Tips to improve your SNRHelpful tips from a cable/phone guy to improve your Signal to Noise Ratio (SNR)
2007-11-23 11:20 by Lar
I'll make this long and sweet. I'm new here, so please be patient. Background: I was a preventive maint. tech(main line trouble shooter) for over 7 years. For 3 years now, I'm a central office technician for SBC that wires high speed connections from dsl to OC192's.
If you're looking to improve the signal to noise ratio (SNR) on your cable line, then you've come to the right place. To best explain what that is, imagine your cable signal as a full swimming pool. All your channels and paths are floating on the surface, sailing along. Harmful things that can cause noise are eating holes in the bottom of the pool, therefore lowering the water level. The lower the water, the more hazardous your sailing is. Your boats start to hit rocks and come back to shore damaged.
Here's some simple home wiring tips for all of you on cable hook-ups that want to keep your household pool filled to the rim with water!
1) WIRE QUALITY - This was THE number one pain in the neck for us. If you want the best protection for your signal, stay away from wiring up your own outlets. The best quality wire is not found at your local Radio Shack as much as they like to tell you. The cardinal sin of home wiring is improper shielding. Take a look at your wire. Your signal travels across the copper center conducter. It should have a good layer of WHITE FOAM insulation(as opposed to a somewhat clear plastic). Around the white foam, you should have a minimum of one layer of alluminum foil and one layer of alluminum braiding. IF YOUR WIRE IS COPPER BRAIDED ON THE OUTSIDE, THROW IT OUT! This is EXTREMELY important! The copper braiding does not shield your signal properly. Not only is your cable signal leaking out, but thousands of outside signals are leaking IN, killing the reverse path. My best reccomendations for home wiring would be to use cable size RG-6...the best being quad-shielded(two layers of foil and two layers of braiding). RG-59 can be excepted, but it loses more power of long lengths of cable than RG-6. The thicker the cable, the less loss of db power over distance. You can usually find this type of cable(along with some nice tools) on ebay for a decent price. Also, this applies to all jumper cables behind your tv's and vcr's also! Don't use those easy push on cables, they're junk.
2) KINKS - The minimum bending radius on your cable wires in the house should be about 4". What does that mean? Simple...wherever your cable is turning a corner, either up in the rafters, behind the outlet, or the wire coming from the wall, you should have no direct corners. The bending radius is gotten from putting a loop in the cable, and it should be a minimum of 4" in length across. Keep this in mind when putting in wall outlets. Kinks in the shielding and center throws off your path.
3) TIGHT CONNECTIONS - All cable connections THROUGHOUT the home should be tight. IMPORTANT:Never use a wrench to tighten any connectors from the wall plate on out...this includes your tv's, vcr's, stereos, recievers, and modem! The inside connectors on these are very weak and easy to break, possibly causing your tuner to break down on you! All other connections before these should be tightened by fingers, then LIGHTLY wrench tightened snug. Be very careful not to mistread.
4) WHAT A GOOD CONNECTOR LOOKS LIKE - This can be a pain for most people, so I always recommend having outlets done by the cable company in your area. However, if you want to do your own work, I suggest using LRC connectors. They use a compression fitting with a plastic backing. By using these versus your typical crimp-ons, you keep the integrity of the cable by not kinking it.
Look at the connector...if you look at it from the side, the copper center conucter should be no longer or shorter than 1/8 " sticking out. The more common being shorter, you may still have a signal without the copper center actually touching. This is because it is jumping across the connection, thereby creating an opening for noise. Looking from the top of the connector, make sure there are no pieces of braiding near the center condutor. If just one of this thin pieces is touching, you're grounding out your connection. Peel it away or cut it off with small scissors or snips.
5) SPLITTER QUALITY - Ugh, the ugliest part of noise...this is the part that makes me hate the Wal-marts of the world. I know, nobody wants to have the cable guy come out and put in that extra outlet for $40, so Avereage Joe heads out to the hardware store and buys the biggest splitter he can find...and HEY LOOK! It's got an amplifier, too!....Dumbest move you can make(I'll pick on amplifiers last). Store bought splitters are very cheaply made and not shielded well at all. On top of that, most do not have the proper frequency range. Example: The cable system in your area is sending out their forward signal(channels, etc.) in the 50-1000mhz range, with the reverse path going back to them in the 5-40mhz range. You buy a splitter that is 5-600mhz. You lose half of your upper channels. More often than not, the spliiters don't even have reverse path capabilities, which is how your cable box and modem operate.
The bigger the splitter, the more the loss. Here's a quick loss example... Cable signal strength coming into a home is typically about 9db in power at the outside of the house. Once your db gets below the zero level, you're starting to push it. Every time you split a signal in two, it loses 3.5 db, keep this in mind when wiring.
A 4-way splitter is basically 3 two way splitters (split once, then split both legs again), so you lose 7 db on each output. A 3-way splitter is 2 two way splitters, with one of the outputs losing only 3.5 db(the hot leg), and the other 2 losing 7 db each. 8-way splitters lose 10.5 db on every single leg. Please keep your loss levels in mind when wiring up multiple outlets.
6) AMPLIFIERS - Never, never, never, never use store bought amplifiers. Only about 1 in 20 will work properly with your forward AND reverse path. You can try and find out from your cable company which amp's have been through research and development for positive testing on their signal, but most of the time they won't help. Not only does an amplifier boost signal, it also will boost your noise floor. It is very important to have the amp installed at a location BEFORE you reach 0 db in signal strength.
7) SEALED OUTLEts - Any outlet in the house or splitter connection that is not currently being used should have a screw-on 75 ohm terminator. This will seal the connection from being a port for noise and leakage.
That's about all I have time to help for now, and I hope I've been able to be a good addition to this fantastic website. If anyone has any further questions regarding wiring, please feel free to post a reply.
P.S....If you've got a roof antenna, MAKE SURE IT'S NOT ONE OF THE WIRES CONNECTED TO YOUR CABLE!
Thanks for reading,