stereocoder FRM 83

[lorenzo44]

Hello my friends.
Here is the schematic of the stereo coder frm 1983 see in the magazine free radio magazine.
To replace lm741 by lf 356 for a better quality audio.
pcb and parts list has to follow

codeur stereo frm 1983.jpg

[lorenzo44]

pcb of stereocoder frm

[lorenzo44]

pcb components

[lorenzo44]

photo of stereocoder frm

[RF-Head]

Lol the design that my father made in the begin 80s
MPX filter was made by Ivo Maatman
Later the design changed and sold by a shop callled Eddy's Electro Shop
There was even a PLL stereo 5W fm transmitter
I will look for the pcbs and make some pictures
Maybe Albert know what im talking about

[Albert H]

I remember Jose and Alfred at FRM! The stereo coder was OK for its day, but over in the UK, we were using the MC1496 to generate the DSSC signal for the "S" component, and another '1496 to generate the 38kHz carrier by frequency doubling the 19 kHz pilot.

Another trick I discovered in those days - for a "switching" coder - was to use a lightly loaded 455kHz ceramic filter in a FET oscillator to generate 456kHz. Divide by 12 for 38 kHz and by a further 2 for the 19kHz pilot. This was the cheapest way of generating the signal needed for a coder at that time.

[MC Spanner]

I used the ceramic "resonator" trick in a small number of coders produced around 1990. I found it to be a false economy, as it didn't work with all filters - you usually had to try a handful before you'd find one that would have it! As I recall there was also quite a significant effect due to temperature, but I'm prepared to admit that could have been poor choice of components in my oscillator circuit...

[Albert H]

Spanner:

I had a boxful of 455kHz filters made by Murata. These were fine, but you had to use NPO capacitors in the oscillator (and a regulated supply) to get good stability. They were three-terminal types, and the "ground" terminal went to the source of the oscillator FET. Pins 1 and 3 of the filter went to the gate of the FET and ground. There was a 68pF gate to ground, in parallel with a 220k resistor. The output signal (using a 9V regulator) was about 5V p-p, which would drive the CMOS divider directly. The 19 (and 38) kHz signals were within a couple of Hz over quite a wide temperature range. When I ran out of these filters, I moved over to using 4864 kHz rocks from AEL.