Thanks, Matt.
I have the EM7355 device. I was able to reference the AirPrime Embedded Module EM73xx/7655/8805 AT Command Reference document which provides some very good instruction. Truth be told, I had to brush up on my AT command. It’s been more than a decade since I worked on modem stuff at this level.
After reading over the document, I noticed the AT!BAND command, which according to the documentation, “Configure the modem to operate on a set of frequency bands, look up available sets, create new sets, or return the current selection.” The AT!SELRAT was an option, but looking at the documentation, the AT!BAND option seemed to hard code the band and was the preferred method. I did not see the AT!SELRAT command in the documentation, but it did seem to respond when issuing the AT!SELRAT? command.
After using Putty to connect to the COM port of the Sierra modem, I was able to issue the AT!BAND=2 to hard set to 3G. Please see screen shot of said Putty session. Interestingly enough, I was also able to use PowerShell to script this as well, see below.
# SetWWANBand.ps1
# Forces the WWAN device to use a specific band (3G, 4G, etc)
#set com port to correct port
$port=new-object system.io.ports.serialport com6,9600,None,8,One
$port.RtsEnable=$true
#putting the script to sleep to allow the slow com port to catch up
Start-Sleep -m 1000
$port.Open()
Start-Sleep -m 2000
#BAND=00 for all/auto, BAND=2 for 3G, BAND=4 for 4G
$port.WriteLine("AT!BAND=2`r")
Start-Sleep -m 100
$atstatus = $port.ReadExisting()
$port.Close()