I have a UHF 40 watt CDM-1550 in the ham band that I am using as a low power link between repeater sites. 40 watts is wayyyy to much power for this LOS link and I would like to get the power out down to 10 watts or less is this possible??
Thanks,
Rory Bowers, K6CKS
CDM1550 Power Control
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Re: CDM1550 Power Control
Not without making spurs
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SteveC0625
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Re: CDM1550 Power Control
I don't think you can push them down below 20 watts or so in the CPS. Radio Configuration --> Tx Power tab.RoryB wrote:I have a UHF 40 watt CDM-1550 in the ham band that I am using as a low power link between repeater sites. 40 watts is wayyyy to much power for this LOS link and I would like to get the power out down to 10 watts or less is this possible??
Thanks,
Rory Bowers, K6CKS
The 25 watt models can set right down to 1 watt in the CPS. I am not sure if that will create spurs, however.
You might keep your ear to the ground for a 25 watt CDM750, 1250, or 1550.
Re: CDM1550 Power Control
The 25-watt model is rated for 1-25 watts and can safely be run down to 1 watt.
The UHF 40 watt is rated for 25-40 watts (the VHF is 25-45 watts).
As was stated, going below the rated power can result in spurious emissions.
If you want to knock down the power below the rated minimum, you will need to add an attenuator.
The UHF 40 watt is rated for 25-40 watts (the VHF is 25-45 watts).
As was stated, going below the rated power can result in spurious emissions.
If you want to knock down the power below the rated minimum, you will need to add an attenuator.
Re: CDM1550 Power Control
That is interesting... going through the softpots in Tuner32 I found that I can slide the power back to something in the milliwatts. Watching the spectrum analyzer on my service monitor I saw no appreciable increase in spurious harmonics. At the 10 Watt level from one end of the spectrum (403 Mhz) to the other (469 Mhz) the spectrum was clean and free of harmonics. So, having that in mind I am still wondering if there might be a small change in a component value that will allow the radio to operate at 10 watts?? I don't want to redesign the PA, I just want to swamp it a little 
Re: CDM1550 Power Control
If you want to have a nice paperweight go ahead and turn the power down. Or you can listen to the numerous people telling you not to do that and use an attenuator or get the right model radio. The choice is yours. You are going to have spurs, you are going to draw more current than needed, and you are going to overheat components inside the radio, by turning it down that far. I suspect you'll be here asking for help how to fix it sooner rather than later if you do run your power that low as a link transmitter.
Re: CDM1550 Power Control
You can perform surgery on the RF input pin and solder an attenuator from the buffer output to the RF input pin.
Best method is to obtain a low output radio as suggested. Those nasty spurs will come back to bite you when you least expect it.
Even a decent power attenuator requires a constant flow of cool air, creates heat and prone to failure at the wrong time, especially when under constant stress of thermal heating and cooling.
Just locate a low power radio and forget all the B.S that comes with it, for your application.
Although a good isolator may help lowering those spurs, a dual isolator, that is. with a pair of 60 watt loads.
Best method is to obtain a low output radio as suggested. Those nasty spurs will come back to bite you when you least expect it.
Even a decent power attenuator requires a constant flow of cool air, creates heat and prone to failure at the wrong time, especially when under constant stress of thermal heating and cooling.
Just locate a low power radio and forget all the B.S that comes with it, for your application.
Although a good isolator may help lowering those spurs, a dual isolator, that is. with a pair of 60 watt loads.