Hi @Dpross96 ,
Based on the information that you have provided that you see 30 Mbps upload, I do not judge that an external antenna would benefit the measured upload bandwidth.
I was in a similar position as yourself and considering purchasing an external antenna costing between GBP 70 to GBP 150 which are prices for which a reasonably capable new router can be purchased.
Luckily I looked into the various signal strength statistics as shown in a Netgear MR1100 (RSRP, RSRQ, RS-SINR) and looked these up online to help judge whether my router was well-positioned. https://usatcorp.com/faqs/understanding-lte-signal-strength-values/
What I found was that the logical and raised position gave a SINR of under 6 dB (poor), but that a different lower position only about 1.5 m away now consistently gives me a SINR of over 12 dB (excellent, and at the moment between 18 dB and 21 dB).
I would recommend that you try a few logical locations where you could alternatively place your 4G router and reboot the router and view your signal statistics if they are made available to you, or if there is some online method to access undocumented functionality. (A bandwidth test really is not a good substitute for view the parameters.) You may also view the tower locations at https://cellmapper.net and move the router to the side of your property where you expect the towers to be.
You may be lucky and find a location where you may get an excellent signal and signal to noise ratio and may save the cost of an external antenna and put this money instead towards a future 5G router (as I intend to). From viewing opinions online, generally on poor networks it is found that the upload speed can exceed the download speed and that is exactly what I found with my previous provider. The fact that you observe 30 Mbps suggests there is a high chance that the signal is find to allow a upload measured bandwidth of a significant percentage of this which is why I do not recommend purchasing an external antenna. If you were to make such a purchase, I would recommend to test both with and without immediately after each other (rebooting router between each) to judge if there is any benefit.
Edit: my findings suggest that if I want to boost my measured bandwidth, I should upgrade from a Cat 4 LTE router. A family member has reported to me that an upgrade to a more modern router was found to double the measured bandwidth in that particular location. Your mileage may vary and none of this may be applicable to your situation. Good luck! 🤓
