Power Levels vs. Battery voltage vs. dif. Radios

[OE5DMF]

Hi.

i just got my 3rd GD77 and noticed that the TX Power at 50mW is about 800mW so i did some measurements.

Here is the link to my Results of a 2 Radio comparison:
https://docs.google.com/spreadsheets/d/ ... sp=sharing

perhaps this helps in future development. i just wanted to share it with you guys.


(Thanks for the UserPower setting!! helped a lot)

Markus OE5DMF

[VK3KYY]

Hi.

i just got my 3rd GD77 and noticed that the TX Power at 50mW is about 800mW so i did some measurements.

Here is the link to my Results of a 2 Radio comparison:
https://docs.google.com/spreadsheets/d/ ... sp=sharing

perhaps this helps in future development. i just wanted to share it with you guys.


(Thanks for the UserPower setting!! helped a lot)

Markus OE5DMF

You need to change the calibration of the radio

Use the OpenGD77 Calibration screen.

If you set the 1W and 5W values then the 50mW will be more accurate.

Actually, you only need to set the 1W calibration, becuase the PA drive voltage used for 50mW is a proportion of the value for 1W, which comes from the calibration table data.

[OE5DMF]

Thank you for your Comment.

What i did:

• Removed the Battery and connected the Radio to a benchtop power supply (6.4V, 7.4V, 8.4V)

• connected the Antenna Connector through a 60dB Attenuator to the Spectrum Analyzer

• set TX Power to +W-

• set the Frequenzy to 145 MHz, 435MHz

• set "User Power" - Settings Menu from 0 to 4100 (4096)

• Every "User Power" step i measured the output power

in trx.c:
Line 997: Case 9: User Power is set 1:1 to txDACDrivePower. No Power clibration Data is used in this mode. Am i right?

Code: Select all

		case 0:// 50mW
		case 1:// 250mW
		case 2:// 500mW
		case 3:// 750mW
			txDACDrivePower = trxPowerSettings.lowPower * fractionalPowers[trxCurrentBand[TRX_TX_FREQ_BAND]][txPowerLevel];
			break;
...
		case 9:// 5W+
			txDACDrivePower = nonVolatileSettings.userPower;
			break;

My conclusion:

• as my measurements show the minimal possible tx power has nothing to do with the calibration data. (i know 50mW is trxPowerSettings.lowPower * 0.59, but im am talking about hardware limits not software settings)

• and the radios vary a lot from device to device.

• and the newer batches are not able to go very low on tx power

[F1RMB]

Hi,


Roger meant calibration screen in the CPS (Extra menu).


Cheers.
---
Daniel

[OE5DMF]

Hi,


Roger meant calibration screen in the CPS (Extra menu).


Cheers.
---
Daniel

I know Daniel. You are right.
This is the "trxPowerSettings.lowPower" value in code and is not used in "User Power" mode as i mentioned.

User Mode writes the 12bit DAC Value (0-4096) direct to the output stage without software calibration (Which is a 0-255 interpretation of the DAC value)

Thats how i see the situation. @VK3KYY please correct me if i am wrong.....

[F1RMB]

The case #9 in trx is simply set the DAC value from the one the user entered in the options menu (no fractionnal computation).
So, check your output power on 1W and 5W, it's probably off, and the reason why 50mW (and probably 250..750mW) is so high on your transceiver.


Thanks.
---
Daniel

[G4EML]

Markus, I think Roger and Daniel have not realised exactly what and how you are testing.

I agree with your conclusion that some radios will never be able to output very low power levels.

The minimum power level that a radio can send is defined by the level it outputs with a DAC value of Zero. As you have demonstrated, that varies a lot between radios and probably depends on the batches of components used. Some may be able to go as low as 50mW but some, like yours, may not be able to go much below 1W.

It is probably wrong to display absolute power values on the radio, they can never be very accurate. Max, High, Mid, Low and Min would probably be more appropriate to display.

Colin G4EML

[F1RMB]

Hmmm, Okay.


But I didn't see any DAC -> measured power list here.
Also, stupid question, but what is your measurement setup ?


Cheers.
---
Daniel

[VK3KYY]

In the original post you said

TX Power at 50mW is about 800mW

This implies that you are using the 50mW setting not the -W+ setting, and that at that setting the 50mW power is outputing was 800mW

I'd almost say you radio has a fault, if setting the DAC value to 0 still outputs 800mW.

[OE5DMF]

Hmmm, Okay.


But I didn't see any DAC -> measured power list here.
Also, stupid question, but what is your measurement setup ?


Cheers.
---
Daniel

Your Question 1:

Here is the link to my Results of a 2 Radio comparison:
https://docs.google.com/spreadsheets/d/ ... sp=sharing

Your Question 2:

What i did:

• Removed the Battery and connected the Radio to a benchtop power supply (6.4V, 7.4V, 8.4V)

• connected the Antenna Connector through a 60dB Attenuator to the Spectrum Analyzer

• set TX Power to +W-

• set the Frequenzy to 145 MHz, 435MHz

• set "User Power" - Settings Menu from 0 to 4100 (4096)

• Every "User Power" step i measured the output power