Designed node equalization is the "starting point" for desired tilt with specific equipment, levels and distortions respectively. Certain variables can and will cause these tilts to vary. This can be anything form "reflections" seen at the node testpoint to the difference in manufactured individual TX/RX's. Bottom line you need to get the ""results". If you have various tilts with the same equalizer, obviously, your normalization will be off upon sweeping. It is normal to vary the EQ about 1-2 values from design depending on the equipment used.
The distance of the fiber WILL NOT cause tilt, GLASS IS FLAT in that respect. BUT, the RF input to the LASER's may possibly have tilt. CONFIRM that each laser has a FLAT input. This can cause tilt differences in field. (Flat in Flat out, Tilt in Tilt out). CONFIRM that any unused ports on splitters/taps feeding the laser inputs are TERMINATED in 75-ohms. If not, the unterminated open ports will possibly cause reflections at the input of laser and a "reflection" and "tilt" at specific channels can occour.
Look at the "RAW" sweep (no refernece) with Stealth a the reciever to determine if you have a "TILT" issue due to the TX/RX difference (straight line tilt) , a "REFLECTION" causing this problem (note you will see the STANDINGWAVE) or just a bad TX/RX.
Confirm if your node launch amplifier/node has a RESISTIVE of a "COUPLED" testpoint. If "COUPLED", you have a decent and more accurate indication of what you are seeing. IF it is a "RESISTIVE", well, reflections will occur since there is NO ISOLATION if you have a close coupled splice of device (DC, PI, splice, tap, 90, ect...) at the output. The reflection will cause tilt error to be seen.
Personally I have seen a Philips TX/RX combination and was within 1dB. The MSO replaced the TX in headend with a GI laser(s) and this changed by another 2-1/2dB. Mixing and matching vendor TX/RX in theory should not affect the tilt, but, then again...
Good luck! If you are having problems, feel free to call for further advice!
Greg Tobin
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(314) 422-4423 cellular
