup mode, step to the RF Power meter calibration page, (Page 4), and when this page is selected the TUNE mode is engaged, and the attenuator is now set to 3dB. Press and hold the PTT switch and adjust the CARR control for 5W on the external meter, and adjust the calibration factor with the VFO knob so that the internal power meter agrees, then release the PTT switch. Save and exit from the calibration mode to preserve these settings. You should now find that in the TUNE mode with 0dB as the tune mode attenuation that the output power is 10W. The TUNE mode attenuation can be set in 1dB steps from 0dB to 3dB on Page 24 of the User Configuration menu.

The resistor values chosen for the attenuator give reasonably accurate attenuation settings. If they are exactly at their nominal values, then the -1dB attenuator is actually -0.936dB, the -2dB attenuator is actually -1.960dB, and the -3dB attenuator is actually -2.982dB.

It was certainly noticeable when adjusting the power output and calibration settings in the previous firmware that the PA temperature would quite rapidly rise, and as this reduces the gain and power output you would find that although you had set the output to 10W, after the PA had cooled down when checking at the -3dB setting the power would now be 6.5W - 7.2W as a result of the temperature change, which would require you to reset the CARR control to avoid excessive output. With this new method, whereby the power is set at the 5W level with the 3dB attenuator in circuit, you will find that this re-adjustment should not be necessary.

Note that the output power is both temperature and voltage dependant. Setting the output to 10W at an ambient of 33C caused it to be 12W at a 20C ambient. Setting it to 10W at 13.8V results in about 8W at 12V, so do not be surprised if your output power appears to vary somewhat. As you can see, it is still possible to 'tweak' and provide little enhancements to this firmware to further improve this lovely little transceiver.

If you mainly use this transceiver to drive the companion PA-100D linear amplifier, you might also give consideration to setting the maximum output with the 0dB attenuator to 5W rather than 10W, as this is more than sufficient drive for the linear to achieve maximum output.

As there are no EEPROM changes, this version can be safely loaded over a previous 1.11 or later version. As always, it is a wise precaution to make a note of your existing calibration and configuration settings prior to loading this version, and there are pages at the end of the User Manual specifically for this data.

If you are updating from an earlier version, then there will be a checksum error on initial boot, and the standard defaults will be loaded. This is normal and only occurs the first time. Make a note of your calibration and configuration settings, and re-enter them. There will be an additional entry for the choice of RF power meter display, dBm or Watts.

If you are updating from an original version of the firmware, then you will have to re-calibrate as the measurement system is completely different. Please read carefully the section in the User Manual that describes this.

73, Adrian, 5B4AIY
Juma TRX-2 v1.20c Build 3 (C-Source+HEX Load File+User Manual).zip
Added Rapid Band Switch option, modified the RF Output/Power Meter calibration.
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