Capital adequacy ratio

An actual wide-band L pad used to match 50 ohms to 75 ohms.

An L pad is a network composed of two impedances that typically resemble the letter capital "L" when drawn on a schematic. It is commonly used for attenuation and for impedance matching.

Speaker L pad

A speaker L pad is a special configuration of rheostats used to control volume while maintaining a constant load impedance on the output of the audio amplifier. It consists of a parallel and series resistor in an "L" configuration. As one increases in resistance, the other decreases, thus maintaining a constant impedance, at least in one direction. To maintain constant impedance in both directions, a "T" pad must be used. In loudspeakers it is only necessary to maintain impedance to the crossover; this avoids shifting the crossover point.

A constant-impedance load was important in the days of vacuum tube power amplifiers, because such amplifiers often did not work efficiently when terminated into an impedance greatly different than their specified output impedance. This was only true of full range speakers. Most modern applications for full range speakers use tapped transformers. Maintaining constant impedance is less important to modern amplifiers using solid state electronics.

In high frequency horns, the L Pad is seen by the crossover, not the amp. L pads may not necessarily use infinitely variable rheostats, but instead a multi-position rotating selector switch wired to resistors on the back. Tapped transformers are not L pads—low-end manufacturers to the contrary; they are autoformers. L pads can also be used at line level, mostly in pro applications.

Audio-frequency (AF) operation

The L pad attenuates the signal by having two separate rheostats connected in an "L" configuration (hence the name). One rheostat is connected in series with the loudspeaker and, as the resistance of this rheostat increases, less power is coupled into the loudspeaker and the loudness of sound produced by the loudspeaker decreases. The second rheostat is connected between the input and ground (earth). As the first rheostat increases in resistance, the second rheostat decreases in resistance, keeping the load impedance (presented at the input of the L pad) constant. The second rheostat usually has a special taper (function of resistance versus rotation) to accommodate the need for constant input impedance.

Radio-frequency (RF) operation

In RF (radio frequency) applications, the L network is the basis of many common impedance matching circuits, such as the pi network employed in amplifiers and the T network that is common in transmatches.

The L network relies on a procedure known as series-parallel transformation. For every series combination of resistance, R_S, and reactance, X_S, there exists a parallel combination of R_P and X_P that acts identically to the voltage applied across the series combination. In other words, the series components and the parallel components provide the same impedance at their terminals. The transformation ratio is the ratio of the input and output impedances of the impedance matching network.

The series-parallel transformation allows the input impedance to be dropped down to lower impedances while sustaining a voltage across the circuit. This system works in reverse as well. The equations needed for this transformation are as follows:

Q = X_S/R_S= R_P/X_P = [(R_p/R_s)-1 ]^0.5 [1]

R_P = R_S (Q² + 1) and R_S = R_P / (Q² + 1) [2]

X_S = QR_S and X_P = R_P / Q [3]

For the resistance R_s and reactance X_s in series, R_p and X_p exist as a parallel combination. One simply needs to know the input impedance R_p and to choose the output impedance R_s. Or conversely know R_s and choose R_p. Keep in mind that R_p must be larger than R_s. Because reactance is frequency dependent the L network will only transform the impedances at one frequency.

Inclusion of two L networks back to back creates what is known as a T-network. T-networks work well for matching an even greater range of impedances.

Impedance matching

An L pad used to match a source to a load of a different impedance.

If a source and load are both resistive (i.e. Z1 and Z2 have zero or very small imaginary part) then a resistive L pad can be used to match them to each other. As shown, either side of the L pad can be the source or load, but the Z1 side must be the side with the higher impedance.

$R_{b}={\frac {Z_{2}}{\sqrt {1-Z_{2}/Z_{1}}}}\,$

$R_{a}={\frac {Z_{1}Z_{2}}{R_{b}}}\,$

There is an inherent insertion loss $Loss=10\log {\frac {P_{pad}+P_{load}}{P_{load}}}=-20\log {\frac {2{\sqrt {Z_{1}/Z_{2}}}}{1+(R_{a}+Z_{1})(R_{b}+Z_{2})/(R_{b}Z_{2})}}\,$

where $P_{load}\,$ = power dissipated by load and $P_{pad}\,$ = power dissipated by the pad resisters. Large positive numbers means loss is large.

The loss is a monotonic function to the impedance ratio. Higher ratios require higher loss.

Application notes

Speaker L pads are designed to match the impedance of the speaker, so they were commonly available with 4, 8, and 16 Ω impedances.

See also

• Π pad
• T pad

Notes

43 year old Petroleum Engineer Harry from Deep River, usually spends time with hobbies and interests like renting movies, property developers in singapore new condominium and vehicle racing. Constantly enjoys going to destinations like Camino Real de Tierra Adentro.

References

• Silver, H. Ward, Experiment #21: The L-Network (Hands-On Radio), QST, Oct. 2004, pp. 62-63
• Basic Car Audio Electronics: "L-Pads" http://www.bcae1.com/lpad.htm
• Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
  
  Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
  
  In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
  
  Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
  
  Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
  
  15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
  
  To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010

External links

• All About Pads
• L-Pads