completion, the power LED will light steadily. The settings for the four hybrid circuits are stored in non-volatile memory and will be recalled during the power-up process.
Level Meters
The Model 46 contains eight 5-segment LED level meters. These meters are pro- vided as a support aid during installation, configuration, operation, and trouble- shooting. The meters represent the sig- nals coming in from, and going out to, the 4-wire connections. The meters are organized in four groups each represent- ing one input and one output. They are calibrated to reflect the level in dB rela- tive to the configured nominal operating level. This is similar to the way in which now-legacy VU meters functioned. As an example let’s take the situation where the nominal operating level of an interface is configured for +4 dBu and an output (“to
4-wire”) LED labeled “0 dB” is lit. (For this example, the level on the 2-wire PL circuit is just large enough to light the “0” LED.)
This indicates that a signal with an approx- imate level of +4 dBu is present on the as- sociated 4-wire output connector. Another example would be a Model 46 interface configured for +8 dBu operation and a –12 dB LED is lit. This indicates that a signal with audio level of –4 dBu is present on its associated output.
Each level meter contains four green LEDs and one yellow LED. The four green LEDs indicate signal levels at or below the configured nominal level. The top LED is yellow in color and indicates a signal that is 6 dB or greater than the nominal level. An audio signal that causes the yellow LED to light doesn’t necessarily indicate
an excessive level condition, but it does provide a warning that at some stage reducing the signal level may be prudent. Normal operation with normal signal levels should find the meters lighting near their 0 dB point. Signal peaks may cause the yellow LEDs to flash. But a yellow LED that lights fully during normal operation will typically indicate a signal level or configu- ration problem.
If the “from 4-wire” meters display consis- tency lower or higher levels than their 0 dB points it’s possible that a configuration is- sue exists. One potential problem is incor- rectly set 4-wire nominal audio level DIP switches for one or both of the Model 46’s interfaces. If the nominal level is set too low then sufficient audio headroom might not be available. It can also result in ex- cessively-high audio signals being sent to 2-wire party-line circuits. Setting the nomi- nal level for too high a value will reduce the signal-to-noise performance. And, as expected, it may also result in audio sig- nals being sent to the 2-wire circuits at too low a level. Begin a review by confirm- ing that the two 4-wire level DIP switches associated with each interface are set as required.
If the Model 46’s 4-wire nominal levels are set correctly but the meters still reflect sub-optimal levels, the issue may be relat- ed to incorrect settings on the equipment connected to the 4-wire inputs and out- puts. It’s possible that although a connect- ed 4-wire device’s nominal level matches the Model 46’s level setting, its actual nominal level may be significantly differ- ent. With a digital matrix intercom system this problem could be due to an incorrect configuration having been made to a spe- cific channel or port. For example, the RTS
