Folks, my report on the week's roller-coaster investigations, and a relatively happy conclusion...
Thanks to everyone for all the suggestions and analysis, all massively useful! Turns out the all singing Huawei 5G router CANNOT make use of a 4G external antenna, despite Huawei's tech support team's insistence that it would.
Special thanks to zzing123 who posted this :
There might be a problem with that antenna, as you're using the Gigacube being a 5G device with 5G radios. The issue with the Gigacube (aka Huawei 5G CPE Pro) is that the external antenna is ONLY for 5G. 4G uses only the internal antennas. So I fear you have is a 4G antenna that isn't feeding the required frequencies to the Gigacube.
I plugged in an old DLink 953 4G router to our Poynting XPOL/A0002 directional antenna and up popped our Vodafone signal offering 10Mbps DL and 20Mbps UL! Router config is somewhat basic, but claims to see signal of -91dBm. Very pleased!
Also thanks to those who suggested EE. I tried an EE SIM in the same router and achieved a reliable 6Mbps DL and which also improved on attaching the external antenna allbeit the omnidirectional A0001 as we aren't pointing the best direction for the EE transmitter.
Special growls to
* Huawei tech support who insisted the H112-370 was capable of using an external antenna for 4G (and not just 5G as is the actual case) and to
* Vodafone who supplied us with the 5G router knowing we are not in a 5G area and failed to highlight their router's lack of support for 4G external antennas after several tech chats with us discussing which of their (non-5G) transmitters to point our external 4G antenna towards. Grrr.
Performance testing continues into next week - I've been in a happy places before only to find the initial signal tails off or is affected by something that wasn't present on day one!
I'm now wondering what my best router option is. The DLink is very functional, but getting a bit old I believe, so might be worth getting a more up to date box of tricks. Any suggestions?
Also found a really useful application called LTE HMonitor which connected to the Huawei router and gave be some great stats and monitoring capability. It's Huawei specific, sadly. Does anyone know of a generic equivalent I could use with my DLink router?
Thanks loads, fab forum, totally saved my bacon!
Cheers
Iain