The popular K Series, from DTT reception experts FR, has undergone some developments and now includes an additional Automatic Gain Control feature.

Launched two years ago, the channelised filters and amplifiers have become an ideal solutions to the problems of closing the gap between analogue and digital channels, making digital terrestrial TV easy to distribute. Not only does the K series system allow control of the level of each individual channel, whether adjacent or not, it acts as a very efficient filter to keep unwanted interference from the system, thus improving the carrier to noise ratio, which is particularly important for digital signals.

With the introduction of AGC, the launch signal levels will not change once set. So if the transmitter levels are adjusted or the received levels change, the AGC compensates the gain to ensure the set level is maintained. So now the installer can filter, amplify and control the level of each individual channel, whether analogue or digital, adjacent or stand-alone.

This is particularly useful where transmitters are being re-aligned and power levels increased. Too much signal can be as much of a problem as too little. Most DTT receivers can cope with a maximum 80dBuV of analogue signal and 70dBuV for digital signal. Using K series AGC ensures that this maximum is not exceeded.

Ideally, the input level should be between 80 and 85dBuV analogue level, with a maximum of 95dBuV. Where the digital level is 17 to 27dB lower, the installer can reduce this difference to 15dB.

The K120A has an AGC dynamic capability of 30dB and an output level adjustment between 110 and 120dBuV. Because K series is built in modular, single channel amplifiers, the full 120dBuV maximum output is available for analogue channels and the digital channels would normally be set 15dB lower at 105dBuV (dcp).

When off-air levels are below the ideal, a screened masthead amplifier or K series pre-amplifier can be added to the input to lift levels in order to achieve maximum output. De-rating of the launch level may be required in the normal way where cascading of amplifiers is employed.

So now, where levels of digital and analogue signals change over time for various reasons such as transmitter adjustment, environmental effects, weather and seasonal reasons the new FR K series with AGC takes control. Typically, an 11 channel digital and analogue UHF head-end with AGC can be built for under £500 making K series superb value for money.