Re: Simple System A Band I Modulator - (No Processors)
Hi Everyone,
here is a follow up to this project. I made a few changes in order to unify component values. A switch to turn off the audio carrier was added and I made a PCB board for the project using SMD components. This allowed me to make a very small device that fits in a readily available aluminium housing.
The whole circuit runs on 5V so a regular mobile phone charger can be used to power the unit, therefore, I added a micro USB port as a power input. Also powering from a PC or laptop is possible. This might be of interest to those of you who use a PC to output 405 signals at shows or in the field.
The project was made in KiCAD. Please contact me for the project files. I used a dual layer PCB but the top layer is only ground. Since I can only do single sided PCBs at home I etched only the bottom side and soldered several wires through the two layers in order to connect the top an bottom ground planes. This worked very well and was easy to do.
Attached you can see the finished modulator in its box. I also included a scope image of a modulated staircase signal with the audio carrier switched off. This nicely shows the linearity of the signal. The singal level on peak white is about 150mV into 75Ω so it can drive many TVs...This test signal is a 625 signal but I am waiting for parts to build Frank C.s "Picgen" generator. One plan I have is to combine the Picgen and a modulator on one PCB to have a source for RF test signals in one small box powered from a USB charger.
Semir
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