I’m not a modem expert or anything, but this might be a good reference for those who have signal or battery issues (or just have the itch to flash something). Anyone who has additional info/corrections, post it here or shoot me a PM and I’ll add it to this post.
DISCLAIMER: Me, Android Central, or any member of these forums, are not responsible for what you do to your phone.
What is a modem?
The modem (aka radio) is basically the software portion of the cellular radio in your phone. This has an effect on signal (obviously), and battery life.
Why do I care?
If you’ve never flashed a ROM and don’t plan to, then this probably isn’t something you should worry about. The modem that came with the last OTA update will be the best 99% of the time. However, if your signal diminished with an update, and you’re willing to flash something, then you might be interested in “downgrading” to an older modem.
If you’re using a custom ROM (I9000 based in particular), you may have more to gain. If you use an I9000 based kernel, you will use an I9000 based modem, NOT one made for the Captivate. These work just fine most of the time, but because they aren’t made for your phone or network, you may run into issues.
How do I know what modem I have?
Setting>About Phone>Baseband Version
When should I try a new modem?
If you are perfectly happy with your signal and battery life (yeah, I know there’s only 3 of you, but it has to be said), then don’t worry about it. If it ain’t broke, don’t fix it. If you’re having issues, then maybe it’s time to flash a new modem. Just be warned, some modems will improve your signal, some will do the opposite. If you’re in a low signal area, and have no way of flashing back right away, then wait for a better situation.
Which modem should I use?
There are two basic rules to modems:
1. Use a 2.1 modem with a 2.1 ROM/kernel; Use a 2.2 with 2.2.
2. Use a Captivate modem with a Captivate kernel, I900 with I900 kernel.
Follow those rules, and nothing will blow up.
Here is a list of commonly used and/or current modems. If none of these work for you, then maybe you’re signal just sucks. All files are flashable through clockwork. Everything is there except Captivate 2.1 JH7, JH3,and JF6.
Captivate (2.1) Modems:
UCJH7 - AT&T Captivate from OTA update
UCJH3 - AT&T Captivate
UCJF6 - AT&T Captivate from stock ROM
If you have the modem file for JH7, JH3,or JF6, please PM me. Maybe I'm just blind, but I can't find them anywhere.
Captivate 2.2 modems:
Link for Captivate modems:
I9000 2.2 modems:
These all have WCDMA 850/1900 (AT&T 3G) enabled by default. I’m not going to clutter this up with modems without these bands. If you want them, they’re all in the modem thread at XDA.
The modems that contain "UG" (or the Telus modem) prefer 850, while the rest prefer 1900. To use a 1900 modem, you must flash an 850 modem first. See below for the procedure.
Link for I9000 modems:
How do I know what to use?
No one modem is better than any other modem. Region, ROM, and other factors can affect which one works best for you. Generally, the more recent the better, but other than that you only have other users’ experiences to go on.
I just flashed a modem, and now I don't have any signal. What do I do?
Most of the I9000 modems default to 1900mhz. You probably live in an 850 area. Easiest way to fix:
1. Start with JK4. It uses 850 as default.
2. Flash a go-between (sort of a middle man). The path seems to depend on the user. I use JK4-KP1-JVE/JQ1, so I would try KP1 here.
3. Boot the phone, and set it down for a few minutes. It has to connect to the 850 band. If it doesn't, make sure you have 850 enabled. If it still doesn't, go back to JK4 and choose a new go-between.
Note: If you live in a 1900 area, there's a good chance you'll lose signal when you go to an 850 area. Have JK4 (and optionally your go-between if you want to use your current modem) ready on your SD card.
4. Once it connects, go back to recovery, choose your modem, and install it.
5. If it boots and you get signal, you're done. Give it a few minutes to lock on. If you DON'T get signal, either choose a new go-between, or add a second go-between (start back at JK4).
Just keep trying different things until it works. If you just can't get it, JK4 will always work with 850. I suggest always having that ready, just in case. (It only takes a minute to change a modem).
What if I need to go back?
Just flash your old modem through clockwork. It's a good idea to keep the file for your old modem on your phone, just in case.
What are your experiences? Have any more questions?
So correct me if im wrong, but do I just flash the new modem to my fone? I read on xda that u need to have a 2.1 rom, flash jh8, then flash 2.2 with a i9000 modem. But since I already have a i9000 rom, can I just flash the modem?
Since you are using a i9000 ROM, you need to use a i9000 modem. JK4 and KP1, the modem from the Chinese i9088, are very popular. And you flash a modem just like you'd flash a ROM or kernel with ClockWork recovery.