INTRODUCTION

• Electricity always follows the path of least resistance
• Fiber optic cables are not designed to conduct AC power
• Categories of broadband signal transmission components
  • Cable/connectors
  • Passive devices
  • Active devices
• In the return path, line splitters and DCs actually combine return signals arriving from separate feeder runs
• Tap insertion loss is the signal loss between the tap's input and output ports, not to be confused with a tap's value.
• Typical types of amplifiers
  • Bridger amps
  • Distribution amps
  • Line extender amps

• AC waveform characteristics
  • Frequency,
  • Wavelength,
  • Amplitude
• True AC waveforms are symmetrical
• A freq. of 60 Hz means the waveform goes through 60 complete CPS
• Wavelength is distance occupied by 1 complete cycle of hertz
• As freq increases, wavelength decreases
• Amplitude is applied voltage at the peak of a half circle
• Types of AC waveforms
  • Sine wave
    • Most common
  • Square wave
    • I or E don't continuously vary in magnitude
  • Saw tooth wave
    • I or E start at zero and increase linearly
  • Quasi-square wave
    • Has a slightly rounded shape at its min/max peak values
    • This type allows for extended time at max peak values while having a non-instantaneous rise and fall time
• Waveform characteristics
  • Frequency
  • Wavelength
    • Wavelength concerns the physical distance the current moves along a conductor during 1 cycle of the waveform
    • Wavelength is indirectly, or inversely, proportional to frequency
    • As frequency of I or E increases, the wavelength of 1 cycle decreases and vice versa
  • Period
    • The amount of time for completion of 1 cycle of current
    • If it takes 1 second for completion then the period is 1 second
    • Period is inversely proportional to frequency
  • Phase
    • Waveforms are 'in-phase' as long as they cross the 0 horizontal at the same time
  • Amplitude
    • Maximum level of 1 half cycle, either positive or negative

• 5 main points of interest on 1 cycle of a sine waveform
  1. The starting point, 0 °
  2. Maximum point of the positive half cycle, 90 °
  3. Zero crossing between half-cycles, 180 °
  4. Maximum point of the negative half cycle, 270°
  5. The stopping point, 360°

• Waveform Values
  • Peak value
    • Distance between the most positive, or negative peak and the horizontal axis
  • Peak-to-peak value
    • Distance between to most positive and most negative peak of an AC waveform
  • Instantaneous value
    • Used primarily in circuit analysis
    • Value of a single point at a specific moment, or instant, of time
  • Average value
    • Distance between to most positive and most negative peak of an AC waveform
  • The average value of a sine wave is .636 times the peak value of the waveform
  • Effective value
    • The effective value of a sine wave is .707 times the peak value of the waveform
    • Also known as the RMS (Root Mean Square) value
• A non-linear increase involves unequal increases in E or I in equal intervals of time.    Ex. 0 to 3 volts in 2 seconds followed by 3 to 7 volts in 2 seconds, 7 to 12 and so on
• A linear increase involves equal increase in E or I in equal time intervals. Ex. 0 to 3 in 2 seconds followed by 3 to 6 volts in 2 seconds, 6 to 9

• The magnitude of the current is directly proportional to the magnitude of the voltage, but indirectly, or inversely, proportional to the magnitude of the resistance in the circuits
• Voltage and current present in an AC circuit are always in-phase with each other
• Eddy current power loss = I_ec²(R_C)
• Including eddy currents total power in an AC circuit = P = I² (R_S + R_C + R_L) + I_ec²(RC)
• A very high frequency creates much greater amounts of eddy currents than lower frequency
• Skin effect is the concentration of the flowing current near the surface of an AC conductor, compared to the even distribution of current throughout the DC conductor
  • The resistance of the conductor is inversely proportional to the cross-sectional areas of the conductor

• The LE basically increases the signal level of the forward carrier signals after they are attenuated by the coaxial
• 2 Types of housing gaskets
  • Silicon rubber
  • Mesh RFI
• Cooling fins dissipate heat generated by the RF amp module and DC power supply
• Parts of an LE
  • Input
  • Output
  • Test ports
  • Port to module
• LE Powering
  • LE amps require an AC input voltage and a regulated +24 VDC power supply
  • A low pass filter only passes low frequencies
  • LE's either a linear or switching power supply
• Test points (powering)
  • Has both AC and DC test points
• RF Passive devices
  1. Attenuator pads
     • 1 pad in the forward path located before the EQ and preamp
     • 1 pad in the return path located after the return amp and EQ
     • Pads reduce the amplitude of the forward path RF signals or the return path RF signals
  2. EQ
     • Is installed before the preamp to compensate for the unequal signal
     • level attenuation caused by the coaxial cable leading up to the LE amp
  3. Filters
     • Used to filter out or block specific frequencies from passing through the filter
     • Diplex filters separated higher forward frequencies from lower return frequencies, when a return path is used
     • Typically installed at both the input and output of module
     • Contains a high and low pass filter
       • High pass filter blocks lower frequencies below a specified frequency
       • Low pass blocks higher frequencies so they don't interfere with the lower frequencies return path signals used in the return path
• Controls and test points
  • Slope
    • Adjusts the amplitude of the RF output signals to compensate for tilt of coaxial downstream
    • Located after preamp
    • Slope is accomplished by
      • A plug in EQ and IS EQ
      • Automatic slope control
• Amp Forward Path
  1. Forward RF enters at Port 1 and is routed to a high pass filter
  2. At the HPF, RF is separated from any 40-60 VAC
  3. HPF directs RF to input DF
  4. HPF also directs AC to
     1. DC power supply where the AC is converted to 24VDC for internal amp powering
     2. The thru power fuse where the 60 VAC can be directed to the output 3 port for downstream powering
  5. Input diplex filter passes higher frequency RF signals to the attenuation pad where they are attenuated as needed
  6. RF is routed to the 1^st EQ
  7. After slight ampage in the preamp, slope can be applied using IS EQ
  8. Following the IS EQ, RF is applied to IGC (IS gain control) where the output signal level is set to compensate for 4 dB or 11 dB of cable
  9. RF is again passed through a HPF to block any low frequency signals and noise by entering the PIN diode attenuator
  10. PIN diode and ALC provide continuous level control of RF to final amp
  11. After passing through the PIN Diode, RF is amped in the final amp to required levels
  12. Amped RF is passed through 1^st DC where RF is sent to
      1. Majority of signal is sent to output diplex filter via DC through leg
      2. Small portion of RF is sent to 2^nd DC via 1st DC tap leg
  13. In the 2^nd DC, RF is again divided and sent in 2 directions
      1. Majority of RF is sent to ALC circuit via DC through leg
      2. Small portion of RF is sent through DC's tap leg to provide a forward balancing test point at 25 dB below normal output levels
  14. A small portion of RF is used in the ALC circuit to provide a reference level that controls the PIN diode signal attenuation prior to the final amp stage
  15. The RF signal from the 2^nd DC through leg passes through a multiple channel bandpass filter that allows only a selected frequency to pass to the detector
  16. The Detector converts the RF signal reference level into a control voltage that is adjusted to an appropriate level by the sensitivity control
  17. Control voltage is then amped and sent to the PIN diode, where it controls the amount of attenuation applied to RF signal going to final amp
  18. Forward RF is routed from 1^st DC to output DF
  19. ODF separates forward RF from lower frequency return RF signal
  20. After passing through the ODF, forward RF are combined with the 60 VAC at the HPF
  21. Signals are then directed to output 3 for downstream

• A separate module that plugs into the forward amp module
• Or directly mounted on the circuit board in the amp module itself
• Bandpass filters pass a particular group of freqs while rejecting another group of freqs that might cause interference
• A HPF is a type of BPF that passes all freqs above a specific freq and eliminates common path distortions, impulse noise in the return spectrum and any other freq that falls below the specific freq

• A bridger housing has 4 outputs for either
  • Entering a tap directly
  • Passing through feeder, splitters, DCs, LE's or other taps
• Fiber optic cables are NOT designed to conduct AC power
• Express cable is employed for signal and power transmission between the forward signal outputs of an optic node and the input of a distribution amp
  • There are NO TAPS installed on an express cable
• 1% change in the cable attenuation for every 10° F change in the cable temperature
• Abnormal attenuation changes
  • Moisture
  • Physical damage
  • Electrical abnormalities
    • Impedance discontinuities
• Return Loss
  • The difference in dB between the signal power applied to a terminated cable and the reflected signal power
  • The larger the ratio value in dB, the smaller the amount of reflected signal voltage
  • Structural return loss occurs with physical structures of the cable change
• Feeder signal transmission component categories
  • Cable/connectors
    • 2 Types of cable
      • Aerial (messenger)
        • Jacketed
          • Additional corrosion protection
          • More cable support
          • Improved handling characteristics
          • Greater life expectancy
          • Reduced surface friction during pulls
          • Some degree of electrical insulation
        • Unjacketed
          • Reflects sunlight (reduces attenuation during warm months)
          • Lower cable weight (lower stress on cable)
          • Easier detection of damage
          • Faster cable preparation
          • More economical
      • Underground (Flooded)
      
      
    • Bending radius for Commscope cable

      .500	8.0"
      .625	9.0"
      .750	10.0"
      .875	13.5"
      1.000	15.0"

      
      
    • 2 Types of center conductors
      • Solid copper
        • Stronger, more durable, lower DC resistance
      • Copper-clad aluminum (CCA)
        • Lighter, cost less, equal attenuation at higher freqs
        • 2 Types of dielectric
          • Polyethylene
          • Air
        • 2 Types of connectors
          • 2 piece
          • 3 piece
  • Passive devices
    • Line DC
    • Power inserter
      • A passive device that combines the AC power with the transmitted RF signal
      • AC power conducts in both directions: upstream and downstream
      • Forward and return only travel in one direction and are blocked from the power supply
    • Splitters
      • A splitter's internal isolation is the port-to-port attenuation between two output ports at a specific frequency with the input port terminates
      • Minimum internal isolation values range from 18-30 dB between 5 and 1000 MHz
      • Passes both RF signal and AC voltage
      • Return loss (see definition)
      • Most hard-line RF splitters can carry a maximum of 10 to 15 amperes
  • Active devices
    • All 4 have a 75 Ω impedance and the ability to simultaneously conduct AC and transmit signal
• Standby power supply components
  • Ferro resonant transformer
  • Batteries
  • AC inverter
• 3 basic cause of outages
  • Powering failures
    • Utility power failure
    • Tripped utility breaker
    • Spent battery
    • Blown feeder leg fuse
    • Blown amp DC power supply fuse
    • CC suck out
  • Cut/damaged cable
    • Cut/damaged underground feeder by a backhoe, trencher,, shovel, etc
    • Aerial by lightning or downed power lines
    • Aerial by traffic accident or sever weather
  • RF equipment failure
    • Amp module failure
    • Damaged passive transmission components (Taps, DC, splitters)