I have a topic going on concerning the Chris Cuff AM C-Quam Stereo Transmitter.
I have asked Chris Cuff for permission to share these with the group here, so everyone has an idea of how this transmitter is designed. Permission was granted for me to share these here at part15.us by Chris Cuff.
Below are schematic diagrams that cover the whole kit design.
Although the images in this post are not clear, below are the links to each image, click those to see a decent copy with magifying capabilities for a better clearer view of each schematic diagram.
Bruce.
The rf output stage looks wrong,
The diagram shows the transistor base is biased from a 56k resistor to the 12-20v supply ?
I would have at least expected the base bias to come from at least 2 resistors, so without rf drive, the collector would sit at half supply, as this has to be a linear amp.
Also the rf out has no matching network to load the antenna properly.
An oscilloscope is essential here.
BTW, most of this circuitry is VERY similar to 2 other c-quam exciters i have !
Paul.
Yay! Thanks especially to Chris Cuff for allowing those diagrams to be published here, and to Mr. Bruce for being the conduit bringing them to Part15 (US). I was waiting and hoping you'd get approval.
I believe that Alfredo, and especially "Alfredo Lite" are the origin circuits to several of the CQUAM transmitters out there now, but the Alfredo design goes back maybe 20 years! It was designed as a complete, versatile transmitter system using CQUAM techniques, and there was a whole website about the transmitter on his school's server at the time. It was the only in-depth page on AM stereo to be found. It had schematics for each section of the transmitter, plus explanations of what was going on.
The Alfredo is a full unit that's broadcast spec, with an ovened crystal, overmodulation alarm flasher, 3-band limiter, 10 khz low pass filtering, final clipper with asymmetrical modulation, with a limiter bias supply. Kind of cool how this one has double regulation of the 5 volt supply, from the 9 volt supply.
I gave the output circuit a quick look BOARDMAKER, it looks like it's going for class A with a dynamic collector resistance, reminding me of the Wein oscillator in my old audio generator, using the dynamic resistance of the bulb. That final wasn't on the original design, it only went as far as the push-pull output, which is supposed to be 10 milliwatts.
The original post was posted here in order to overcome a limitation of our forum system on posting images and, very appropriately, makes them available for discussion.
In order to keep the the posts about the Cuff Stereo Transmitter together in one place please make your comments in the original thread on this topic: http://www.part15.us/forum/part15-forums/transmitter-talk/chris-cuff-c-quam-am-stereo-transmitter-discussion
To facilitate this, this thread is locked.
Neil