Initial Testing and Tuning
Initial Testing
As seen in the picture above this transmitter was initially ‘brought to life’ on the test bench using a dummy load. The newly homebrewed VFO and station T/R sequencer were also used to verify that all interlocks were working correctly.
The modulator efficiency board protection circuits were calibrated using the recommended initial settings for modulator output voltage and current gain and current zero.
Gate waveforms were verified, and drain waveforms were checked at low and then high power. The first failure occurred early, when a .15uf bypass capacitor on the rf deck failed, taking a 130v transorb with it. The failed components were replaced and the transmitter was back on line at low power. The .15uF capacitors were subsequently replaced with devices that can handle more current, and high power was tested again.
The modulator efficiency board protection circuits were calibrated at transmitter rated high power.
FQA11N90 75m Gate Waveform
FQA11N90 160m Gate Waveform
Drain Waveform
New Station
The transmitter was subsequently moved to its new station location, and wired to station antennas and its audio chain. KD3CN was now on the air with a much improved AM signal!
Tuning Up at High Power
As shown here, initially the tuning capacitor was about half meshed on 75m. This caused some arc-over of the capacitor on modulation peaks. The 75m coil was tapped to remove 2 turns, and subsequently the tuning capacitor was approximately 80% meshed when tuned on 75m and 160m. This change alleviated the arc-over problem.
The modulator efficiency board protection circuits were again tweaked at transmitter rated high power for current gain and current zero. This was done to prevent trips during high modulation peaks
The transmitter was designed by Steve Cloutier WA1QIX. Information on this design may be found at www.classeradio.com