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Joined: May 2003
Posts: 74
J
jkraft Offline OP
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Originally Posted by cableguy619
As a cable technician, I recommend/request the following: DO NOT PUT THE SPLITTER IN THE ATTIC!!!!!!!!!! Run the new line back to the existing splitter, and either use an unused port on that splitter, or add another splitter to the existing one.


Sorry, I'll try and do that next time, job's already drywalled and can't fish down now.

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Joined: May 2003
Posts: 1,158
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Joined: Dec 2003
Posts: 886
H
Member
Wow! A little off topic but I just saw this in that last link. About time they came out with something like this. http://www.hollandelectronics.com/catalog/catalog.php?product_id=Dark-Meter-System

I would recommend it to all of you guys who install coax. No need to wait for the cable or sat company to provide service and uncover your mistakes. Check each cable run or an entire system and know that your work is good before the house is sold.

-Hal

Joined: Aug 2001
Posts: 7,520
P
Member
I know most people reading the thread are probably aware of this, but just in case anyone isn't.....

When it comes to clipping center and shield together to trace a cable with an ohmmeter or other simple continuity tester, remember that cables which run to an antenna may show a DC short under normal conditions anyway. A folded dipole on a regular Yagi array, for example, will do so. It might look like a dead short to DC, but it isn't at RF!

And a little off-topic I know, but when it comes to simple DC continuity tests, I wonder how many other U.K. readers still have one of the old dark green Hosiden Besson "Bleeptest" units, as were standard GPO issue for many years?



Joined: Dec 2003
Posts: 886
H
Member
On that note keep in mind that most splitter ports are a dead short to DC. Also a staple through a cable is going to be a short also.

The OP asked about an easy way to identify the feed when cutting a cable to insert a splitter. Many times it is difficult to determine where the other end of a cable is so it is not always possible to disconnect the far end to put a tester on it or even know what it is connected to. The only way to handle this is to look for the end with signal on it then you know it's the feed. Only way to do that is with a signal level meter or a TV. There is no cheap tester that will tell you if you have signal.

-Hal

Joined: Mar 2005
Posts: 1,213
S
Member
You could take a small portable TV with you, and touch the antenna to the center conductor. The active one should provide a nice strong signal on any VHF channel when you contact it.

I'm sad my little 1.5" LCD TV will be worthless come next year when all broadcast goes HD frown On the bright side, HDTV is awesome...

Joined: May 2005
Posts: 167
B
Member
Instead of putting a dead short on the cable, one could use a resistor. Then you could identify between an open cable, a shorted cable, or a cable that has the correct resistance on it and is therefore intact and the one you want.

You could use a 75-ohm terminating resistor for this. It's already packaged in an F connector, so you could just use an F81 splice barrel and connect it straight to the cable you want to test.

In a lot of cable systems, you don't really even need a TV. Just use an FM radio (not a digital one, just a cheap analog tuning model with an antenna). Even if the cable system isn't rebroadcasting any FM stations (most aren't anymore), there are several cable TV channels with their audio in the FM band:

95 has it's audio at 95.75MHz
96 has it's audio at 101.75MHz
97 has it's audio at 107.75MHz

You could also use a radio scanner. I've used a scanner to identify cable signal leaks...just tune it to an audio carrier in the range that the radio can tune and then bring it's antenna near your cables. Should you start hearing the TV audio, you have a signal leak.

Here is a list of all the cable channel frequencies. Note that you must add 4.5MHz to the visual carrier to get the audio carrier:

http://www.jneuhaus.com/fccindex/cablech.html

Another way to check for signal, the cheapest way I can think of:

Since the video carriers are AM one could build a simple crystal-set style detector circuit in conjunction with a high-impedance amplifier or earphone. I expect this will emit a strong 60Hz tone (the vertical sync) when connected to an active cable line. This can be done with nothing more than a diode.

Several years ago when I used a cassette-tape adapter to feed my car stereo the input from my mp3 player, it did a fine job of picking up the video carrier's vertical sync and blasting the 60Hz tone through my car stereo speakers anytime I drove by a TV transmitter tower.

So I believe a simple detector circuit will work just fine for the purposes of checking for signal on a cable TV line.


Joined: Dec 2003
Posts: 886
H
Member
Instead of putting a dead short on the cable, one could use a resistor.

At one time a long time ago we used to use a 9 volt battery and a DC voltmeter. Then we got smart and used a toner and probe.

As to your other methods to look for signal, remember that analog is either gone or soon will be gone on most cable systems. The actual channels are in groups within several digital carriers.

-Hal


Joined: May 2005
Posts: 167
B
Member
That's true, but the data carriers make a distinctive sound when tuned with an AM tuner, so you could still use a scanner that is capable of picking up AM to check for signal. (Many scanners can, because the aircraft band is AM).

Joined: Jan 2003
Posts: 1,429
L
LK Offline
Member
Originally Posted by cableguy619
As a cable technician, I recommend/request the following: DO NOT PUT THE SPLITTER IN THE ATTIC!!!!!!!!!! Run the new line back to the existing splitter, and either use an unused port on that splitter, or add another splitter to the existing one.


Why do you want to do things the right way, an electricans first pirority is figure how cheap and fast it can be done!

Last edited by LK; 05/18/08 09:17 PM.
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