There is no real way to measure this. Typically overall Loop length is about 1000 ft.(305 meters). The limiting factor to Loop length is Loop capacitance. An IQ Loop should not exceed 30nf capacitance per loop. We use a calculation for this that includes the number of components. athough components do not acually add capacitance we add them into the equation to compensate for the minute signal drop that occurs as the signal goes though each device. The equation is:
Loop capacitance=
[(wire length in Feet)x(Capacitance of wire per foot in pf/ft)]+[(number of components per Loop)x60pf]
Loop capacitance=
[(wire length in meters)x(Capacitance of wire per meter in pf/M)]+[(number of components per Loop)x60pf]
There are three guidelines to follow with this equation:
1) Wire capacitance should not exceed 30pf/ft (90pf/meter)
2) Add 60pf for every component on a loop.
3) Loop capacitance should not exceed 30nf.
The lower the loop capacitance the longer the Loop can be.
Another thing to remember is that noise induced on the IQ Loop can also cause components to drop off line. I recall one install were the IQ system would drop off line just before a game started. What happened was after the contractor installed the IQ system another contractor came in and laid a loop antenna wire, to bring the local broadcast station into the stadium, in the same cable tray as the IQ loop. This antenna wire wasn't energized until just before a game. It induced enough current to jam the IQ Loop.
I have attached the IQ loop troubleshooting guide, from the old IQ School it should help you with your trouble shooting.
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