850 mHz Coax Collinear

So I've been trying for some time to get decent signal strength on a 850 mHz trunked P25 system in my area (Rhode Island RISCON). I'm about 30 miles out, and I just can't quite get clear receive. I made a 5 element folded dipole yagi that will get clear receive if I get on my roof with it directly attached to the scanner, but still not enough signal to make it down any length of coax into the shack.



I figured I would try making a coax collinear as described at this link:



Build A 9 dB, 70cm, Collinear Antenna From Coax



I really didn't expect success considering how precise the measurements seemed to be and the amount of connections to be made, but I figured I'd give it a go anyways. I adjusted the measurements from the above link for the 800 mHz band, and actually it wasn't that bad to build.



Once constructed, I headed up to the roof (BTW scanner is a 436HP) and to my surprise, I've improved from one bar on the s-meter to three!!!



But here's the problem... despite much stronger signal strength, when a transmission comes in the decode is much worse than with 1 s meter bar on the yagi, barely readable if at all.



My question is... could poor construction of the collinear (and I admit it was a bit shabby) result in improper phasing of the received signal, causing a garbled RF signal despite the apparent significant increase in signal strength? Or could the omnidirectional gain be causing multipath reception problems?



The antenna outperforms a 1/4 GP when mounted at the same height and through the same coax on the local MA SP trunked system, so I know at least I am getting some gain.

850 mHz Coax Collinear