A simulation of the final stage of a proposed 170 kHz transmitter was performed. The schematic is attached below.
A simulation of the final stage of a proposed 170 kHz transmitter was performed. The schematic is attached below.
The 5 pole output filter (L1, L2, C1, C2, C3) was designed for a 50 ohm input/output, Chebyshev response, and a cutoff frequency of 190 kHz. In the simulation, no accounting was made for the losses of these components.
Various values for L3 from 50 to 120 uH were tried with 90 uH appearing to give the best efficiency.
The input signal is a square wave of 3V amplitude at a frequency of 170 kHz. R3 was included to approximate the output R of a driver stage.
R2 is included to simulate the DC resistance of an audio transformer and this value is not critical.
The simulation data are:
V supply = 10 V.
VFINAL = 7.5 V.
I FINAL (through R2) = 124 mA.
PIN to final = 930 mW
Pload (R1) = 860 mW.
Efficiency = 92% (excluding inductor and capacitor losses).
A quick check of the harmonics on the output show they are down at least 30 dBc though a more careful analysis needs to be done for a final design.
So, it appears that this rather simple circuit can meet the design goals of a part 15 tx. operating near 170 kHz. This is only a feasibility study at this point but the results are encouraging.
In order to prevent fragmenting of the original thread ( http://www.part15.us/node/3006) on this subject comments have been disabled.
Neil