Thanks 42dB,
Another thing he may want to try is alternate the combined channels. Back in the 1980's we used to be plagued by beats caused mostly from the channel 4 through channel 6 range when combined harmonically with the rest of our carriers. Depending on what other carrier frequencies and bandwidth the system had, there would be specific "beat spots" that were more effected than others that could show up anywhere.
What would help was instead of combining all channels on one rack per combiner (ch. 2, 3, 4, 5, 6, 7, 8, 9 on rack/combiner #1 and ch. 10, 11, 12, 13, 14"A", 15"B", 16"C", 17"D" on rack/combiner #2) we would alternate combiner channels (ch. 2, 4, 6, 8, 10, 12, 14"A", 16"C" on rack/combiner #1 and ch. 3, 5, 7, 9, 11, 13, 15"B", 17"D" on rack/combiner #2) and do the same with all of the existing channels and racks in the same type format. This did help back in the old days. Now today with more superior equipment and combining networks, this may not be such a concern but should be still be practiced from "old school" experience. The channels used in this example may be different depending on who and how the racks were wired. Normally the lowest frequency to the next highest is used. When you consider the CATV mid-band and the FM channels, it gets sometimes confusing since there ARE channels between channel 6 and channel 7.
Many of the old modulators and processors were in need of a "comb generator" that would work similar to a Automatic-Frequency-Control (AFC). The comb generator would produce a carrier every 6-MHz and be wired throughout the racks to EVERY modulator and processor to keep the modulator from drifting. Sometimes this technology would malfunction and "beats" would be a problem depending on if the generator was off, not connected to a specific modulator or a specific modulator was not properly aligned for the carrier it was tracking to.
Enough of my babbling! This actually brings back memories talking about this stuff. Hard to believe some of the crap we used to have to do to make it work correctly. This stuff isn't in textbooks or in the user manuals. It is just "been there, done that" experience. Just like sharing ideas so others don't have to sweat through what was already done. No need to reinvent the wheel!
Greg Tobin
Interactive Broadband Technical Services, LLC
314-422-4423 cellular
Re: Rainbow effect
Member #: 7190
Registered: 1996-2001
Posted:
483
Name:
Greg Tobin
Name:
Greg Tobin
Company:
Interactive Broadband Technical Services
Occupation:
HFC Engineer/Consultant
Location:
www.interactive-broadband.com
Personal:
Experience:
~45 years
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