Theoretically, you can use an unlimited amount of walkie-talkies on the same channel (although in practice you might experience a few problems if you took that suggestion literally). Basically, there isn'ÂÂt really a set limit. You could use as many as you like provided they are set up correctly. Anybody set to the right channel and in range at the time of transmission would then be able to pick up the signal and respond to it.
Most radios have access to 8 channels. These channels each have 38 separate ÂÂidentification tonesÂÂ. The user sets his/her channel up with the desired tone and then only other users who know the channel/tone will be able to hear the transmissions. As a result, there are, in any given area, about 304 different combinations, so signal interference is unlikely to affect you.
Please do not interpret this answer as saying that your radio has access to 304 possible channels. It does not. It will likely only have access to 8. Some less reputable manufacturers tend to falsely imply access to 304 channels; this is simply not the case. You will have access to 304 possible tone/channel combinations, thatÃ¢ÂÂs all.
To better explain the CTCSS codes and how they work; we'ÂÂll include a little information from Amherst.co.ukÂÂs FAQ page.
ÂÂCTCSS stands for âContinuous Tone Coded Squelch Systemâ. These codes are also often called âPrivacy codesâ If a CTCSS tone is selected; a CTCSS sub-audible tone is transmitted along with the regular voice audio by the transmitting radio. The receiving radio, set to the same CTCSS tone, will only receive audio if it contains that sub-tone. Interference from other users on the same frequency is therefore rejected (unless they are also on the same sub-tone). This is a way of allowing groups of users of walkie-talkies on the same channel to avoid hearing messages from other nearby usersÃ¢ÂÂ.
So, in conclusion, you can probably use as many walkie-talkies as you like on the same channel. As long as the units in question are of the same type (either VHF or UHF) and have the same CTCSS setup, then you simply shouldn'ÂÂt have a problem. You also shouldn'ÂÂt suffer from signal interference due to other users (although you may still experience signal loss/interference/degradation from other sources). We have talked about combating signal loss elsewhere, so please see the other questions if you have any problems in this area.