modulators and other standards and converters in general discussed - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

channel405 · 5th Jan 2006, 2:14 am

Hi Darryl,

Thanks for the update. It is reassuring to know that the converter design is progressing well apart form supply issues! I am very much looking forward to the release of this unit, so please keep us posted as to when it makes its debut!

Tim

oldeurope · 5th Jan 2006, 8:57 am

Good morning Darryl,
is the modulator " on board" or is it on a special board?
Maybe it can be made without a modulator. I am interested in 819.
Is it still possible to blow up a 16:9 to 4:3 like in the "big aurora"?
How do you interpolate in 819?

An other important thing, please make it possible to switch off the
modulator. If you add the outputs of different modulators to connect
different sets on one cable, only the modulator that is in use must
be switched on, others off.

BTW the noisy set top box is in smd like all modern mass production
equipment

. It is all a question of a good layout and cirquit.
(My oppinion.) It is not true that smd makes the board smaller.
But this is an other discussion.

Kind regards
Darius

tubesrule · 5th Jan 2006, 3:23 pm

Hello Darius,
The present design has the RF modulator built on the same board with the converter. I wasn't planning on a version without the modulator, but you will be able to disable the modulator on this unit, and it has a line level output, so you could go into one of your modulators for better RF performance.

Unfortunatley the 16:9 blow up feature is one that didn't make it into this unit. It would require more memory to do this, and would increase the cost. Iwas able to get the FLASH memory in, so you will be able to store one image in the unit.

The converter algorithm uses a three line interpolation for all standards. It will also retain the full 720 (actually about 704 active for PAL) pixels for all standards, so the 819 output should be around 7MHz bandwidth.

Switching off the modulator is an important feature for the reasons you've pointed out. I didn't have this at first, but since there will be 4 switches to set the frequency, I just made one position the OFF position, so you are left with 15 possible frequencies which I believe handles all regular RF systems.

Yes, noise can be a real issue. Lots of consumer equipment is not designed or tested to very high specifications. You are absolutely correct that good circuit design and layout are key to a good output. Many times good layout can be a "black art". In fact one of the books I have on the subject of good layout practises is called "A Hand Book of Black Magic".

Darryl

oldeurope · 5th Jan 2006, 9:33 pm

Thanks Darryl,

good evening,
comeing back to the modulator.

The modulator IC's I have seen are quasi parallel sound modulators.
The result is you get two sound carriers, one below and one above the
vision carrier.
The vintage (London) sets and german 441 sets are AM receivers,
they demodulate both sidebands.
As I wrote before, sets like the LV20 ( I think they are called TRF receivers)
do not supress the lower sideband much.
These sets have (two) traps that eleminate the sound carrier above
the vision carrier.
The additional sound carrier below the vision carrier is not suppresed by
these traps and causes a moire.
Did you think about this problem?
I think quasi parallel sound modulators are not a good solution for this
kind of sets.
Except you find one that makes the 90 degree phase shifts... to compensate
the unwanted carrier and supresses it more than 60dB

David Robinson found a very clever way to solve is problem.

All modulators with separate oscillators, the parallel sound modulators,
don't have this problem.
You get best sound and vision if you use an quasi parallel sound or an
intercarrier sound modulator for the intercarrier sets
and an parallel sound modulator for the parallel sound sets.

Kind regards
Darius

tubesrule · 6th Jan 2006, 1:03 am

Darius,
You are correct that all these modulators produce audio carriers above and below the video carrier. No attempt is made in these chips to supress one of the carriers. This will also be true with this converter when outputting FM audio. When outputting AM audio, only the single video and audio carriers will be present (with their associated harmonics). Since the intent of the converter is to support the older, obsolete standards, I doubt there will ever be a need to run in the FM audio mode, but it's there just in case.

Darryl

oldeurope · 6th Jan 2006, 9:14 am

Quote:

Originally Posted by tubesrule

Darius,
You are correct that all these modulators produce audio carriers above and below the video carrier. No attempt is made in these chips to supress one of the carriers. This will also be true with this converter when outputting FM audio. When outputting AM audio, only the single video and audio carriers will be present (with their associated harmonics). Since the intent of the converter is to support the older, obsolete standards, I doubt there will ever be a need to run in the FM audio mode, but it's there just in case.

Darryl

Good morning Darryl,
sorry but I dont agree. In AM and in FM there is a audio carrier above and
below the vision carrier. This has nothing to do with the modulation!
Look at the device overview of the MC44BC373 for example.
The same DSB mixer is used to mix up the modulated (AM or FM) carrier
up with the vision carrier frequency. The two sound carriers and the
RF vision signal are added at the output.
I think in AM the problem is more dramatic because the wanted and the
unwanted (AM) carrier are only 7dBs below peak white (405)

!

Kind regards
Darius

tubesrule · 6th Jan 2006, 6:37 pm

Hi Darius,
I think I didn't explain myself very well. What I meant is I am using the internal audio modulator when I need FM audio. This results in the two carriers. For AM audio I am running two independent modulators like Steve McVoy and David Robinson did in their designs. This was also necessary to achieve the 11.25MHz spacing for System E. With System A it was possible to pull the internal audio modulator by feeding an appropriate reference into the chip, but you need to pull it almost 2:1 for System E, and this was not possible. The second modulator was also required for early System M which was negative video and AM audio which is not possibly with these chips.

Darryl

oldeurope · 6th Jan 2006, 7:21 pm

Ah, thanks I understand. It is the same in my modulator of course;
This system is called parallel sound and is a fundamental thing.

It was definatly David Robinsons idea to switch off the sound carrier
in the quasi parallel sound IC's and use the vision input of one IC for
sound. I just wanted to point that out.

Kind regards,
Darius

tubesrule · 6th Jan 2006, 9:27 pm

Actually this is a fairly common thing to do. On my first modulator years ago I used two of those little japanesse metal cage packaged modulators and just opened them up and defeated the audio carrier, then used the video portion of each, one for the video and one for the audio. I still use that modulator to this day. This is also what Steve did on his design a few years back only with two MC1374 chips. He didn't use the audio modulator in the chips, and just used the video portion, one for video, and one for audio by biasing the video input to set the carrier level.

Darryl

oldeurope · 7th Jan 2006, 9:41 am

Good morning Darryl,
this system has two disadvantages.
First the (Motorola) IC can not generate 100% modulation deepth,
this makes the signal non authentic and you get noise from
two PLL ICs.

This is a problem in all these "all in one ICs".
As I wrote before, some sets catches noise out of the channel.
This makes it difficult.

Kind regards
Darius

FERNSEH · 7th Jan 2006, 10:51 pm

Good evening Gentlemen,
In the near future I will acquire a good number of French 819 line TV receivers. In order that I can use the sets a special Band 3 modulator for system E will have to be constructed. A design exists on a French website. The Aurora standards converter will provide the video from a 625 line source. The sound is AM.

DFWB

FERNSEH · 7th Jan 2006, 11:13 pm

The design for the system E modulator can be found on:

http://perso.wanadoo.fr/tsf/tv/modul.htm

The website has vintage radio as well as TV

DFWB

oldeurope · 8th Jan 2006, 11:29 am

Quote:

Originally Posted by FERNSEH

The design for the system E modulator can be found on:

http://perso.wanadoo.fr/tsf/tv/modul.htm

The website has vintage radio as well as TV

DFWB

Good morning Fernseh,

I had a quick look on the schematic at your link.

The vision input is not 75 Ohms terminated,
the temperature compensation is wrong,
The DC restorer in slow acting and you don't need one because
the aurora has sync tips on the zero line.
Modulating the oscillator causes AM and FM.

There is no difference in a system A and E because they both have
pos vision AM and AM sound.

I would prefer this one.
I use it in my 405 standard converter modulators with success.

Kind regards
Darius

oldeurope · 8th Jan 2006, 5:59 pm

Quote:

Originally Posted by Darius

Good morning Fernseh,

I had a quick look on the schematic at your link.

The vision input is not 75 Ohms terminated,
...

Kind regards
Darius

Sorry it is, but not for DC. With emitterfollower outputs
this input can cause trouble with the sync. It is cut sometimes.
OP amps don't like it too.
Remember the problems with DIN AV inputs like this

A good video input is terminated with a 75 Ohms resistor.

Look at the screenshot from the oscilloscope at point B.
The "DC restorer" is very bad the sync tip level changes over the picture.

I think the Domino has synctips on zero too. This makes the modulator
very easy if you want to build one for an other channel.

Kind regards
Darius

ppppenguin · 8th Jan 2006, 6:09 pm

I agree with Darius here. A video input should normally have a 75R resistor directly across the input.

There are other unusual (but satisfactory) input arrangments such as a 75R series resistor feeding the emitter of a grounded base amplifier.

5th Jan 2006, 2:14 am	#21
channel405 Tetrode Join Date: Jun 2004 Location: CH3, Blaen Plwyf Transmitter, Aberystwyth, WALES Posts: 72	Re: modulators and other standards and converters in generell discussed Hi Darryl, Thanks for the update. It is reassuring to know that the converter design is progressing well apart form supply issues! I am very much looking forward to the release of this unit, so please keep us posted as to when it makes its debut! Tim

5th Jan 2006, 8:57 am	#22
oldeurope Retired Dormant Member Join Date: Dec 2003 Location: Solingen, Germany Posts: 727	Re: modulators and other standards and converters in generell discussed Good morning Darryl, is the modulator " on board" or is it on a special board? Maybe it can be made without a modulator. I am interested in 819. Is it still possible to blow up a 16:9 to 4:3 like in the "big aurora"? How do you interpolate in 819? An other important thing, please make it possible to switch off the modulator. If you add the outputs of different modulators to connect different sets on one cable, only the modulator that is in use must be switched on, others off. BTW the noisy set top box is in smd like all modern mass production equipment. It is all a question of a good layout and cirquit. (My oppinion.) It is not true that smd makes the board smaller. But this is an other discussion. Kind regards Darius

5th Jan 2006, 3:23 pm	#23
tubesrule Hexode Join Date: Jul 2004 Location: Michigan USA Posts: 325	Re: modulators and other standards and converters in generell discussed Hello Darius, The present design has the RF modulator built on the same board with the converter. I wasn't planning on a version without the modulator, but you will be able to disable the modulator on this unit, and it has a line level output, so you could go into one of your modulators for better RF performance. Unfortunatley the 16:9 blow up feature is one that didn't make it into this unit. It would require more memory to do this, and would increase the cost. Iwas able to get the FLASH memory in, so you will be able to store one image in the unit. The converter algorithm uses a three line interpolation for all standards. It will also retain the full 720 (actually about 704 active for PAL) pixels for all standards, so the 819 output should be around 7MHz bandwidth. Switching off the modulator is an important feature for the reasons you've pointed out. I didn't have this at first, but since there will be 4 switches to set the frequency, I just made one position the OFF position, so you are left with 15 possible frequencies which I believe handles all regular RF systems. Yes, noise can be a real issue. Lots of consumer equipment is not designed or tested to very high specifications. You are absolutely correct that good circuit design and layout are key to a good output. Many times good layout can be a "black art". In fact one of the books I have on the subject of good layout practises is called "A Hand Book of Black Magic". Darryl

5th Jan 2006, 9:33 pm	#24
oldeurope Retired Dormant Member Join Date: Dec 2003 Location: Solingen, Germany Posts: 727	Re: modulators and other standards and converters in generell discussed Thanks Darryl, good evening, comeing back to the modulator. The modulator IC's I have seen are quasi parallel sound modulators. The result is you get two sound carriers, one below and one above the vision carrier. The vintage (London) sets and german 441 sets are AM receivers, they demodulate both sidebands. As I wrote before, sets like the LV20 ( I think they are called TRF receivers) do not supress the lower sideband much. These sets have (two) traps that eleminate the sound carrier above the vision carrier. The additional sound carrier below the vision carrier is not suppresed by these traps and causes a moire. Did you think about this problem? I think quasi parallel sound modulators are not a good solution for this kind of sets. Except you find one that makes the 90 degree phase shifts... to compensate the unwanted carrier and supresses it more than 60dB David Robinson found a very clever way to solve is problem. All modulators with separate oscillators, the parallel sound modulators, don't have this problem. You get best sound and vision if you use an quasi parallel sound or an intercarrier sound modulator for the intercarrier sets and an parallel sound modulator for the parallel sound sets. Kind regards Darius

6th Jan 2006, 1:03 am	#25
tubesrule Hexode Join Date: Jul 2004 Location: Michigan USA Posts: 325	Re: modulators and other standards and converters in generell discussed Darius, You are correct that all these modulators produce audio carriers above and below the video carrier. No attempt is made in these chips to supress one of the carriers. This will also be true with this converter when outputting FM audio. When outputting AM audio, only the single video and audio carriers will be present (with their associated harmonics). Since the intent of the converter is to support the older, obsolete standards, I doubt there will ever be a need to run in the FM audio mode, but it's there just in case. Darryl

6th Jan 2006, 6:37 pm	#27
tubesrule Hexode Join Date: Jul 2004 Location: Michigan USA Posts: 325	Re: modulators and other standards and converters in generell discussed Hi Darius, I think I didn't explain myself very well. What I meant is I am using the internal audio modulator when I need FM audio. This results in the two carriers. For AM audio I am running two independent modulators like Steve McVoy and David Robinson did in their designs. This was also necessary to achieve the 11.25MHz spacing for System E. With System A it was possible to pull the internal audio modulator by feeding an appropriate reference into the chip, but you need to pull it almost 2:1 for System E, and this was not possible. The second modulator was also required for early System M which was negative video and AM audio which is not possibly with these chips. Darryl

6th Jan 2006, 7:21 pm	#28
oldeurope Retired Dormant Member Join Date: Dec 2003 Location: Solingen, Germany Posts: 727	Re: modulators and other standards and converters in generell discussed Ah, thanks I understand. It is the same in my modulator of course; This system is called parallel sound and is a fundamental thing. It was definatly David Robinsons idea to switch off the sound carrier in the quasi parallel sound IC's and use the vision input of one IC for sound. I just wanted to point that out. Kind regards, Darius

6th Jan 2006, 9:27 pm	#29
tubesrule Hexode Join Date: Jul 2004 Location: Michigan USA Posts: 325	Re: modulators and other standards and converters in generell discussed Actually this is a fairly common thing to do. On my first modulator years ago I used two of those little japanesse metal cage packaged modulators and just opened them up and defeated the audio carrier, then used the video portion of each, one for the video and one for the audio. I still use that modulator to this day. This is also what Steve did on his design a few years back only with two MC1374 chips. He didn't use the audio modulator in the chips, and just used the video portion, one for video, and one for audio by biasing the video input to set the carrier level. Darryl

7th Jan 2006, 9:41 am	#30
oldeurope Retired Dormant Member Join Date: Dec 2003 Location: Solingen, Germany Posts: 727	Re: modulators and other standards and converters in generell discussed Good morning Darryl, this system has two disadvantages. First the (Motorola) IC can not generate 100% modulation deepth, this makes the signal non authentic and you get noise from two PLL ICs. This is a problem in all these "all in one ICs". As I wrote before, some sets catches noise out of the channel. This makes it difficult. Kind regards Darius

7th Jan 2006, 10:51 pm	#31
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: modulators and other standards and converters in generell discussed Good evening Gentlemen, In the near future I will acquire a good number of French 819 line TV receivers. In order that I can use the sets a special Band 3 modulator for system E will have to be constructed. A design exists on a French website. The Aurora standards converter will provide the video from a 625 line source. The sound is AM. DFWB

7th Jan 2006, 11:13 pm	#32
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: modulators and other standards and converters in generell discussed The design for the system E modulator can be found on: http://perso.wanadoo.fr/tsf/tv/modul.htm The website has vintage radio as well as TV DFWB

8th Jan 2006, 6:09 pm	#35
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: modulators and other standards and converters in generell discussed I agree with Darius here. A video input should normally have a 75R resistor directly across the input. There are other unusual (but satisfactory) input arrangments such as a 75R series resistor feeding the emitter of a grounded base amplifier.