Many existing CO DSL modems may only support a relatively narrow receive frequency range, which will increase the difficulty of estimating the much wider bandwidth far-end loop noise.

许多已有的CO(中心局)dsl调制解调器可以只支持相对较窄的接收频率范围，这会增加估计宽的多的远端环路噪声的难度。

youdao

But those bootleg versions have a more limited frequency range and can only receive signals, not transmit them.

FORBES: DARPA-Funded Radio HackRF Aims To Be A $300 Wireless Swiss Army Knife For Hackers