4G and Low Phone signal

[lucids]

I am aware that 4G provides only internet data while HSDPA, HSPA+ and 3G do both data and mobile calls but since changing to a 4G LTE contract the signal is very odd. For example.

The icon may indicate 4G on my phone and the signal is very weak just the 1st bar only. At this level speedtest gets about 10-15Mbs data speed but it is almost impossible to get decent call quality. Now when I switch off LTE and switch to High speed packet data Only the signal jumps to 6 bars. I get about 8-10Mbs data and perfect call quality. In the phone settings I can  choose GSM or 3G individually or both or all 3 including LTE.

Why is it then when i have a weak 4G signal (ie only 10-5Mbs 4G data) can I not have a full mobile talk signal to make calls. Note that when I tested and switched to GSM only the signal was full strength as well so when I am on 4G LTE with this weal signal what is being used to make the calls if both GSM/3G signals are good on their own.

Note that when on 4G and full signal the data speed jumps to around 50Mbs.

[MI5]

From what you are saying it sounds like O2 may be testing VOLTE. What area are you in?
As soon as I press send to make a call my signal immediately switches to 3G.

[PhoneChanger]

Lucids what handset do you have?
I experience the same as MI5 in that as soon as I make a call my phone display changes from 4G to H for the call, and then takes a minute or so after the call to connect back to 4G

[lucids]

Sorry i only just saw these replies now, I'm in Leeds and the handset is an HTC One SV sim free running jellybean 4.22

[MI5]

Has is settled down now since November....?

[lucids]

Well i figure they have repaired the mast near my home which was offline, so no signal for nearly a year. Can't believe it took them so long!! They also a little while ago upgraded one mast fairly near to me to 4G. But generally  still the same things happen. When on 4G and you take or make a call the indicator drops down to "H" or "3G". It is not possible to mailtain a 4G signal and make a voice call. Also the phone defaults to 4G and shows the signal bar say at 1 or 2 bars but if you switch off LTE on the phone you can get a full signal for High speed packet data.

[MI5]

What you describe is perfectly normal.
You can't make calls over 4g and the 4g/3g signals are not directly comparable - despite O2 saying they would be.....