The message would be 20 times longer (in time), increasing its chance of collision by 20 times and exactly cancelling the 20 times reduction that it gets from randomly selecting one of 20 channels.
But that's also true on 1 channel. Doesn't solve the hidden node problem. You have 1/20 as much risk of starting to transmit at the same time on the same channel as someone else, after you both determined the channel was clear, since that's a race condition with a fixed time window per transmission, but is that the main cause of collisions?
Here's a thought experiment. Remember, there's only one channel.
Let's say you have 100 meshtastic nodes in a residential valley. And you have 1 meshtastic repeater up on a mountain overlooking the valley (or it could be on a radio tower or water tower, say).
So it's clear that most of these nodes won't see each other because terrain, housing, trees, etc.
But it is possible that the repeater may have clear line of sight to most of them. And that's where the hidden node problem lies.
And adding more nodes and more repeaters is not going to help. The problem is either solved by increasing the number of channels (hence the sdr angle) or by time division multiplexing the single channel and coordinating who can talk at what time. The first is easy. The second is much harder.
