minecraft-java-editionminecraft-redstone
When I create really big circuits and I go some distance away, the redstone mechanisms stop working and freeze. And if I come back they are still frozen. I have to click on a wire or repeater and place it again to get it working again. My circuit is too big for me to keep all of the chunks loaded by myself, and I can't open minecraft ten times and connect all clients to the server and place all players around the circuit.
Can I expand the area where redstone works?
If I understand your question correctly, here is a way of creating a "power ripple". Think of the sandstone blocks above-ground as ground level; I built it this way so it's easier to see. The circuitry would be underground.
Repeaters have an interesting property of being able to "power" blocks, causing the blocks to give power. Each Repeater in this image is powering the sandstone block in front, turning the Redstone Torch on top of them off, and is also powering the next Repeater.
When this button is pressed, the Redstone Torch turns off, causing the chain of Repeaters to slowly turn off, which also causes the Redstone Torches underneath to slowly turn on, in order.
The result is the line of Redstone Dust on the surface gradually turns on, and then gradually turns off.
To start things with, let me clarify something from the comments on the question. Placed(fixed), in the world, blocks, items and even flowing water or lava, are not considered entities.
Per the minecraft wiki
Entities encompass all dynamic, moving objects throughout the minecraft world.
Here is a list of entities in minecraft: Types of Entities
The reason your wheat farm is not working, is because crops require at least one player to be in their chunk update radius.
Basically, your farm system works, but because the crops never grow, the villagers can't replant anything.
Your iron golem farm is working because, it does not require any player to be in its chunk update radius.
Events processed in spawn chunks
Some extra information on crop growth requirements: Crop growth requirements
Something to note about spawn chunks:
Spawn chunks will not be unloaded from memory, regardless of how far away a player moves, so long as there is at least one player in the overworld. All overworld chunks (including the spawn chunks) are unloaded 60 seconds after the last player in the overworld enters the Nether or the End.
In your case, I believe that the chunks do not get unloaded, due to your sending an item through the nether portal(items on the ground are considered entities).
Best Answer
By default, a 21 chunk by 21 chunk area (with the player at the center) is loaded for each player on a server. The simplest solution is to build your circuits so that they use both vertical and horizontal space to fit them within that area. If this is not possible, then you will need either a plugin (bukkit server) or a mod (vanilla server) to manually load the chunks. It is important to remember however, that this will cause an additional load on the server, so the first solution is still preferable.
Here is the mod that I use to load areas:
Chicken Chunks - http://www.minecraftforum.net/topic/909223-162-smp-chickenbones-mods/
A simple search on the bukkit plugin site will yield a number of options. I cannot suggest one over another, especially without knowing what version you are running.