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57 posts

Master Geek


# 41361 14-Sep-2009 18:24
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Now some of you guys might be able to help here. What I am trying to do is Run 2 TVs in a Camp Ground Building. They are fed from a DVD player with 2 AV outputs. (thats with the yellow plug). The DVD player is a unit designed for automotive and we are running it with a power supply. I have used RG 50 0hmn cable from Dick smith, its smaller in size than what is used for RF TV... and we dont think the signal is getting down the line properly. One lead is about 7 metres and one is about 10metres. The signal we get at the other end of the cable is very Blurry, it has good colour, but with a blue tint. I think Ive done something wrong but Im not sure what. The TVs are New 30 inch LCD from the warehouse,,  I have run previosly AV leads from FTA box to 2 TVs in my motorhome and it seems OK.

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  # 255698 14-Sep-2009 19:01
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TV cables for video and aerial are all 75 Ohms not 50 Ohms. This is more than likely the cause of your problems.







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Master Geek


  # 255915 15-Sep-2009 17:33
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Thanks, I dont know how I made that mistake , I should have known. I brought RG58C/U 50 ohmn, because it was light and flexible and easy to solder on RCA plugs. So I am going to change this, the Idea is good we have a DVD that plays and repeats, and screens on the TVs.. So let me get this straight I did know that RF signal would have needed 75 ohmn, I wouldnt of got that wrong,, but I never thought about what to use on AV leads with RCA plugs, so this should always be 75 ohmn also.

 
 
 
 


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  # 255986 16-Sep-2009 01:00
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Yes, look for CCTV cable, as the 75ohm RF stuff is useless at baseband frequencies because of its steal core.

But even over those distances on wrong cable you should be ok. Are the tvs fine when directly connected to the dvd player on the same input?




Richard rich.ms



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Master Geek


  # 256007 16-Sep-2009 08:26
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Yes they are fine when coupled direct with a short lead.

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  # 256038 16-Sep-2009 10:12
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richms: Yes, look for CCTV cable, as the 75ohm RF stuff is useless at baseband frequencies because of its steal core.


Thanks richms, this actually address's something I'm about to look into myself.  I'm looking at putting some cameras outside and feeding them into the AV inputs on two TV's around the house.  So camera into AV splitter (and possibly distribution amp) and then into AV1/AV2 inputs of each TV.

Could you describe the best cable to use for this (and possibly provide a web link example).  I was going to use RG59 coax for this as I've heard this was the best choice for running component video signals up to a projector etc.  (59 apparently better than 6 for this application).  Crimp/compression rca fittings direct onto this cable.

How's this plan?  Or should I be looking at another type of cable for composite/yellow RCA video signal distribution?
Cheers.



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Master Geek


  # 256094 16-Sep-2009 12:39
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petermcg here
I found out also that RG59 is the cable to use. I and going to terminate the ends with crimp on F connector and adapt back to RCA. Interestingly enough I discovered that the RCA plugs although they are used all the time are not rated at 75 ohmn but they are 50 ohmn I think.
Also I use an rg59 cable that is figure 8 style and has 12 volts feed on the side of the coax for cctv,, It works well over long distance and I feed it into a DVR card in a $30 computer

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  # 256205 16-Sep-2009 16:42
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RCA plugs have no specific impedance. BNC's do, F's - well its just fortunate luck if they operate near a specific one, particually with the mess that is the sleeve that the pin slips into - but its more then good enough.

baseband video is below 10MHz (More if its HD), RF starts at 50MHz - since there is the skin effect at higher frequencies they make the center of RF coax of steel since its cheaper and stronger so works ok with F connectors. Whereas solid copper will usually just bend rather then go into an F socket.

There are cables by belden that are actually called CCTV RG6 that is solid copper, but putting an F on it is a bit of a hit and miss affair when it comes to putting the RCA adapert onto it. IMO stick with BNC and then adapt that or just solder a RCA on, the CCTV stuff I got had a copper screen as well so was solderable.




Richard rich.ms

 
 
 
 


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  # 256390 17-Sep-2009 09:38
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Cheers Richms,

So basically, RG59 for any video signals, such as composite/yellow rca, component video.
RG6 for aerial/satellite connections.

Given the RG6 foil shielding protects frequencies over 50Mhz, would this suggest RG59 would be the best chioce for audio interconnects, such as sub woofer cables etc? RG6 gives a nice solid core for the signal, but essentially no sheilding in the frequencies of the analogue audio signals.

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  # 256403 17-Sep-2009 10:17
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RG6 gives a useless core for baseband signals unless you seek out the CCTV stuff, the shield is there but you cant solder to it. lower frequencies are ok with a much looser braid then RF stuff.

There are RF only RG59 cables, so just watch what you get. IMO if it is targeted at the security camera market then you are good to go...




Richard rich.ms

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