Here's my setup:

I am on the east side of Hamilton with line of site to Te Aroha on a clear day, I have a 43 Element UHF Antenna (http://www.jaycar.co.nz/productView.asp?ID=LT3181&CATID=31&form=CAT&SUBCATID=478) 
on top of a two storey house, I have a  Digimatch VHF/UHF/HDTV Masthead Amplifier
(http://www.jaycar.co.nz/productView.asp?ID=LT3270&CATID=31&form=CAT&SUBCATID=568) in the roof space immediately below the antenna, there's a cable run of about 2m  from the output of the masthead amp to a two-way splitter, from there it's about 8.5m to my HTPC and 12m to my workstation. Both of these have Hauppage Nova-T-500 tuners. All wiring is in Quad shielded RG6 and all connectors are F-type crimp

Here's my problem:

The Hauppauge signal monitor shows a CoN which is usually around 39-41 during which time picture is fine and I get the occasional audio stutter (might not be signal strength related) sometimes it goes up to 45, and occassionaly it drops below 36 and when that happens I get no picture or sound.

Does anyone know what the CoN value from the Hauppauge signal monitor means, and what a good range of values would be?

Here's an extrect from the GBPVR logs:

Workstation:
File GBPVRRecordingService.exe-native-1.log:
2009-07-31 20:28:03.809    VERBOSE    locked=1    present=1     strength=-14000     quality=60
2009-07-31 23:33:03.803    VERBOSE    locked=1    present=1     strength=-14000     quality=60
2009-08-01 22:28:03.751    VERBOSE    locked=1    present=1     strength=-17000     quality=100
2009-08-01 22:48:02.390    VERBOSE    locked=1    present=1     strength=-16000     quality=100
2009-08-02 20:59:19.195    VERBOSE    locked=1    present=1     strength=-13000     quality=60
2009-08-02 21:04:08.451    VERBOSE    locked=1    present=1     strength=-12000     quality=40
2009-08-02 22:18:03.020    VERBOSE    locked=0    present=1     strength=-17000     quality=0
2009-08-02 22:53:02.676    VERBOSE    locked=1    present=1     strength=-15000     quality=100
2009-07-31 20:28:03.809    VERBOSE    locked=1    present=1     strength=-14000     quality=60
2009-07-31 23:33:03.803    VERBOSE    locked=1    present=1     strength=-14000     quality=60
2009-08-01 22:28:03.751    VERBOSE    locked=1    present=1     strength=-17000     quality=100
2009-08-01 22:48:02.390    VERBOSE    locked=1    present=1     strength=-16000     quality=100
2009-08-02 20:59:19.195    VERBOSE    locked=1    present=1     strength=-13000     quality=60
2009-08-02 21:04:08.451    VERBOSE    locked=1    present=1     strength=-12000     quality=40
2009-08-02 22:18:03.020    VERBOSE    locked=0    present=1     strength=-17000     quality=0
2009-08-02 22:53:02.676    VERBOSE    locked=1    present=1     strength=-15000     quality=100

HTPC:
2009-08-01 20:17:05.605    VERBOSE    locked=1    present=1     strength=-17000     quality=100
2009-08-01 20:27:03.180    VERBOSE    locked=1    present=1     strength=-18000     quality=100
2009-08-01 20:29:08.928    VERBOSE    locked=1    present=1     strength=-16000     quality=100
2009-08-01 23:27:03.529    VERBOSE    locked=1    present=1     strength=-16000     quality=100
2009-08-02 18:01:01.104    VERBOSE    locked=1    present=1     strength=-14000     quality=40
2009-08-02 20:27:03.893    VERBOSE    locked=1    present=1     strength=-14000     quality=100


What's wrong with my setup? what can I do to get consistent signal strength and quality?

Thanks in advance.