Addition power settings?

VK3KYY
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Addition power settings?

Post by VK3KYY » Wed Jan 29, 2020 9:21 pm

I've been sent an update that removes the 750mW power level but adds 50mW as the lowest option instead

I don't know whether the 750mW setting is of any use to people and whether if the 50mW setting is added the 750mW setting should be retained.

the step of 500mW to 750mW is only approximately 1.5dB, so perhaps is not important.

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DG1YFX
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Re: Addition power settings?

Post by DG1YFX » Wed Jan 29, 2020 9:52 pm

Sounds fine to me. But since there is a large variation in power levels on different GD-77s I would like an option where one can set the output level freely. Somewhat like in the beginning of OpenGD77. Maybe an "Expert Menu (Enter at your own risk)". Just a thought.

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Jens

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m1dyp
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Re: Addition power settings?

Post by m1dyp » Wed Jan 29, 2020 10:03 pm

hi, maybe keep the 750 and add a 100 , so 100, 250, 500, 750, 1, 2, 3, 4, 5

just my thoughts

probably not that important.
73 de Ken :D

VK3KYY
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Re: Addition power settings?

Post by VK3KYY » Wed Jan 29, 2020 10:10 pm

DG1YFX wrote:
Wed Jan 29, 2020 9:52 pm
Sounds fine to me. But since there is a large variation in power levels on different GD-77s I would like an option where one can set the output level freely. Somewhat like in the beginning of OpenGD77. Maybe an "Expert Menu (Enter at your own risk)". Just a thought.

73s
Jens

Radioddity (actually TYT who make the radio) don't seem to calibrate the power levels very accurately and put that data into the calibration table.

Originally the firmware allowed people to set the power on a continuously variable scale between 0 and Maximum PA drive.

However most people found this very confusing, because the PA drive level -> power output in Watts, is not linear. Also the power output varies depending on the band (VHF/UHF) and also the frequency in the band.

So every time you change frequency or band you would also need to manually change the power level. Especially as on VHF, its possible to overdrive the PA quite easily, and perhaps do some damage.

With the current system, if people calibrate their radios, the power output will be approximately correctly to around 10%

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Re: Addition power settings?

Post by VK3KYY » Wed Jan 29, 2020 10:17 pm

m1dyp wrote:
Wed Jan 29, 2020 10:03 pm
hi, maybe keep the 750 and add a 100 , so 100, 250, 500, 750, 1, 2, 3, 4, 5

just my thoughts

probably not that important.

Getting power levels of 1,2,3,4,5 would be very difficult. In fact any power level below 1W is not super accurate

The power curve on the PA highly non-linear between 0W and 1W, and becomes a bit more linear between 1W and 5W.

i.e Below 1W, the mapping between drive level and output is almost exponential.
Between 1W and 5W, the curve goes in the other direction and is much flatter.

My digital power meter seems to stop registering any power below around 50mW, and I think its probably inaccurate below 250mW

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Re: Addition power settings?

Post by VK3KYY » Wed Jan 29, 2020 10:17 pm

VK3KYY wrote:
Wed Jan 29, 2020 10:17 pm
m1dyp wrote:
Wed Jan 29, 2020 10:03 pm
hi, maybe keep the 750 and add a 100 , so 100, 250, 500, 750, 1, 2, 3, 4, 5

just my thoughts

probably not that important.

Getting power levels of 1,2,3,4,5 etc would be very difficult. In fact any power level below 1W is not super accurate

The power curve on the PA highly non-linear between 0W and 1W, and becomes a bit more linear between 1W and 5W.

i.e Below 1W, the mapping between drive level and output is almost exponential.
Between 1W and 5W, the curve goes in the other direction and is much flatter.

My digital power meter seems to stop registering any power below around 50mW, and I think its probably inaccurate below 250mW

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m1dyp
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Re: Addition power settings?

Post by m1dyp » Wed Jan 29, 2020 10:31 pm

leave it as it is then :mrgreen:
73 de Ken :D

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Re: Addition power settings?

Post by VK3KYY » Wed Jan 29, 2020 10:42 pm

These are a couple of power curves for 2 different radios. Both on UHF (437Mhz)

As you can see the drive level number 0 - 4191 (The PA control uses as a 12 bit DAC) needed to produce a specific power, varies a lot between each radio and hence why the calibration contains reference PA drive levels for 1W and 5W for 5Mhz wide chunks of the entire frequency range.

But the calibration only stores the reference value in a single binary byte, which is 8 bits, and is 16 times less resolution than the actual PA control DAC.

If you try to extrapolate the values below 1000mW, you'll see how difficult it is to set an accurate power level with the constraints of a relatively low resolution calibration data, and a highly exponential power curve

Vertical scale is power in mW, horizontal scale is PA drive to the DAC.
power_curve.png
power_curve.png (26.92 KiB) Viewed 767 times

kt4lh
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Re: Addition power settings?

Post by kt4lh » Wed Jan 29, 2020 10:49 pm

Have you ever done any power usage measurements at the various power levels? I know I've seen some other radios that lowering the power into the finals below factory settings did not actually use any less power. But I'm all for 50mW low, I can touch my hotspot from my chair. :)

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Re: Addition power settings?

Post by VK3KYY » Wed Jan 29, 2020 10:58 pm

kt4lh wrote:
Wed Jan 29, 2020 10:49 pm
Have you ever done any power usage measurements at the various power levels? I know I've seen some other radios that lowering the power into the finals below factory settings did not actually use any less power. But I'm all for 50mW low, I can touch my hotspot from my chair. :)
I've not actually looked at the current taken at the various power levels.

I agree the 50mW level is a nice thing to add, and perhaps we should retain the 750mW setting.

We could also have a setting where the PA was completely off, but the RF chip will radiate some power even if the PA is off, especially as the case of the radio is not shielded.

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