When selecting a single-sideband voice transmitting frequency, what minimum frequency separation from a contact in progress should you allow to minimize interference?

A standard Single-Sideband (SSB) voice signal occupies a bandwidth of approximately 2.4 to 3 kHz. To avoid overlapping with an ongoing contact and causing splatter or adjacent-channel interference, you must leave at least 3 kHz of separation between your operating frequency and the frequency of the other stations. Leaving only 150 to 500 Hz of separation is far too little, as this is merely a fraction of a voice channel's width and will result in severe interference. Conversely, leaving 6 kHz or 10 kHz is overly generous and wastes valuable spectrum space on crowded bands.