of only 2 dB is required. The RTS ADAM™ series of matrix intercom systems has a nominal level of +8 dBu. This level also applies to their RVON-I/O VoIP products. As such, reducing their nominal input and output levels by 4 dB will ensure optimal compatibility.
The Model 45 contains four 5-segment LED level meters with two displaying the level of the signals being received on the
4-wire inputs and two displaying the level being sent out the 4-wire outputs. During installation and setup the meters are in- valuable in helping to confirm that proper operation is taking place. The meters are also useful during normal operation, allow- ing confirmation of audio signal flow into and out of the Model 45.
Pro Audio Quality
The Model 45’s audio circuitry was designed in the spirit of professional audio equipment, rather than that found in typical party-line intercom gear. High- performance components are used throughout, providing low distortion, low noise, and high headroom. Using passive and active filters, the frequency response is limited to nominally 100 Hz to 8 kHz. This range was selected to provide excel- lent performance for human speech, while maximizing the ability of the hybrids to create substantial “nulls.” When the Model 45’s internal DC power source is selected to provide 2-wire party-line intercom pow- er enhanced audio performance can also be expected. The quality of the DC supply circuit is very good, with very little noise, hum, or “hiss” being added to the 2-wire connection. In addition, the impedance characteristics of the interface’s DC powered (“wet”) channel was tailored
to be essentially identical to that of the unpowered (“dry”) channel. This unique situation allows the automatic nulling circuitry to provide excellent, consistent results for both the powered and unpow- ered channel.
Attention to detail is a hallmark of the Model 45’s design. For example, during the brief auto nulling process the interface channel’s 4-wire input and output signals are normally muted, preventing unwanted audio from reaching the connected equip- ment. Associated with the 2-wire party-line interface is circuitry that, under software control, applies 200 ohm terminating impedances to the 2-wire party-line circuit. This, along with other circuitry that moni- tors DC voltages present on pins 2 and
3 of the 2-wire circuit, ensures that audio instability associated with unterminated circuits will rarely occur.
Special Applications
While the Model 45 is designed to directly integrate into typical applications, it’s ready to support the “one-in-a-million” situations too. To accomplish this five DIP switches, accessible on the front panel, allow control over some of the unit’s features. For example, one DIP switch changes the way the auto null pushbutton switch operates. Normally pressing the button begins the process of auto nulling both channels. The alternate switch mode allows each auto null sequence to be activated independently. One “tap” of the auto null button will begin the auto null process for channel 1. Two “taps” of the button will begin the auto null process for channel 2. Another DIP switch allows the auto terminate feature to be disabled. While this feature can help maintain
