17-03-2017, 09:07 AM
(17-03-2017, 02:01 AM)Nowhere-Man Wrote: I referred back to Lawrence's summary of the Saalburg circuit. The main areas of focus for me at the moment are the two IF's and the EBF89 plus the EABC80. I am literally racking my brains to trace the diodes and, of course, there is the discriminator circuit. I think Lawrence indicated the centre tap between L23 and L24. Anyway maybe it will be understood why I take time out to address textbook theory. Discriminator circuits won't be understood without some grappling with ARRL tutorials.
I haven't fully grasped Lawrence's explanation yet but I will get there. Tomorrow I will print it.
Notice one diode on EBF89 is grounded out and the grid used instead. Likewise the diode on EABC80.
The Foster Seeley discriminator circuit may help me if I locate it.
When I step back and say all the circuit makes sense, then I will go to work more fully.
It might help you understand better if you print out a copy of the schematic and highlight the AM and FM signal paths with two different coloured marker pens.
The EBF89 contains two diodes but only one of them is used, the one that is used is used for AM detection and it also provides the AGC voltage, the EABC80 contains three diodes but only two of them are used, those two that are used are used for FM detection, the FM detector in the Saalburg is of the ratio detector type, it's not a Foster Seeley type, the Foster Seeley type needs a limiter stage before it.
It might also help by analyzing schematics in block/stage form by recognizing chunks of circuits and understanding what their function is, ie: what goes in and what comes out.
Lawrence.
