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75 ohm vs 50 ohm cables
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nomadII



Joined: 16 Jun 2006
Posts: 252



PostLink    Posted: Fri Jan 11, 2008 8:20 am    Post subject: Reply with quote


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Dave,

Settle down before your wife bans you from the forum again. Use your post wisely!!

How & why would anyone argue about this? Is C.W. McCall your next door neighbor?

My guess is that it would cost me more to find 50ohm cables than 75?
-------------------------------------------------------------------------------------------------

Ah the 50 Ohm coax.

First use: Los Alamos, New Mexico
Trinity Project

It was the only thing they could find that would transmit data prior to destruction due to a very inhospitable climate.

Note: Back in the day it was Fast!!!
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chillman



Joined: 09 Apr 2007
Posts: 134
Location: Germany, Bavaria


PostLink    Posted: Sun Jan 13, 2008 1:59 pm    Post subject: Reply with quote

Can anyone tell me what type of coax-cable can be used for video? Can I use RG-59? Thanks!
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Joust



Joined: 05 May 2006
Posts: 2430
Location: Almonte, Ontario, Canada

TV/Projector: Marquee 8501LC


PostLink    Posted: Sun Jan 13, 2008 3:21 pm    Post subject: Reply with quote

Yes but be careful, RG58 is 50ohm. RG59 is 75 most commonly used in Cable TV installations.
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chillman



Joined: 09 Apr 2007
Posts: 134
Location: Germany, Bavaria


PostLink    Posted: Sun Jan 13, 2008 3:33 pm    Post subject: Reply with quote

So it doesn't really matter which cable I use as long as it's 75 Ohm? I want to make a RGBHV cable for my projector. RG59 is quite cheap, (20$ for 100m) so I wonder if it's good enough for a 10m connection to my Projector.
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Joust



Joined: 05 May 2006
Posts: 2430
Location: Almonte, Ontario, Canada

TV/Projector: Marquee 8501LC


PostLink    Posted: Sun Jan 13, 2008 3:45 pm    Post subject: Reply with quote

At that price, try it and see.
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jkruger



Joined: 24 Oct 2007
Posts: 2435
Location: Carlsbad, CA


PostLink    Posted: Sun Jan 13, 2008 4:16 pm    Post subject: Reply with quote

I'm no EE but I have never seen any difference between 50 and 75 ohm cable in the 30 yrs I have been messing with this stuff, except for one application, a scanner antenna. I tried to go with the cable I had (75 ohm) when I put up my first big scanner antenna and it was obvious that I wasn't getting nearly the signal strength I should have been. I switched to RG-213 (much bigger conductor and better shielding) and the difference was amazing. I started pulling in low power transmissions from literally hundreds of miles away instead of ten. It's the best I have ever used. RG-11 is supposed to be better. Too big for hooking up video stuff though.

Last edited by jkruger on Sun Jan 13, 2008 4:26 pm; edited 1 time in total
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ecrabb
Forum Moderator


Joined: 13 Mar 2006
Posts: 15909
Location: Utah

TV/Projector: JVC RS40, Epson 5010


PostLink    Posted: Sun Jan 13, 2008 4:26 pm    Post subject: Reply with quote

chillman wrote:
So it doesn't really matter which cable I use as long as it's 75 Ohm? I want to make a RGBHV cable for my projector. RG59 is quite cheap, (20$ for 100m) so I wonder if it's good enough for a 10m connection to my Projector.

For that distance, I'd use RG-6. The price difference shouldn't be that significant for the 100m spool you'll need. By far, the most expensive part will be the BNC connectors... $x * 10.

I was going to build my own cable, but the BNC connectors (or the tools to crimp them if you go that route) get pricey enough that a pre-made cable made plenty of sense - it was way cheaper. I bought one of these just to try and it works beautifully:
https://homenetworksupply.com/products_details.aspx?theme_id=1454900095&department_id=4629350247&sub_id=5457350208&product_id=3735708845



It was cheap enough, I couldn't even buy the BNC connectors for that price. I'm not pushing 1080p into a 9"-er, though, so I wouldn't know if they weren't excellent.

SC
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Joust



Joined: 05 May 2006
Posts: 2430
Location: Almonte, Ontario, Canada

TV/Projector: Marquee 8501LC


PostLink    Posted: Sun Jan 13, 2008 4:39 pm    Post subject: Reply with quote

Ah yes, this is exactly the point made earlier.
Radio uses much higher frequencies and MUCH MUCH lower signal levels.
therefor with Radio you WILL see a huge difference, but with direct connected sources at video frequencies, you should see nothing.
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chillman



Joined: 09 Apr 2007
Posts: 134
Location: Germany, Bavaria


PostLink    Posted: Sun Jan 13, 2008 10:21 pm    Post subject: Reply with quote

ecrabb wrote:
It was cheap enough, I couldn't even buy the BNC connectors for that price.

I know that it doesn't make too much sense if you do this because of the price, but I can't see how the BNC connectors should make a self-made cable that expensive. They cost from 30 (european) ct. for a crimp version to 50 ct. for a solder version each, so 5 for the connectors for one cable + ~10 for the 5x10m cable is 15 for a 10m RGBHV cable. This would be quite cheap if it would provide a good connection.
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Spanky Ham



Joined: 22 Mar 2006
Posts: 5634
Location: Comedy Central


PostLink    Posted: Mon Jan 14, 2008 5:17 am    Post subject: Reply with quote

Chill,
It depends on how many cables you are making for it to be worthwhile. You can get a good quality tool for under $100. The connectors I think are around $2.
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ecrabb
Forum Moderator


Joined: 13 Mar 2006
Posts: 15909
Location: Utah

TV/Projector: JVC RS40, Epson 5010


PostLink    Posted: Mon Jan 14, 2008 5:28 am    Post subject: Reply with quote

The connectors I was thinking of were like $10/ea. and I was looking at $50 worth of Belden RG-6 snake. So, you'd have $100 in connectors, a $100 crimp tool, plus the $50 worth of cable... and the time of getting it all and putting it together. I decided $250 was a little steep and I had too much other stuff to do. Now, with more of my racking going HDMI, I'm even more glad I didn't build it myself.

But, with $2 connectors, cheaper RG-6, and a less expensive tool... It's not a bad idea at all. Go for it!

SC
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