Batboard

I need to program a CDM750 lowband for less that 10 watts output. I have seen one that puts out 6 watts so I know it can be done.

I have the CPS and Tuner but lack that algorithum.

read the radio, go to the radio configuration tab, then select tx power and in those two boxes put the wattage output you want in the boxes, put 6 watts in the high side and 5 in the low side and write that to the radio and you should be in business.

I'm going to take it that you're not concerned about the spurious transmissions that plague radios putting out 10% of their rated power

escomm wrote:I'm going to take it that you're not concerned about the spurious transmissions that plague radios putting out 10% of their rated power

According to Motorola (when I was talking to them at the system support center) the CDM series is built to put out down to 5 watts with no spurious emission issues. I've never had a problem with them, even checking with a spectrum analyzer.

Todd

wavetar wrote:

escomm wrote:I'm going to take it that you're not concerned about the spurious transmissions that plague radios putting out 10% of their rated power

According to Motorola (when I was talking to them at the system support center) the CDM series is built to put out down to 5 watts with no spurious emission issues. I've never had a problem with them, even checking with a spectrum analyzer.

Todd

Yes, but you're doing it right, by checking with a spec-an. In general, if you're going to significantly alter the intended performance of an RF device (backing the power down to 15% of rated counts)... you should give it a full checkout with proper, calibrated test equipment. This will keep you and your company safe from liability and criminal issues for interference.

Thanks for info all. However let me provide a few details. This is a low band 32-72 watt CDM750. The CPS will not let me enter a value below 32 watts.

I was told that I would need to use the tuning software and change the bias voltage to bring down the output?

FYI, I have two low band Fire repeaters each with two CDM750's and a TE Systems power amplifirer which requires a maximum of 10 watts input. The North site works ok with a CDM750 output of 6 watts. However I am repairing the South site and I cannot get the wattage down.

Power is rated @13,8 volts. If you drop voltage to 12 volts or less, power drops also. It's cheap and easy!

Ed

wavetar wrote:

escomm wrote:I'm going to take it that you're not concerned about the spurious transmissions that plague radios putting out 10% of their rated power

According to Motorola (when I was talking to them at the system support center) the CDM series is built to put out down to 5 watts with no spurious emission issues. I've never had a problem with them, even checking with a spectrum analyzer.

Todd

Not to mention that I doubt Motorola would put the option of turning the power down in the CPS if the radio was spurious at those power levels.

wavetar wrote:

escomm wrote:I'm going to take it that you're not concerned about the spurious transmissions that plague radios putting out 10% of their rated power

According to Motorola (when I was talking to them at the system support center) the CDM series is built to put out down to 5 watts with no spurious emission issues. I've never had a problem with them, even checking with a spectrum analyzer.

Todd

Cool, I did not know that. This is exactly why I love batlabs

I do know that when I took over a new customer, their base radios were putting out 5watts, causing all kinds of havoc, but they were using M1225-LS radios and not CDM series. I will keep that in mind for when they upgrade

Always a must do when lowering the TX power is to check with a spectrum analizer and different loads to make sure the TX does not spur.

I always check with 25, 50, 75, and 100 ohm loads.

Will wrote: I always check with 25, 50, 75, and 100 ohm loads.

Pardon my asking, but why? The radio circuitry is only meant to interface to 50-ohms, and there are no printed specifications from Motorola indicating how the radio would act under any other. The fact the radio might produce spurs when connected to an improper load has nothing to do with how it acts otherwise.

Todd

Well Mr. Todd,

The moble radio transmitter needs to be able to opperate correctly into mild mismatches, and that is part of transmitter PA design. Motorola Mobile transmitters in the Maxtrac and later mobiles will work into mismatches as great as 2:1 without breaking into spurious operation at rated power output. Not always at reduced power output, <40%.

When using a mobile to drive a power amplifier at reduced power output as the orig posts refer to, the load on the transmitter may NOT be even close to 50j0 ohms.

Then again it may be more correct to use a attenuator pad between the mobile and the power amplifier. Then I would not need to test the mobile into the extreme mismatches to test for spurs.