Is there a way to split a frequency into channels?

Is there a way where I can take a single frequency and subdivide it into channels so theoretically I can transmit multiple voice channels on the other?

I agree with the previous answer that "channel" typically refers to a carrier frequency. For example, each Citizen's Band, marine FM and Family Radio System channel is assigned a unique frequency.

Independent Sideband (ISB) is a method of modulating two different signals onto a single carrier. From Wikipedia,

Independent sideband (ISB) ... modulates two different input signals — one on the upper sideband, the other on the lower sideband. This is used in some kinds of AM stereo (sometimes known as the Kahn system).

According to page 50 of Dellsperger's treatise on Amplitude Modulation,

The practical implementation is realized by addition of an LSB and a USB signal.

This is similar to frequency-division multiplexing,

... a technique by which the total bandwidth available in a communication medium is divided into a series of non-overlapping frequency bands, each of which is used to carry a separate signal.

What you are looking for is called a multiple access method: a way for two or more users to share the capacity of a single channel.

Common ways to do it include:

• frequency division: divide the channel into narrower channels, each user gets a sub-channel
• time division: divide the channel into time slots, users take turns
• code division: each user uses a different spreading code with a low correlation
• space division: each user gets a directional antenna (perhaps a dynamic one, with beamforming techniques) pointed at just them

There are different ways to allow two signal sources to share the same frequency, although I wouldn't call them channels because that word implies different carrier frequencies.

You could use time-division multiplexing (https://en.wikipedia.org/wiki/Time-division_multiplexing). This is the approach used by DMR radios. It's much better suited for digital signals than for analog signals.

Another possibility is frequency-division multiplexing (https://en.wikipedia.org/wiki/Frequency-division_multiplexing). You could, for example, use lower frequencies for one voice and higher frequencies for another voice in your audio stream. This would require electronically altering the pitch of at least one voice. The combined audio would be used to modulate the carrier, and the process would be reversed on the receiving end. This works great for analog signals, but it can greatly increase the bandwidth of the signal. This trick was sometimes used in analog phone networks to reduce the number of wires needed to carry multiple phone calls.

Another option is to rely on polarization. You could use vertically polarized antennas for one conversation and horizontally polarized antennas for another conversation. This doesn't provide perfect separation, but it could be good enough if you're working within line of sight. If you're trying to bounce the signal off the ionosphere, the polarization can be changed significantly.