I have a Clear hub express w/120' of cable and a 8dbi omni directional antenna. Clear transmitting tower is about 1.5 miles away (not line of sight). Is there any way to improve my reception from that Clear tower ?
If you mean 120ft of antenna cable that may lose more than the 8dbi antenna gains. Take the unit outside on a dry day and connect the antenna directly to the hub and put the whole thing on the roof if possible. You should then be able to use a long ethernet cable to connect to the device to test. This will likely be the very best you could ever get.
So if this works you either try to find a way to mount the device outdoors in a waterproof container.
You other option is to find a device that is designed to operate outdoors. They make a number of these routers for the various LTE carriers. It been a while since I have used a clear device so I don't know if they run LTE or they still run WiMax. LTE you can likely move the sim to a compatible device. WiMax the vendor will have to have a special unit for clear. One company that makes units like this ...not sure about clear though is called bandrich