success with changing modulator settings !
Both modulators (vision and sound) are programmed via I2C, and the appropriate bit sequences to be generated by the
FPGA are found in Frank's program. He helped me understand what is what.
As a preparation for a different standard, I tried to program the modulators for different modulation and RF frequencies.
With Frank's help and carefully studying the modulator IC's datasheet I eventually managed to understand how the bit-sequences should be for my particular needs, and I managed (with trial and error - a good way to learn something) to get the wanted RF frequencies and other settings. The block diagram of the modulator IC (found in the data sheet) helped a lot in understanding the internal dividers and pre-scaler.
The 567 line standard has FM sound, and the vision to sound carrier distance is 4.5 MHz.
Luckily this value was directly possible in the used MC44BS373 modulator IC.
IC5 is the only modulator IC that is required to work for the 567 line standard. In the case of 405 lines, AM modulation of the sound carrier at 3.5 MHz is required, which the MC44BS373 cannot generate. So for that an additional IC (IC4) is used. It is achieved the same way in the Aurora standards converter.
But not required for 567 lines also.
IC4 (the original sound modulator IC) kan be switched off with DIP-switch SW8B.
This works fine.
But I also want(ed) to switch off IC4 in the software.
Frank has helpfully sent me some information and I am now studying the program lines, but so far I have not been able to achieve what I would like to.
Until I manage to get this working, I just put the RF frequencies of IC4 out of harm's way by programming well out of band RF settings. So even when the audio-modulator DIP-switch SW8B is OFF (i.e. unwanted RF generated by the "sound" modulator IC4), there is no interference in the wanted signal.
Eventually I hope to understand how the relevant program lines are working exactly and be able to switch off IC4 in the program itself.
I have aligned my three working 567 line sets to receive and display 625 line pictures at channel E3 or E4, so these channels are also useful to have. E3 and E4 are also very handy to use the Hegdhog just as a modulator for my 625 line sets.
By the way, the definite required 567 RF frequencies are very close to channel E4, but with 4.5 MHz i.s.o. 5.5 MHz V-S distance.
The 4.5 MHz V-S distance also now works well. I could confirm this on a Panasonic TR1001S micro TV which has the possibility to receive USA VHF channels (they have the 4.5 MHz V-S). The continuous tuning of the older TVs helps in this, because the channel frequencies are different for various standards.
A simple test picture (internally generated by the MC44BS373) on channel E4 - was my first result:
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attachment=18641]
In the end I will program a small range of frequencies around the center frequency, to have a kind of fine tune.
The local oscillator in the 567 line sets has a relatively large drift during the first half hour of warming up, and a possibility to adapt the modulator RF frequency (sound mainly) is welcome during this period.
The required step size will be defined experimentally. The MC44BS373 can only generate frequencies at certain distance, but the step size is small enough for this purpose.
More to come (most likely with lots of additional help).
Thanks again Frank for all your support!
Jac