I've seen a number of ways of doing this.

* Small capacitor from C to Y. Around 470 pF seems to be popular and works
relatively well. But there seems to be excessive color noise compared
to using the composite output of the same source (which presumably had to
do the same conversion). Increasing the cap value decreases color noise
but smears the picture.

* Direct connection from C to Y. Apparently, some cheap cables do this
(based on an ohmmeter, unless there is something else in there that
doesn't show up as a cap or resistor!). Works well on some sources
with decent resolution and minimal color noise, won't even sync on others.

* Rs in addition to the cap, but reduces video level.

* Active approaches?

So, is there an optimal conversion scheme???

Thanks.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
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On Nov 5, 11:23 am, Sam Goldwasser wrote:
I've seen a number of ways of doing this.

* Small capacitor from C to Y. Around 470 pF seems to be popular and works
relatively well. But there seems to be excessive color noise compared
to using the composite output of the same source (which presumably had to
do the same conversion). Increasing the cap value decreases color noise
but smears the picture.

* Direct connection from C to Y. Apparently, some cheap cables do this
(based on an ohmmeter, unless there is something else in there that
doesn't show up as a cap or resistor!). Works well on some sources
with decent resolution and minimal color noise, won't even sync on others.

* Rs in addition to the cap, but reduces video level.

* Active approaches?

So, is there an optimal conversion scheme???

Thanks.

--- sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
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Truly no need for any active circuitry. The Bosch encoder from the mid
'80s used passive mixing and was a broadcast product. Capacitor
technique preferred.

GG

I did some more experiments using the composite and S-video outputs of
a Cyberhome CH-DVD 300S DVD player feeding an RCA ColorTrak 2000 (circa
1984) TV as well as a small LCD monitor.

Best (lowest color noise): Composite output.

Next best: Direct Y to C connection using $3 eBay S-video adapter. (Virtually
the same with home-built adapter that wasn't well shielded.)

Worst (highest color noise): 470 pF between Y and C.

The B/W resolution seemed similar for all three. There was almost no color
noise with the composite output. The color noise shows up at edges and
especially with lettering like titles and credits, or where there is fine
detail.

Comments?

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

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On Nov 7, 9:49 am, Sam Goldwasser wrote:
I did some more experiments using the composite and S-video outputs of
a Cyberhome CH-DVD 300S DVD player feeding an RCA ColorTrak 2000 (circa
1984) TV as well as a small LCD monitor.

Best (lowest color noise): Composite output.

Next best: Direct Y to C connection using $3 eBay S-video adapter. (Virtually
the same with home-built adapter that wasn't well shielded.)

Worst (highest color noise): 470 pF between Y and C.

The B/W resolution seemed similar for all three. There was almost no color
noise with the composite output. The color noise shows up at edges and
especially with lettering like titles and credits, or where there is fine
detail.

Comments?

--- sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

I thought about that more after I said capacitors. The ideal situation
would be to use a summing amplifier. Nearly as good would be
converting the chroma to current output rather than voltage using a
transconductance amplifier and then resistively sum the chroma and
luma. What exactly was in the home built combiner? Just a 'Y' cord?

None of that touches digital. HD across the LAN cables works great
with the 'TV' computer connected DVI to a 50" DLP.

GG

writes:

On Nov 7, 9:49 am, Sam Goldwasser wrote:
I did some more experiments using the composite and S-video outputs of
a Cyberhome CH-DVD 300S DVD player feeding an RCA ColorTrak 2000 (circa
1984) TV as well as a small LCD monitor.

Best (lowest color noise): Composite output.

Next best: Direct Y to C connection using $3 eBay S-video adapter. (Virtually
the same with home-built adapter that wasn't well shielded.)

Worst (highest color noise): 470 pF between Y and C.

The B/W resolution seemed similar for all three. There was almost no color
noise with the composite output. The color noise shows up at edges and
especially with lettering like titles and credits, or where there is fine
detail.

Comments?

--- sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

I thought about that more after I said capacitors. The ideal situation
would be to use a summing amplifier. Nearly as good would be
converting the chroma to current output rather than voltage using a
transconductance amplifier and then resistively sum the chroma and
luma. What exactly was in the home built combiner? Just a 'Y' cord?

I've done the home-built with the capacitor, as well as with Y and C
shorted together, or with a small resistor between them.

The IC solution like Intersel ISL59114 has the summing amp approach
along with a low pass filter on both Y and C. I wonder
if the LPF is part of the missing link here. Except that the commercial
S-video adapter has nothing inside as far as I can tell.

None of that touches digital. HD across the LAN cables works great
with the 'TV' computer connected DVI to a 50" DLP.

Let met get into S-video before jumping into digital.

Thanks!

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
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On Nov 7, 5:13 pm, Sam Goldwasser wrote:
writes:
snip
I thought about that more after I said capacitors. The ideal
situation
would be to use a summing amplifier. Nearly as good would be
converting the chroma to current output rather than voltage using
a
transconductance amplifier and then resistively sum the chroma
and
luma. What exactly was in the home built combiner? Just a 'Y'
cord?

I've done the home-built with the capacitor, as well as with Y and
C
shorted together, or with a small resistor between them.

The IC solution like Intersel ISL59114 has the summing amp approach
along with a low pass filter on both Y and C. I wonder
if the LPF is part of the missing link here. Except that the
commercial
S-video adapter has nothing inside as far as I can tell.

None of that touches digital. HD across the LAN cables works
great
with the 'TV' computer connected DVI to a 50" DLP.

Let met get into S-video before jumping into digital.

Thanks!

--- sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/

The filtering is done in the Y/R-Y/B-Y section before modulating the
subcarrier so it's just fine to sum it together.

GG