We recommend that the antenna attenuation should not exceed 20dB if not using an amplifier. If an amplifier is needed we recommend using the Tallysman TW125 in-line amplifier, this will provide a gain of 25dB.
Without an Amplifier.
Using CNT 240 Antenna cable we recommend a maximum length of 60 meters (195 ft)
Using RG 58/U Antenna cable we recommend a maximum length of 32 meters (104 ft)
Using CNT 400 Antenna cable we recommend a maximum length of 100 meters (327 ft)
With an Amplifier
Using CNT 240 Antenna cable we recommend a maximum length of 137 meters (449 ft)
Using RG 58/U Antenna cable we recommend a maximum length of 71 meters (232 ft)
Using CNT 400 Antenna cable we recommend a maximum length of 250 meters (820 ft)
Note: Tekron does not stock CNT 400 or RG 58/U.
A useful site to lookup different coaxial cable attenuation figures can be found here