I’ve added a more user friendly power display and control system to the OpenGD77 firmware
Initially the only way to control the Tx power was to set the raw PA drive level number in the Options screen.
Although this was OK for the developers and testers, its was never intended to be the final solution, so today I have implemented a new feature which makes the power control more user friendly.
The power can be set to 250mW, 500mW, 750mW, 1W, 2W, 3W, 4W or 5W.
The power is displayed in the middle of the top of the display.
To change power level.
Press Function + Right to increase power
Press Function + Left to decrease power
The output power will only be accurate if you calibrate your own radio, because the factory calibration for Tx power hardly ever seems to be accurate.
I checked one of my GD-77’s today and the “Low” power calibration point which is supposed to produce 1W was only producing 0.35W on UHF, and the “High” power calibration point was only producing 3.5W
This is despite the battery being fully charged.
I used the calibration editor in the Community CPS to enter new values for the Low (1W) and High (5W) calibration points, and after I did that, the power output was correct to plus or minus 0.1W according to my power meter.
For those interested in the technical details…
The calibration data stores the Tx Power calibration points for multiple 5Mhz wide frequency bands, for both the High and Low power settings available in the official firmware.
The value stored is 1/16 of the DAC value used to generate the voltage that is fed into an OpAmp, and finally drives the PA FET’s.
For power levels of 1W and 5W I use the values from the calibration table (multiplied by 16).
For 2W, 3W and 4W I assume a linear relationship between PA drive level and output power, and this is reasonably accurate to about plus or minus 0.1W.
If people give me enough data points so that I know that the relationship needs to be slightly modified, I can make minor adjustments to this straight line calculation.
Below 1W, the power curve becomes increasingly exponential, so I’m using my own data points as a offset below the 1W calibration data point.
I doubt that the power output below 1W can be made totally accurate for everyone, but its probably good enough…
This change and the FM DTMF change are in the latest Tier2 file
I also made one more small change.
When a DMR call is received, if the call does not contain Talker Alias information which needs to be displayed on the bottom line of the display, either the Channel name or the Rx frequency is now displayed near the bottom of the screen using a small text size.
I initially displayed the Channel name in the same text font size as the Callsign + name, however this looked confusing, so I use the small text font size which is used for the zone name on the Channel screen.