Most circuits accept -20dB as a reasonable working level, however some circuits can work with isolation levels below 20 dB. Reed relays typically isolate signals down to -40 dB at lower frequencies (1 MHz to 200 MHz) and fall off to -20 dB in the 2 GHz to 3 GHz range. The diagram shown here illustrates relay contacts where a pulse is incident on one end of the open contacts. Note that a small part of the signal leaks through the contacts at the higher frequencies.