4g LTE bands 3 and 20

[Wildcat]

I have noticed that my Huawei router B535-235 keeps changing bands from 3 to 20 and back again.  On band 3, the DL speeds are about 40mb and UL under 1mb. On band 20, the DL decreases to about 15mb and UL increases to about 7mb. Any reason why it should do this?  
I have an external antennal (2 cables) fitted and when connected to the ext antenna, it switches between bands 3 and 20 fairly frequently. But when I disconnect the ext antenna, the router favours band 20.

I am in a very rural and remote location with only 1 mast to connect to.

[bristolian]

Band 20 is a single 5Mhz carrier at 800Mhz and is primarily a coverage enhancement layer at edge-of-cell locations.

Band 3 depends on your local config, but is likely to either be a 15Mhz or 20Mhz carrier at 1800Mhz - these are EE's primary mid-band deployments.

I suspect your router is at the edge of B3 coverage and is naturally flipping between the 2 layers.

[Wildcat]

Thank you @bristolian I suspected that may be the case.  Is there any way of configuring the router/antenna to pick up B3 or B20 or a combination of either depending on DL/UL?  

I have found a program called LTE H-monitor which is how I've been able to well when the router switches between bands.

Do you happen to know if B3 is more for towns and B20 more for rural/remote areas or vice versa?

[Wildcat]

Ext Antenna connected 

[Wildcat]

Ext antenna disconnected (router only)

[bristolian]

Ah, you're not far from Torridon in the Highlands - I know the area well.

B3 is EE's base layer and the overwhelming majority of sites have this.

B20 is the "extended range" coverage layer which provides additional coverage in rural & indoor locations. In the Highlands & Islands, the vast majority of sites are B3/B20-equipped, although there are some remote locations where sites only have B20-installed. One's not far from you actually, but they're very much the exception rather than the norm,

The standard B3 carrier is 20Mhz-wide, B20 is 5Mhz wide, hence B3 will generally give better performance and is intended to be higher priority. If radio conditions are too poor for B3 to reliably work, then B20 kicks in. Precise speeds will always vary depending on site/sector loading at the time.

[Wildcat]

Thank you @bristolian , the mast closer to me (behind me and hidden by hills) is a B3 only and in any case I can't connect to it due to the topography. The only mast I can connect to is the one I mentioned above, which is 3.6km (as the crow flies) from me.  I've tried putting the router in the loft at the highest point and it's made little difference, then I was outside up a ladder up to the apex of the gable end, and that too made little difference to speeds etc.  My only other options are to try and rig up some sort of repeater that is further away from the house and trees with better LoS to the mast, and then aim that back to the house or run cabling, but this would need power, either mains or battery/solar - all of which is likely to cost.  My only other alternative is Starlink.  I don't suppose you would know if they plan to upgrade the mast I connect to do you?  I suspect the trees around it might also be hindering the signal.

[Wildcat]

and by the way, would you say my Huawei B535-235 is old and only a base model?  I have tried a TP-Link AC1200 Archer MR600 v3 router and I would say there was not much to tell between them, but then if they are both not getting a decent signal, then that could be why.

[bristolian]

FYI you have a short time after posting to edit, negating the need for multiple short replies.

Trees & vegetation would hinder all RF to some degree. Tech-adds are an ongoing process, I don't know any plans for the Diabaig site specifically, but as I mentioned, the vast majority of sites in the Highlands & Islands are B3/B20. Single B3-only sites often have different antenna, radio & rigging setups to dual-band ones.

Sorry, but I don't have any experience of routers that would qualify me to comment. Active repeaters would generally need to be Ofcom-approved to avoid interference with the macro network.