M1225 - unable to toggle between High/Low power?

[g8tzl2004]

I have successfully programmed a VHF M1225 onto 145 MHz with 12.5KHz spacing using the shift key trick.

The radio works fine with good sensitivity at 145MHz. TX power output is about 25W compared to 40W for an "in band" frequency(ie 150-174MHz).

However, I am unable to get the High/Low TX power toggle button to operate. The power is always at the maximum (ie 25W for out of band and 40W for in band freqs)

I have correctly programmed the High/Low front toggle key. I have also tried removing the High/Low toggle key and programming one freq to Low power. Again, the TX power output remains at the maximum.

Maybe the problem is due to the fact that I have programmed the set "out of band". Maybe this has upset the TX Power Calibration? I have checked the values for TX Power Calibration and they seem to be OK ie. range from settings of 134 - 156 for Low Power and 169-203 for high power.

I guess all the High/Low power toggle is doing is reducing the drive level by about 2dBm [a 7dBm reduction would probably have been more useful ]

The local/distance RX toggle seems to work - although its not very obvious - you need a very very weak signal to notice any effect - again maybe this is due to programming the radio out of band. I have also set the 12.5Khz squelch setting at "5" compared with the original setting of "12".

Any thoughts?

Thanks

[Al]

If you are taking the radio out of its rated bandsplit, as many others have done by using the shift key with Maxtracs and GM300s, all bets are off on the power levelling circuitry in the radio working properly. Others have found that when programmed for out-of-rated-bandsplit operation the internal power levelling/calibration circuitry was nonfunctional, probably due to the radio's firmware power calibration tables not having the required number of entries needed for out of band operation. My guess would be that the high/low power setting is being switched/controlled properly but the firmware is confused and just sets a default value to the DAC that controls the power calibration loop because of the out of band operation.

[g8tzl2004]

Thanks for the reply Al.

I've just noticed from "cold" , the radio initially puts out about 10W for 1 second , this then rises to 15W over a 2 second period. Then after about 5 seconds at 15W , the power quickly jumps to 25W. After this (ie from "warm") , the radio always puts out 25W.

Do you think this is a feature of the "Out of band" TX calibration routine. Or maybe the TX VCO is on the verge of going out of lock?

Is it worth lowering the TX power calibration levels? Maybe at 145MHz , the "Low" TX calibration levels are way too high?

Also, if the radio was operating in-band , would it be possible to lower the "Low" TX level to run at , say , 5W rather than 25W , or would that upset things. I'm sure switching from 25W to 40W does not actually make much difference !!

Thanks