Coaxial & Speaker Cable Signal Loss

[Big Daddy]

Please review the following threads:

A Guide to Optical, Digital Coaxial (Interconnect & Sub), and Speaker Cables
Impedance & Sensitivity of a Speaker, & Damping Factor

COAXIAL & SPEAKER CABLE SIGNAL LOSS

Signal loss (attenuation) is a problem in both audio and video. However, the results can be more severe and easier to notice in video than in audio. If your TV picture looks grainy, snowy or if there is pixelation, it is most probably caused by a weak signal reaching your TV. You can easily solve the problem by using a signal amplifier to boost the signal. TV signal amplifiers are not very expensive and can cost from $20 to $100+.

There are generally 4 main causes for signal loss:

1. SPLITTERS
2. CABLE LENGTH ATTENUATION
3. CONNECTORS
4. THIN CABLES (such as RG-59 for TV}

1. SPLITTERS:
   
   Splitters are probably the single biggest cause of signal loss. Any splitter from $1 cheap splitters to $20 fancy splitters will have some signal loss.
   
   
   
   
   
   
   These are some losses for TV signal splitters:
   
   Typical signal Loss per port
   
   

   2 way:    - 3.5 dB per port 
   3 way:    - 5.0 dB per port 
   4 way:    - 7.5 dB per port 
   6 way:    - 9.0 dB per port 
   8 way:    - 10.5 dB per port

   This is a relatively large amount of loss, and the most important reason why the picture looks snowy and grainy.
   
   
2. CABLE LENGTH ATTENUATION:
   
   Generally, the longer a signal travels over a cable, the more signal it loses. Another important factor is the signal frequency. Digital TV such as HDTV run at the 550+MHz frequency. The signal loss at this frequency and higher is pretty severe.
   
   
   Typical Coax Cable Signal (Attenuation) Loss per 100ft
   
   

            RG-59    RG-6   RG-11 
   1MHz     0.4dB   0.2dB   0.2dB
   10MHz    1.4dB   0.6dB   0.4dB
   50MHz    3.3dB   1.4dB   1.0dB
   100MHz   4.9dB   2.0dB   1.6dB
   200MHz   7.3dB   2.8dB   2.3dB
   400MHz   11.2dB  4.3dB   3.5dB
   700MHz   16.9dB  5.6dB   4.7dB
   900MHz   20.1dB  6.0dB   5.4dB
   1000MHZ  21.5dB  6.1dB   5.6dB

   
   Signal Loss Per 100 Feet for RG-6 Cable
   
   

    54 Mhz (analog TV):     - 1.50 dB 
   550 Mhz (digital TV):    - 4.65 dB 
   650 Mhz:                 - 5.09 dB 
   750 Mhz:                 - 5.50 dB 
   862 Mhz:                 - 5.93 dB

   Signal Loss for Belden RG-59 B/U Per 100 Feet:
   
   

      1 Mhz:       -  0.6 dB
     10 Mhz:       -  1.1 dB
     50 Mhz:       -  2.4 dB
    100 Mhz:       -  3.4 dB
    200 Mhz:       -  4.9 dB
    400 Mhz:       -  7.0 dB
    700 Mhz:       -  9.7 dB
    900 Mhz:       - 11.1 dB
   1000 Mhz:       - 12.0 dB

   Comparing a digital TV signal vs. analog TV signal, it is like adding another splitter.
   
   
3. CONNECTORS:
   
   Each connector typically may lose between 0.25 to 0.50 dB. Depending on the number of connectors used, this can be like adding another splitter.
   
   
4. THIN CABLES
   
   RG-59 cables are generally thinner than RG-6 cables and many people use them because they are cheaper. The loss of signal for RG-59 is approximately 30% higher than RG-6.
   
   As far as speaker wires are concerned, you can use the following table as a guide:
   
   
   
   
   
   
   

ELECTROMAGNETIC AND RADIO FREQUENCY INTERFERENCE

Another factor that can affect the quality of a signal is EMI/RFI interference. Electromagnetic fields may cause distortion of the signal. Electromagnetic interference (EMI) is any undesirable disturbance which causes an undesirable response, malfunctioning or degradation in the performance of electrical equipment.

EMI affects a circuit either by conduction (electric) or radiation (magnetic). Electric fields tend to have high frequency and magnetic fields tend to have lower frequency. Conductance is caused by physical contact of the conductors. Radiation is caused by induction without physical contact. This can cause mutual inductance between two conductors and result in EMI. Conducted EMI, for example, is unwanted high frequencies that reside on the AC lines. Radiated EMI is similar to an unwanted radio broadcast being emitted from the power lines. Most often, conducted EMI is found in the low frequency range of several kHz to 30MHz and Radiated EMI is found in the frequency range from 30MHz to 10GHz. Most of the EMI interference problems are caused in the range from 100 kHz to 1 gHz.

The terms EMI and RFI are often used interchangeably. EMI is referred to all frequencies of electrical noise, whereas RFI is a subset of electrical noise where radio frequencies operate.

Shielding Against EMI
Most high frequency interference waves are reflected off a conductive shield material. However, the low frequency magnetic waves can penetrate the shield. Therefore, the absorption characteristics of the shield become more significant. This depends on the magnetic permeability and the thickness of the shielding material. Magnetic permeability is the ability of a substance to magnetize in a relatively weak magnetic fields. For high frequency electric fields, thin conductive materials like silver, copper, aluminum foil, nickel zinc and nickel work well as shielding material. For low frequency magnetic fields, you will need a permeable material such as steel.

The purpose of a shield on a coaxial cable is to block EMI energy and redirect it to the ground so that it doesn't reach the center of the conductor. To be effective, a shield needs three things:

1. High coverage, so that energy cannot pass through the holes in the shield.
2. Good conductivity, so that the energy that enters the shield can be redirected to the ground.
3. Good connection to ground at both ends of the cable.

The two most common types of shield are braid and foil.

Foil: A cable can be wrapped in a foil, most often aluminum. Foil offers the advantage of complete coverage. It is a very easy to apply foil to a cable and cover it entirely by attaching the foil to tape, most often mylar. It provides 100% coverage. Aluminm Foil has two disatvantages. First, it has high resistance and is not a good conductor of EMI energy to the ground. Second, The connections of the foil to the ends of the cable conductor are not very reliable and can be compromised.

Braid: A cable can be wrapped in a braided mesh of tiny wires. The coverage of braid shielding is not as good as foil. At best, a braid shield can offer 95% coverage. Conductivity of braid, particularly copper braid, is excellent and the connection to the ground is more reliable.

The effectiveness of the two types of shields varies with the frequency of the interference. Braid is generally more effective at lower frequencies, while foil is more effective at higher frequencies (RFI). That is why we need both types of shields to be 100% effective in blocking noise.

Measure of Shielding Effectiveness
The effectiveness of a shield is measured by what is called Transfer Impedance, which indicates the extent to which a signal outside of the cable reaches the inside. Transfer impedance varies with frequency. The lower the transfer impedance number, the more effective the shield.

GENERAL CONCLUSIONS

1. In home theater applications, you can run an audio cable carrying a line level signal up to 10 meters (32 feet) without any significant signal loss. With longer cables you might notice some attenuation at highest frequencies.
   
2. In professional audio, they use balanced cables (XLR or TRS) up to 200 meters (650 feet) without noticeable loss. This applies to both audio interconnects and microphones with balanced connectors.
3. Generally speaking, signal attenuation may not be the major problem when you use very long runs, but the noise picked by the cable can cause problems. This can be reduced by using well shielded cables, routing them away from noisy sources, separating cables, and paying attention to grounding issues (avoiding ground loops).
4. Ordinary analog audio cables can be used with digital audio signals for distances less than 10 meters. Typically, the impedance of most analog cables are from 40 to 70 Ohms and below the impedance of S/PDIF coaxial cables. This may result in signal reflection and jitter causing bit errors, particularly if the cable length is very long.

REFERENCES

http://www.audioholics.com/education...er-cable-gauge
http://www.delcowire.com/rs_signal_l...ance_chart.asp
http://www.bluejeanscable.com/articles/shielding.htm
http://www.dropamp.com/1.html?err=1
http://www.radio-ware.com/products/t...o/coaxloss.htm
http://www.epanorama.net/documents/video/videocoax.html
http://www.dslreports.com/faq/cabletech?text=1