I've noticed some things that people are not looking at in relation to their mobile based repeaters. So I got bored and started playing around with Matlab and made a few graphs concerning common mobile radios that are used to build repeaters. This isn't a very extensive list as it only consists of most of the Motorola Radius line (includes Radius, Maxtrac, GM300, SM50/120, and M1225) as well as GE Custom MVP's. All of this was built off of data that is available in the service manuals. Even though I do own some Kenwood and Icom radios (I even have the data for Icom F221s and F420s that I measured off mine before my tablet crashed) I just don't have the service manuals currently. As I recover data or fix my tablet, I'll update with the F420 and F221 info for building Icom CY-420 and CY-221 repeaters.
These graphs show how transmit power relates to duty cycle (something that should honestly be considered when building repeaters). Figuring out the required duty is for the owner/builder of the system to decide. The duty cycle is a percentage of a 100s time period (as stated in both GE and Motorola service manuals). The slope of the lines represents the efficiency of the transmitters, this can be used by both those building off-grid systems and for calculating heat produced. These numbers can be changed with other methods of cooling (air flow, heat sinking, etc.) but represent the environment the manufactures designed the equipment to operate in.
Motorola designed the 40W radio for a 15% duty cycle, which translates to 2000 kJ of heat for the chassis. Giving duty cycles as follows.
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The efficiencies for the different power levels are as follows:
25-40W = 23.2%
10-25W = 24.1%
1-10W = 18.1%
GE Custom MVP
GE designed the 35W radio for a 20% duty, which translates to 2160 kJ of heat for that chassis. The 25W and 5W radios are lacking something…the heat sink on the back of the 35W radio (it can be replicated with a P4 or similar CPU heat sink). As such there are two graphs for the 25W radio, one for a factory radio (20% duty @ 25W = 1160 kJ of heat) and one for a system with the heat sink.
GE.jpg 33.84KB 1 downloads
The efficiencies for the power levels are as follows:
21-35W = 24.5%
7-25W = 29.1%
Again, all these were taken off numbers available in the service manuals.