525 line NTSC into 405 line converter. - UK Vintage Radio Repair and Restoration Discussion Forum

FERNSEH · 17th Jan 2014, 1:08 pm

Just a fun thing. I connected my 405 line store converter to a NTSC 525 line video recorder to observe what the results would be like.
The 525/60 NTSC system has a line frequency very close to 625/50 system so there was no problem locking up the converter's main clock pulse generator. As the field frequency is 59.94Hz the theoretical line count of the converted picture should be 339. The clock pulse generator is running at 10.195784Mhz so after division of 1000 the 405 line frequency is 10.195794Khz which after dividing by the field rate of 59.94/2 results in a coarse 170 line uninterlaced picture.
There is also a curious 10Hz movement of the raster. Nevertheless the pictures are watchable.

DFWB.

Karen O · 17th Jan 2014, 1:16 pm

Wow! Your converter must be very flexible to cope with that.

My converter would probably lose lock and put out nonesense, and maybe cause the attached TV to catch fire

I'm back to working on my converter again. I just have to synthesise the 405 line frame synch waveforms. There's nothing clever behind this, just carefully cycle counted 'bit banging' code.

FERNSEH · 17th Jan 2014, 1:35 pm

The main clock pulse in this generator in this converter operates at 648 X 15,625HZ = 10.125Mhz. This high frequency is supplied to the address counters for the write function. A different frequency for the read function.
The same 10.125Mhz is first divided by four and then 250 to create the reference for the 405 sync and blanking generator.
There is a mathematical relationship between the two standards: 81/125.
All this is necessary to maintain perfect interlacing of the converter picture.
It's all pretty ancient TTL tech.

DFWB.

Andy Green · 17th Jan 2014, 7:57 pm

Looks like you are doing this on the Ferguson 45T!

FERNSEH · 17th Jan 2014, 9:45 pm

Hi Andy,
The picture was indeed taken from the Ferguson 454T. I tried another set, a 14" GEC and that set was very tolerant of the converted video waveform. No interlace of course.
Line count apart, it is well known that 525/60 and the 625/50 systems are very similar.
The converter processed the NTSC video in same manner as it would with 625 lines.

DFWB.

17th Jan 2014, 1:08 pm	#1
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	525 line NTSC into 405 line converter. Just a fun thing. I connected my 405 line store converter to a NTSC 525 line video recorder to observe what the results would be like. The 525/60 NTSC system has a line frequency very close to 625/50 system so there was no problem locking up the converter's main clock pulse generator. As the field frequency is 59.94Hz the theoretical line count of the converted picture should be 339. The clock pulse generator is running at 10.195784Mhz so after division of 1000 the 405 line frequency is 10.195794Khz which after dividing by the field rate of 59.94/2 results in a coarse 170 line uninterlaced picture. There is also a curious 10Hz movement of the raster. Nevertheless the pictures are watchable. DFWB. Attached Thumbnails

17th Jan 2014, 1:16 pm	#2
Karen O Rest in Peace Join Date: Jul 2011 Location: Bridgnorth, Shropshire, UK. Posts: 787	Re: 525 line NTSC into 405 line converter. Wow! Your converter must be very flexible to cope with that. My converter would probably lose lock and put out nonesense, and maybe cause the attached TV to catch fire I'm back to working on my converter again. I just have to synthesise the 405 line frame synch waveforms. There's nothing clever behind this, just carefully cycle counted 'bit banging' code.

17th Jan 2014, 1:35 pm	#3
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: 525 line NTSC into 405 line converter. The main clock pulse in this generator in this converter operates at 648 X 15,625HZ = 10.125Mhz. This high frequency is supplied to the address counters for the write function. A different frequency for the read function. The same 10.125Mhz is first divided by four and then 250 to create the reference for the 405 sync and blanking generator. There is a mathematical relationship between the two standards: 81/125. All this is necessary to maintain perfect interlacing of the converter picture. It's all pretty ancient TTL tech. DFWB.

17th Jan 2014, 7:57 pm	#4
Andy Green Hexode Join Date: Jan 2005 Location: Waterford, Republic of Ireland Posts: 259	Re: 525 line NTSC into 405 line converter. Looks like you are doing this on the Ferguson 45T!

17th Jan 2014, 9:45 pm	#5
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: 525 line NTSC into 405 line converter. Hi Andy, The picture was indeed taken from the Ferguson 454T. I tried another set, a 14" GEC and that set was very tolerant of the converted video waveform. No interlace of course. Line count apart, it is well known that 525/60 and the 625/50 systems are very similar. The converter processed the NTSC video in same manner as it would with 625 lines. DFWB.