T-type Attenuator / T-pad

T-type debilitating is a debilitating network consisting of three non-inductive resistant elements connected together to form a "T" configuration.

Although not so common, this "T" (tee) configuration can also be considered as a wye "Y" debilitating configuration. Unlike the previous L-pad Debilitator, which has a different resistance value when viewed from both ends and makes it asymmetrical, the T-pad is symmetrical in its debilitating design.

The creation of resistant elements in the form of a letter "T" means that the T-pad debilitator has the same resistance value when viewed from both ends. This formation then makes the "T-pad debilitator" a perfectly symmetrical debilitating, which allows the input and output terminals to be displaced as shown.

t type debilitating

In the design of the T-pad attenuator we can see that it is symmetrical when viewed from both ends, and this type of debilitating design can be used for impedance matching of even or unequal transmission lines. In general, the R1 and R2 resistors are of the same value, but when designed to work between unequal impedance circuits, these two resistors can be of different values. In this case, the T-pad debilitator is often referred to as a "taper pad debilitator".

But before looking at T-pad Debilitators in more detail, we need to understand the use of the "K factor", which is used to calculate debilitating impedances.

"K" Factor

The "K" factor, also known as the "impedance factor", is widely used with debilitators to simplify the design process of complex debilitating circuits. This "K" factor or value is the ratio of voltage, current or power corresponding to a certain weakening value. The general equation for "K" is given as follows:

k factor

In other words, the voltage ratio is Kv: Vin/Vout = 10dB/20, current ratio, Ki: Iin/Iout = 10dB/20 and power ratio, given in Kp: Pin/ Pout = 10dB/10.

For example, for a voltage weakening of 6 dB, the value "K" will be 10 (6/20) = 1.9953 and a weakening of 18 dB will be 10 (18/20) = 7.9433. But every time we want to design a new debilitating circuit, instead of calculating this "K" value, we can produce a table of "K" factors to calculate its debilitating loss, as follows.

dB Loss0.
K value1.05931.12201.25891.41251.99532.37142.81843.1623
dB Loss12.
K value3.98117.943315.84931.62363.096251.191000105

Equal Impedance T-pad Debilitating

We've said before that the T-pad debilitator has a symmetrical debilitating design that can replace the input and output terminals. This makes it ideal to place the T-pad debilitator between two equal impedances (ZS = ZL) to reduce signal levels.

In this case, three resistant elements are selected to ensure that the input impedance and output impedance match the load impedance that forms part of the debilitating network. Since the T-pad's input and output impedances are designed to fit the load perfectly, this value is called the "characteristic impedance" of the symmetrical T-pad network.

The equations given to calculate the resistance values of a T-pad debilitating circuit, which is then used for impedance compatibility in any desired weakening, are given as follows:

t type debilitating

K is the impedance factor in the table above and Z is the source/load impedance.

T-pad Debilitating Sample

A T-pad debilitator is required to reduce the level of a sound signal by 18dB when pairing the impedance of the 600Ω network. Calculate the values of the three required resistances.

t type debilitating

Then the R1 and R2 resistors are equal to 466Ω and the R3 resistance is equal to 154Ω or the nearest preferred values.

Again, as before, we can produce standard tables for the serial and parallel impedance values required to create a 50Ω, 75Ω or 600Ω symmetrical T-pad debilitating circuit, since these values will always be the same regardless of application. The calculated values of R1, R2 and R3 resistances are given below.

dB LossK value50Ω Impedance75Ω Impedance600Ω Impedance
R1, R2R3R1, R2R3R1, R2R3

As the amount of weakening required by the circuit increases, the serial impedance values for R1 and R2 increase, while the parallel shunt impedance value of R3 decreases. This is characteristic of a symmetrical T-pad debilitating circuit used between equal impedances.

Unequal Impedance T-pad Debilitating

In addition to using T-pad debilitator to reduce signal levels in a circuit with equal impedances, we can also use it for impedance matching between unequal impedances (ZS ≠ ZL). When used for impedance pairing, the T-pad debilitator is called the Taper Pad Debilitator. However, to do this, we need to slightly change the previous equations to take into account the unequal loading of resource and load impedances on the debilitating circuit.

t type debilitating
Pad Debilitating Equation for Unequal Impedances

K is the impedance factor in the table above, and Z1 is larger than weld/load impedances and Z2 is smaller than weld/load impedances.

T-pad Debilitating Sample

To reduce the level of a sound signal from a 75Ω impedance source by 18dB, a taper pad debilitator connected to a 50Ω load impedance is required. Calculate the values of the three required resistances.

Z1 = 75Ω (largest impedance), Z2 = 50Ω (smallest impedance) and K = 18dB = 7.9433 from the table above.

t type debilitating

In other words, resistance is equal to R1 15.67Ω, resistance is equal to R2 62Ω, and resistance is equal to R3 36Ω or nearest preferred values.

Balanced-T Debilitating

Balanced T-pad debilitating, or Balanced-T Debilitating for short, uses two interconnected T-pad debilitating circuits to create a balanced network of mirror images, as shown below.

t type debilitating

The Balanced-T debilitator is also called an H-pad debilitator, since the layout of its resistant elements forms the shape of an "H" letter, and therefore their name is "H-pad debilitators". The resistance values of the Balanced-T circuit are first calculated as the same unbalanced T-pad configuration as the previous one, but this time the serial resistant values are halved (divided in half) to provide a mirror image on both sides. The total calculated resistance value of the central parallel resistance remains the same value, but is divided into two by producing a balanced circuit depending on the central soil.

Using the calculated values above for the unstable T-pad debilitator, serial resistance is the same as R3 = 154Ω for all four series of resistance and parallel shunt resistance, and can be calculated using R1 = R2 = 466Ω ÷ 2 = 233Ω. The following modified equations can be used for a balanced-T debilitator.

t type debilitating


T-pad is a symmetrical debilitating network that can be used in a transmission line circuit with debilitating, even or unequal impedances. Since the T-pad is symmetrical in its debilitating design, it can be connected in both directions by making a two-way circuit.

One of the main characteristics of T attenuator is the shrinkage of the shunt arm (parallel) impedance as the weakening increases. T-pad debilitators used as impedance adaptation circuits are often called "taper pad debilitators".

We found that T-pad debilitators can be unstable or balanced resistant networks. Fixed-value balancing T-pad debilitators are the most common and are often used in radio frequency and TV coaxial cable transmission lines, grounded on one side of the line.

Balanced-T debilitators are also called H-pad Debilitators because of their design and structure. H-pad debilitators are mainly used in data transmission lines that use balanced or twisted dual cables.

In the next tutorial on debilitators, we will look at another T-pad debilitating design called Bridged-T Debilitating, which uses an additional resistant component in the series line.