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How much does cable length matter?

 
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Kilian




Joined: 06 Dec 2020
Posts: 3



PostLink    Posted: Sun Oct 03, 2021 10:49 am    Post subject: How much does cable length matter? Reply with quote


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Hello everyone,
i am using a Sony vph 1272qm with a 15m extron cable and i am wondering if using a shorter cable (>1m) can improve the picture. I am using a ps3 with a 1:1 copy made by conrad electronics of the hdfury 2 and 1080i. Thank you
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kal
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Joined: 06 Mar 2006
Posts: 17850
Location: Ottawa, Canada

TV/Projector: JVC DLA-NZ7


PostLink    Posted: Sun Oct 03, 2021 12:17 pm    Post subject: Reply with quote

I'm assuming the 15m cable is an HDMI (digital) cable. For best image quality use a long HDMI (digital) cable and short analog cable between your HDMI to RGB converter and the projector.

Ideal picture quality would be to use no analog cable at all and use an HDMI card in the projector that is made specifically for your projector: http://www.curtpalme.com/IFB-FULLHD.shtm

It also has extra features that'll improve image quality like gamma boost (an absolute requirement for CRT projectors if you can't control it in the source).

Cheers and welcome to the forum!

Kal

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Kilian




Joined: 06 Dec 2020
Posts: 3



PostLink    Posted: Sun Oct 03, 2021 12:43 pm    Post subject: Reply with quote

The 15m cable is a vga to rgbhv cable, is it possible that a 1272 is good enough that i could tell the difference to a shorter cable?
Sadly a hdmi card is too expensive for me but i have no gamma adjustment in my video chain, would it be possible that someone could share the circuit design of the box1040 or any other gamma boost cuircuit?
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kal
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Joined: 06 Mar 2006
Posts: 17850
Location: Ottawa, Canada

TV/Projector: JVC DLA-NZ7


PostLink    Posted: Sun Oct 03, 2021 1:02 pm    Post subject: Reply with quote

Kilian wrote:
The 15m cable is a vga to rgbhv cable, is it possible that a 1272 is good enough that i could tell the difference to a shorter cable?

There's no black and white answer here. That would depend on the quality of the 2 cables, how well the 1272 is set up, and whether you notice the difference too.

The bigger question is: If you can actually use a shorter cable like less than 1 meter as you mentioned, why are you using a 15 meter cable?

Quote:
would it be possible that someone could share the circuit design of the box1040 or any other gamma boost cuircuit?

That's not something I have or can provide. Sorry!

Kal

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AnalogRocks
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Joined: 08 Mar 2006
Posts: 26690
Location: Toronto, Ontario, Canada

TV/Projector: Sony 1252Q, AMPRO 4000G


PostLink    Posted: Wed Oct 06, 2021 4:40 pm    Post subject: Reply with quote

Kilian wrote:
The 15m cable is a vga to rgbhv cable, is it possible that a 1272 is good enough that i could tell the difference to a shorter cable?
Sadly a hdmi card is too expensive for me but i have no gamma adjustment in my video chain, would it be possible that someone could share the circuit design of the box1040 or any other gamma boost cuircuit?



http://www.curtpalme.com/forum/viewtopic.php?t=8540&postdays=0&postorder=asc&&start=0

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kal
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TV/Projector: JVC DLA-NZ7


PostLink    Posted: Wed Oct 06, 2021 4:47 pm    Post subject: Reply with quote

Good find Jeremy!

Kal

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AnalogRocks
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Joined: 08 Mar 2006
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Location: Toronto, Ontario, Canada

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PostLink    Posted: Wed Oct 06, 2021 5:02 pm    Post subject: Reply with quote

Looks like my memory is getting better Wink
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Tim in Phoenix




Joined: 21 Oct 2006
Posts: 4378
Location: Phoenix


PostLink    Posted: Thu Oct 07, 2021 12:09 pm    Post subject: Reply with quote

Guys

Analog cables impose capacitance and resistance on the signal. Capacitance will erode bandwidth and fine detail may be reduced. Resistance will lower the signal voltage slightly, so, Yes, a shorter cable is helpful.
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gjaky




Joined: 05 Jun 2010
Posts: 2789
Location: Budapest, Hungary


PostLink    Posted: Sun Oct 10, 2021 8:47 pm    Post subject: Reply with quote

AnalogRocks wrote:
Kilian wrote:
The 15m cable is a vga to rgbhv cable, is it possible that a 1272 is good enough that i could tell the difference to a shorter cable?
Sadly a hdmi card is too expensive for me but i have no gamma adjustment in my video chain, would it be possible that someone could share the circuit design of the box1040 or any other gamma boost cuircuit?



http://www.curtpalme.com/forum/viewtopic.php?t=8540&postdays=0&postorder=asc&&start=0


The proposed circuit while works reasonably well with static test patterns, have difficulties with bandwidth consistency -it works differently when high bandwidth is involved, and real video content for sure contain mixed signals bandwidth-wise. Also a downside is that the characteristic is fixed

A more correct solution is to use analog multipliers and multiply the signal with themselves, in this way the rate can be adjusted continuously, the downside is cost in components.

Quote:
Analog cables impose capacitance and resistance on the signal. Capacitance will erode bandwidth and fine detail may be reduced. Resistance will lower the signal voltage slightly, so, Yes, a shorter cable is helpful.


This is a very vague and imprecise explanation. Video systems use fully-terminated cables, where there is no such thing as cable capacitance or resistance, only impedance. The bandwidth is not eroded by the simply capacitance, because the cable capacitance always comes with series inductance (the two what gives in fact the characteristic impedance of a cable), and by effect cancel eachother out, making the cable frequency independent -in theory!
The loss of bandwidth mainly comes from the non ideality factors of the cables like 'skin effect' of conductors, or dielectric loss of the insulating material of the cable, etc.

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Kilian




Joined: 06 Dec 2020
Posts: 3



PostLink    Posted: Tue Nov 30, 2021 8:07 pm    Post subject: Reply with quote

Thank you very much for your advice. After finally having a good spacer setup i will now get shorter cables and build the gamma box.
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AnalogRocks
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Joined: 08 Mar 2006
Posts: 26690
Location: Toronto, Ontario, Canada

TV/Projector: Sony 1252Q, AMPRO 4000G


PostLink    Posted: Fri Dec 03, 2021 7:12 am    Post subject: Reply with quote

AS a guy that has been swapping cables for 35 years or so. Cable can make or break a setup.
Also I've seen people swapping all sorts of equipment without changing cables an not being able to figure out why the problem persists. I had a tech here swapping cable modems back in the day c.1999 and he killed 2 modems before realizing a)he sound have listened to me and tested the power supply first ( 12 volts tested 18 volts and the 5 volts tested 9 volts ) and b) change the cable run from the wall to the modem to get a reliable signal.

I have also swapped high end audio cables ( which I picked up surplus ) and found there IS a difference in sound. I ended up using a certain cable for the subwoofer because it sounded better with bass, a different cable for the center channel because that cable sounded better with dialog. On the front channels I found there were two cables that fit the bill. One set sounded amazing in stereo, say playing a tape or a record, but the other cables sounded better on sound effects in movies for the 5.1 sound.

On the video side I have swapped 5 or 6 cables in a setup and found some have ringing ( blurry or double edges particularly on the sides of the frame )
Some were spot on! Great picture and yes with analog cables you want the shortest run possible OR the best cable out of the bunch, even if one is longer than optimal.

On the digital HDMI hell side. sometimes you try a short cable like a 3 foot because it fits the situation and it just won't work reliably. Then you have to go 6 foot or 10 foot to get a stable digital link, because of the digital timings inside the cable. Kal ran into this as i recall.

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virusc




Joined: 11 Apr 2007
Posts: 318
Location: Massachusetts


PostLink    Posted: Wed Jun 29, 2022 12:22 pm    Post subject: Reply with quote

I can tell you this. I have a Barco Cine7 which is not that good of a projector but it was well setup. I had a Vidikron 25' 5ch BNC cable snake that I was told was sold for over $1000 to customers that I compared to a 5 ch Monster s1000 BNC snake that was only 9' long. The difference was night and day and the Vidikron was dimmer and had halo ringing. I was very surprised as the longer Vidikron looked that much worse. I think it is worth testing BNC cables as they are so cheap to get some used from the past to see.
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