Performance of modern AM modulation methods into varied antenna conditions

In order to achieve the best possible signal quality and maximum coverage it is important to understand how different modulation methods perform under varied antenna conditions. This paper examines the performance of PDM and digital modulation into three different narrow band antenna conditions. Each narrow band antenna condition presented a 1.4:1 VSWR at the +/-10 kHz sidebands. The digital transmitter used for the test is the Harris DX10 which uses a 12 bit digital synthesis modulation method. The PDM transmitter used was a Harris Gates 2 which uses polyphase pulse duration modulation. The most important difference between the two transmitter designs is that the DX transmitter does not require a PDM low pass filter between the modulator and power amplifier to eliminate the PDM switching frequencies.