Home › Forums › temp › New SSTRAN AMT5000 High Efficiency Transmitter Preview › Can you comment on range
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The short answer is the range of the AMT5000 will be equal to or better than any other Part 15 compliant AM transmitter. That’s a bold statement, so here is the supporting technical information.
Transmitter range is a complicated issue that depends on the transmitter output power and the installation-specific antenna and ground losses. FCC rules limit the final RF stage power input to 100 mW. For any given antenna and ground system, the “best range” prize will go to the transmitter that is able to convert the largest portion of the 100 mW input power to output power. Percent Efficiency = 100 * output power / input power.
Choosing the point in the circuit where efficiency is measured is critical to evaluating the real efficiency of a transmitter.
The efficiency of the RF output transistor is the first part of the overall efficiency calculation. Output transistor efficiency is a measure of the amount of input power that is lost as heat in the output transistor. The AMT5000 transistor efficiency is 98%, so only 2% of the input power is lost as heat. The MOSFET transistor runs cool to the touch. No heat sink is required. The transistor is rated at 2 watts dissipation (not because it has to, but because it can), so it is not stressed at all.
Beyond the output transistor, on the way to the antenna, is the tuning coil. Whether or not the tuning coil losses should be considered in measuring the overall efficiency of a transmitter has historically been controversial on the various part 15 forums. Some transmitters don’t have a built-in tuning coil and some do. If the tuning coil is built-in, there is no option but to include its losses in the overall transmitter efficiency calculation. If there is no built-in tuning coil, then the losses in the external tuning coil should be included for an apples-to-apples comparison.
The AMT5000 has a built-in tuning coil in the form of an iron-powder core toroid coil. Toroid coils offer major advantages over other coil configurations occupying the same physical volume, but only if the core material is properly chosen for the operating frequency and power level. Some power is inevitably lost in the core. It is extremely important to carefully choose the core material that yields minimum loss. There are literally dozens of different core materials available, tailored to switching DC power supply frequencies way up to hundreds of MHz. Most people think “ferrite” when they think of toroids, but ferrite is a poor choice for transmitting at AM broadcast frequencies. Certain “iron powder” cores are best suited for the AM band. The AMT5000 uses the optimum iron powder core material to minimize core loss.
If the optimized built-in toroid tuning coil isn’t the Holy Grail for the die-hard experimenter, it can be bypassed in the AMT5000 with one jumper. You can use an external loading coil, or any form of externally tuned antenna. Large air-core coils, way to big to be practical inside a transmitter box, can be connected. You can experiment with base-loaded, center-loaded, top-loaded, helical or any other conceivable type of tuned antenna.
In summary, the overall efficiency of the AMT5000 will be equal to or better than any other Part 15 transmitter utilizing an internal tuning coil, and the overall efficiency will be essentially the best theoretically possible when using any conceivable super-efficient, externally tuned antenna system.