10-10-2020, 03:34 PM
I have spent some time on the modulator side of this project. So far I have:
30 to 900 MHz in 250 KHz steps vision modulator.
Selectable Positive video modulation AM sound / Negative video modulation FM sound
Selectable 3.5, 4.5, 5.5, 6 and 6.5 MHz sound. 3.5 MHZ is AM only
That will cover most channels. The only one that I can think of that it wont is the French system E. Can anyone think of any others?
I may try doing a special for system E but I am not sure how well it will fit with the available dividers. I haven't done the maths on it yet.
The MC44BS373 data sheet don't explicitly state the UHF frequency range. That is something that I have been caught out with before.
It just says "Channel 21–69 UHF operation" It also says "VHF range possible by internal dividers (30–450 MHz)"
The smallest divider is 2. So in order to be able to do 450 MHz the UHF oscillator will have to extend to 900 MHZ which is above channel 69.
The dividers are 16, 8, 4 and 2. In order to cover the range 30 to 450 MHz without there been any holes in it the UHF oscillator will need to reach 450 MHz at its lowest setting.
So I have set the range of the UHF oscillator at 450 MHz to 900 MHZ. My example works fine with those limits.
Photos below of some menu positions with it set up for System A 405 lines Channel 2
The number of active lines is per field. The menu is in rough form yet. There is some tweaking to be done.
Frank
30 to 900 MHz in 250 KHz steps vision modulator.
Selectable Positive video modulation AM sound / Negative video modulation FM sound
Selectable 3.5, 4.5, 5.5, 6 and 6.5 MHz sound. 3.5 MHZ is AM only
That will cover most channels. The only one that I can think of that it wont is the French system E. Can anyone think of any others?
I may try doing a special for system E but I am not sure how well it will fit with the available dividers. I haven't done the maths on it yet.
The MC44BS373 data sheet don't explicitly state the UHF frequency range. That is something that I have been caught out with before.
It just says "Channel 21–69 UHF operation" It also says "VHF range possible by internal dividers (30–450 MHz)"
The smallest divider is 2. So in order to be able to do 450 MHz the UHF oscillator will have to extend to 900 MHZ which is above channel 69.
The dividers are 16, 8, 4 and 2. In order to cover the range 30 to 450 MHz without there been any holes in it the UHF oscillator will need to reach 450 MHz at its lowest setting.
So I have set the range of the UHF oscillator at 450 MHz to 900 MHZ. My example works fine with those limits.
Photos below of some menu positions with it set up for System A 405 lines Channel 2
The number of active lines is per field. The menu is in rough form yet. There is some tweaking to be done.
Frank
