Calibration of the transmitter power in the 2M band

SQ7ECZ
Posts: 10
Joined: Sat Mar 14, 2020 12:06 pm

Calibration of the transmitter power in the 2M band

Post by SQ7ECZ » Fri Jan 21, 2022 3:24 pm

There is a power difference for 2M and 70 cm band.
Two repeaters are in the same location.
One in the 2M band, the second in the band 70 cm.
REPEATERS use one antenna

BAFENG DM1801 gains access to them with settings:
1W - 2M converter, 0.5W - converter 70cm.
Tyt MD 9600 gets access to them with the settings:
10W - 2M, 1W - converter 70cm.
Both devices checked on the same antenna.
For a small power outgoing in a 2 m band or improper calibration.
In a week I will have a SWR + power meter.
I will check the outgoing power.
After setting the correspondence required for communication with the repeater, correspondents confirm the very good transmission quality.

G4EML
Posts: 919
Joined: Sat Nov 16, 2019 10:01 am

Re: Calibration of the transmitter power in the 2M band

Post by G4EML » Fri Jan 21, 2022 5:49 pm

If your radio is a V1 or V2 version then DMR will not work correctly at low powers, especially on VHF. This is a hardware design fault that cannot be fixed with firmware. V3 and later radios have different power control hardware which works a lot better.

All power levels are only approximate and there will be large variations between radios.
Power levels below 5W are likely to be very inaccurate.

The MD9600 is a high power radio, it was never designed to work at low power levels.

I1KDO
Posts: 27
Joined: Sat Nov 16, 2019 7:49 am

Re: Calibration of the transmitter power in the 2M band

Post by I1KDO » Fri Jan 21, 2022 6:10 pm

From tests in FM in VHF at 145.500 Mhz 50 Ohm dummy load they respect the set values ​​fairly, in UHF at 435.900 Mhz instead they are very low (less than 500 mw up to 5W then vary in default up to the maximum of 40 W which become 27w
They also change a lot according to the set frequency.
I will do further tests and table to be able to have comparisons with other radios.

73 lorenzo

G4EML
Posts: 919
Joined: Sat Nov 16, 2019 10:01 am

Re: Calibration of the transmitter power in the 2M band

Post by G4EML » Fri Jan 21, 2022 8:54 pm

Hi Lorenzo,

Thanks for the feedback.
Your UHF figures are different to my measurements on a V4 radio. On my radio the UHF power never goes below 1 Watt.

I think that just proves that anything below 5W is not going to be accurate unless people individually calibrate each radio.

The power is also very dependent on power supply voltage, especially on UHF. None of the radios I have seen have ever produced much more than 35W on UHF and at less then 12.0 V input the maximum is more like 25W.

Maybe we should not show the power level in Watts but just as levels 1-9 .

Colin.

G4EML
Posts: 919
Joined: Sat Nov 16, 2019 10:01 am

Re: Calibration of the transmitter power in the 2M band

Post by G4EML » Fri Jan 21, 2022 9:10 pm

I would also warn people against trying to get too much power out of the radio.

You are loading and testing this firmware at your own risk.

The firmware uses the factory calibration values for power up to the 40 W setting and should be safe.

The +W- power setting coupled with the User Power setting can result in power levels above this.
High values of the user power setting will cause high currents in the PA transistor and has the real risk of damaging it.

I would recommend that you do not use the +W- setting unless you know exactly what you are doing.

Colin G4EML

VK3KYY
Posts: 7475
Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia

Re: Calibration of the transmitter power in the 2M band

Post by VK3KYY » Fri Jan 21, 2022 9:38 pm

G4EML wrote:
Fri Jan 21, 2022 9:10 pm
I would also warn people against trying to get too much power out of the radio.

You are loading and testing this firmware at your own risk.

The firmware uses the factory calibration values for power up to the 40 W setting and should be safe.

The +W- power setting coupled with the User Power setting can result in power levels above this.
High values of the user power setting will cause high currents in the PA transistor and has the real risk of damaging it.

I would recommend that you do not use the +W- setting unless you know exactly what you are doing.

Colin G4EML
We should probably change the -W+ setting to be some other value than max PA drive

I have briefly tested the power output on -W+ / max drive and it was around 65W on VHF. However, the PA would probably oveheat quite quickly if anyone tried transmitting at that power level for any length of time, especially on FM.

On DMR heating would in theory not be so much of a problem, becuase its 50% duty cycle, but it depends on the effeciency of the PA FET and whether its being operated outside of its rating envelope.

On the GD77, I checked the FET specs, and it was rated for 6W, when the official maximum power output power level is 5W.

As far as I can tell the FET in the V5 radio is

https://www.mitsubishielectric.com/semi ... 70hvf1.pdf

Which is rated at "175MHz70W 520MHz,50W"


Never the less, I would definietly not recommend running the radio at high power, because the radio gets very hot, even on 40 / 50W if used for a long time.

I1KDO
Posts: 27
Joined: Sat Nov 16, 2019 7:49 am

Re: Calibration of the transmitter power in the 2M band

Post by I1KDO » Sat Jan 22, 2022 4:00 pm

HI to all
I am not very fond of high powers, I have always preferred to use enough energy for the connection, it would be better to remove the possibility of increasing the 45W value beyond its value (which are already many given the myriad of RPT with 10W output) in so that there are safety and avoid high absorption (8.37 A at 40W in UHF) there are also antennas .... let's use them
73 Lorenzo

SQ7ECZ
Posts: 10
Joined: Sat Mar 14, 2020 12:06 pm

Re: Calibration of the transmitter power in the 2M band

Post by SQ7ECZ » Sun Feb 06, 2022 4:12 pm

Finally, I have a power meter for the 2 m and 70 cm band.
I measured the power in both bands for the menu settings.
Here are the results:

Setting in the menu :
===================================================
100mW 250mW 500mW 750mW 1W 5W 10W 25W 40W
===================================================

Measurement for the 2m band

===================================================
- - - - - - 0,5W 6W 30W
===================================================

Measurement for the 70cm band

===================================================
0,1W 0,3W 1W 2,5w 5W 8W 16W 30W 35W
===================================================

Is this also the case with you?

G4EML
Posts: 919
Joined: Sat Nov 16, 2019 10:01 am

Re: Calibration of the transmitter power in the 2M band

Post by G4EML » Sun Feb 06, 2022 8:58 pm

Your 70cm results are probably normal. Your 2m results are a little strange but I am not too surprised. The variation between radios seems to be very large and even the factory calibration is not very accurate.

A more useful set of data would be to switch to the user defined power setting +W- and then vary the user power setting in the menu to produce a table of power setting to output power for each band. If we can collect enough examples from different batches of radios it might be possible to come up with a
better default setting.

Ideally this would need to be done across the whole frequency range but as this firmware is for amateur use only just one frequency in the 2m band and one in 70cm would be enough.

Colin.

VK3KYY
Posts: 7475
Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia

Re: Calibration of the transmitter power in the 2M band

Post by VK3KYY » Mon Feb 07, 2022 6:16 am

SQ7ECZ wrote:
Sun Feb 06, 2022 4:12 pm
Finally, I have a power meter for the 2 m and 70 cm band.
I measured the power in both bands for the menu settings.
Here are the results:

Setting in the menu :
===================================================
100mW 250mW 500mW 750mW 1W 5W 10W 25W 40W
===================================================

Measurement for the 2m band

===================================================
- - - - - - 0,5W 6W 30W
===================================================

Measurement for the 70cm band

===================================================
0,1W 0,3W 1W 2,5w 5W 8W 16W 30W 35W
===================================================

Is this also the case with you?
Did you test the power on 2m when running the official firmware ?

This would confirm whether the radio was correctly calibrated in the factory.

My experience with TYT is that they don't spend much time calibrating the power in each radio

Post Reply