I can only get LTE Cat 2 on the unit, or 3G LTE, I very interested in what you said about limiting the unit because its not a phone etc.
Did you check with the operator they support CAT-6? Sometime you might need to swap to a new SIM (as depends of what internal mgmt-system they use).
Try focus on B3 initially as B20 usually is crowded in rural areas since most devices auto connecto to this band. If you speed test B20 during the day you will probly notice a considerable slowdown at evening time. Btw, do you have an unobstructed line of sight ie is able to see the mast from your place?
Examples of dl/ul speeds for the different categories. These are pure theoretic numbers. In practice you only get maximum of 70% of these even during optimal conditions.
Are you sure you've located all the available masts? The reason I'm asking is that it may be possible that you are trying to point the antenna at a different mast than the mobile initially was connected to when you conducted the tests.
If you have access to an Android there are plenty of good apps that are able to display cell id's and signal strength for the different masts. You may also try field test mode (ie "*3001#12345#*") on some older iPhone models. Avoid the new ones as they have removed much of the detailed info nowadays.
To locate some useful masts, first create a directional antenna by taping the phone inside a colander/strainer, an aluminum pie pan or aluminum foil with a shape that resembles of a satellite dish. For ease of use, start the app and run screen mirroring to a PC connected with an USB-cable. Then try find any masts with good enough signal strength and write down relevant info such as compass direction, cell ID, frequency band, signal strength etc. Use the respective frequency band and cell ID and test the unit to find out which mast that may offer the best speed.
This also give you the opportunity to check what level of carrier aggregation it's possible to achieve as smartphones are rather good to configure and utilize that functionality (IMHO much smarter than the RoS controller and device driver for the LTE modules which is the main reason you have to conduct all these settings manually)
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