TechTalk

Signal Satisfaction

Welcome to Tech Talk, Pico Macom's series of technical notes, featuring useful information and equipment tips. This installment of Tech Talk discusses using Pico Macom signal analysis meters to measure for optimum performance.

Do we really need a meter?

Have you ever said, "I've got good signal"? How do you really know? As an installer, as soon as the install was complete I had the task of adjusting the picture controls on the TV set to mask any imperfections. For a quick check, looking at the TV set is a great way to verify what is seen by the customer. But it isn't a valid way to measure signal quality. There are just too many variables. Signal analysis meters provide a consistent form of measurement to ensure that you are always "comparing apples to apples."

One of the most important aspects of maintaining any headend and distribution system is balancing the signal levels to avoid interference and create uniform performance across all channels. Signal analysis meters such as the Pico Macom PICO-PRO and PICO-TECH will allow system adjustments that enable the other high quality Pico Macom products to perform to their optimum capabilities. At Pico Macom, our staff can assist you with the selection of these and many other high quality products to suit your every reception need.

System Balance & Quality Verification

The first task is to properly balance the signal levels in the headend. The video and audio carrier levels of each channel should be adjusted so that each one is providing the same level of output signal. Channel modulators provide optimum performance when they are adjusted approximately 2dB from maximum output level. Due to slight differences in the circuitry and frequency, this is rarely possible. Slight compromises are made to come as close as possible.

The distribution system should be designed so that each amplifier can be set for unity gain. This means that each amplifier receives the same input level and produces the same output level. Due to the physical layout of the cabling and amplifiers, maintaining consistent spacing may not be possible. Signal attenuators and equalizers can be used to simulate or correct for non-uniform cable lengths.

Set-up and Balancing

Headend Balance: There must be a test point common to all the channels. It is good practice to place a TSC-20 directional coupler prior to as well as just after the launch amplifier. This will provide high level test points for signal measurement and testing.

  1. Connect the PICO-PRO meter to the tap port of the TSC-20 prior to the amplifier.
  2. Set the meter to video carrier mode and adjust the RF/Gain control of each channel to maximum output.
  3. Set the meter to V/A difference mode and adjust the V/A separation to 15dB on each channel.
  4. Set the meter to video carrier mode and check each channel to locate the one with the lowest output level.
  5. Reduce the output by 1dB and match the carrier level of the other channels to that level.
  6. Check the launch amplifier's loading chart to ensure that the maximum input energy level has not been exceeded.
  7. Move the meter cable to the TSC-20 on the output of the launch amplifier.
  8. Set the meter to tilt measurement mode and adjust the launch amplifier output levels to match the level and tilt of the distribution design.

Diagram 1

Distribution Balance: The amplifiers in the distribution system should closely match the levels of the launch amplifier.

  1. Connect the PICO-PRO meter to the amplifier's input test point and set it to tilt measurement mode.
  2. Using TSEQ-2150 equalizers and FAM attenuators, match the inputs as closely as possible to the same input levels of the launch amplifier.
  3. Move the meter cable to the output of the amplifier and adjust the gain and tilt/slope adjustments to match the launch amplifier output levels.
  4. Repeat this for each distribution amplifier.

Diaram 2

Quality Testing

Carrier to noise measurement indicates the amount of static electrical noise in the picture. It will show up as grainy or snowy pictures. To make this measurement, the signal level of the channel to be measured should be between 7~15dBmV. This measurement will give a fairly accurate idea of the added noise into the system.

  1. Connect the meter to the signal under test and set the meter to video carrier mode.
  2. Measure the level of the carrier to ensure that it falls within an acceptable range.
  3. Set the meter to C/N measurement mode and note the reading. This can be done at any location where proper signal levels are available.

Hum modulation measurement indicates the amount of AC voltage that has been introduced into the video and audio signal. This can appear as a series of bars that roll upward through the TV screen. To make this measurement, the signal level of the channel to be measured should be between 7~15dBmV. This measurement will give a fairly accurate idea of the added hum modulation into the system.

  1. Connect the meter to the signal under test and set the meter to video carrier mode.
  2. Measure the level of the carrier to ensure that it falls within an acceptable range.
  3. Set the meter to hum measurement mode and note the reading. This can be done at any location where proper signal levels are available.

Using Pico Macom test equipment products is a snap!

Want To Know More?

View information about PICO-PRO and PICO-TECH