LNB Testing of a Satellite Dish

By Richard Asmus

A low noise block (LNB) amplifier placed in the feed horn of a satellite dish picks up the signal and down-converts it to a lower frequency that the receiver can read to select the TV channels. Like all electronic equipment, an LNB can fail. Test an LNB using an internal system test procedure, an external meter or by replacing it with a new one. See the LNB user's manual for power output specifications.

LNB Parts

An LNB has several components. An input filter assures that only signals from satellites enter the LBN. The low noise pre-amp amplifies the satellite signal to a usable level. A local oscillator and mixer down-convert the signal to an intermediate frequency that carries the TV channel information. The output filter removes any unwanted signals that may cause interference, and a final amplifier increases the IF to a more usable level to travel through the cable to the receiver. The output power of an LNB depends upon the strength of the signal received and the design of the LNB.

System LNB Testing

Numerous satellite TV systems installed by service providers such as Dish Network and DirecTV have system tests that reveal a failed LNB. The process of testing a system depends on the model of the receiver, but the user's manual illustrates how to do it. Your TV screen shows the results of the system test. If the LNB is not functioning properly, a message will display that clearly says so. Run a system test using your remote control. If a defective LNB message appears, call your service provider to send a technician. Service is usually included in your subscription price.

LNB Tester or Meter

Use a meter to test the power of the signal coming out of an LNB. A standard radio frequency power meter will show the level dBm, but it requires external power to operate. The meter may also be expensive. The power output should be from -80dBm to -25dBm. Smaller, less expensive meters designed for home satellite systems connect between the LNB and the receiver. The LNB gets the voltage needed to operate the electronic circuits from the receiver through the cable. An LNB in-line tester uses this power. Install it between the existing cable and the LNB to read the signal level.

Replacement

If you have no resources to perform a system test, or to check the output with a meter, replace the LNB. Check the return policy for an LNB at a local satellite dealer or electronics store. If you buy a new one to replace the one in question, you may be able to return it for a refund if it doesn't fix the problem. See your satellite manual for replacement instructions. Satellite dishes may be installed in precarious locations, and accidents can cause injury or death. If you don't have experience, call a professional technician to test or replace the LNB.