Three types of hybrids are available:

• Resistive hybrid H1RB or H2RB
• Reactive hybrid H3XB
• Skewed hybrid H1SB or H1SB-R

Balanced hybrids are typically used. The H3XB is the only adjustable hybrid. Because of this, it should be used at the tuner-end of the hybrid chain to better match the PLC transmitters to the transmission line. The H1RB is typically used everywhere else in the chain. When losses are of great concern, for example in an extremely long line, an unbalanced or skewed hybrid (H1SB) may be used in place of the H3XB. The higher receiver loss does not affect signal-to-noise ratio since the noise as well as the signal is attenuated by 13 dB.

Skewed Hybrid with Receiver Port 50 Ohm termination (H1SB-R)

This skewed hybrid has the receiver port internally terminated into a 50 ohm load. This eliminates the need for the external resistor, ensuring proper termination of the hybrid for optimal isolation.

Following is a summary of some of the more important hybrid application rules.

• All hybrids in a chain should be type H1RB except the last hybrid (tuner end)
• The last hybrid in the chain should be an H3XB or H1SB
• When using the H3XB transmitters, frequencies must be within 4% for frequencies below 50 kHz and 6% for frequencies above 50 kHz. If these conditions are not met, the hybrid cannot be adjusted to provide good isolation between all transmitters
• When applying transmitters and receivers to an H3XB hybrid, the frequency spacing between the transmitters and receivers is of no concern
• When the last hybrid is a H1SB, terminate it with a 50 ohm resistor to obtain proper isolation between the transmitter and receiver ports or use an H1SB-R.
  

Following are a few guidelines in order of importance for chaining together hybrids.

• Hybrids should be arranged with the lesser losses in the transmitter path and the greater losses in the receiver paths to provide maximum transmitter signal levels onto the power line
• Transmitters used with wide bandwidth channels should be arranged with the lower losses and those of narrower bandwidths should have the higher losses. Narrow-band systems are not as susceptible to noise as are wider band systems
• If possible, transmitters used for common applications should be arranged for equal attenuation (such as Direct Transfer Trip or Segregated Phase Comparison)
  

Characteristics

Hardware

All three Hybrids are available in a metal case measuring 3.25"H by 5.625" W by 5.00" D.

• RF Hybrids ( 267k)