VRC2000 Installation and Operations Manual Page 85
Technical or Setup Assistance
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necessary to raise R49 to 100kOhms if DTMF receive levels approach
2V peak-to-peak. If a VRC2000 has a low DTMF receive level, the
voltage gain of U16B can be increased by decreasing the value of R49.
• RFI Interference (Poor DTMF Decoding No Auto-Answer)
Typical Reading/Finding
U42 Pin 5 Pulses low during ring.
Ringing voltage must be 30–120VRMS, 15–80Hz RFI audio on phone
line.
Repair Procedure (If Necessary)
RFI problems are cured with any or a combination of the following
methods:
Suggestion l: Correct site grounding problems.
Suggestion 2: Update the phone company’s surge protection.
Suggestion 3: Build a filter.
Suggestion 4: Buy a filter.
The VRC2000 should be grounded using common RF-protection
practices. Avoid wiring that creates ground loops (two different paths to
station ground).
AM RFI is often generated by central office carbon-shunt surge
protections installed from tip and ring to ground. Update this protection
to gas tubes.
AM and FM RFI can be trapped using a filter. Figure 25 (below)
illustrates suggested RFI filters.
The telephone company can provide filters. VRC2000’s installed at AM
sites have performed well with AT&T’s Z1OOA filter.
• Metering System Failure Alarms
Typical Readings
Jl Pins 1–16 less than 10Vdc
Analog Regulator AC ripple less than 30mV peak to peak.
Repair Procedure (If Necessary)
The VRC2000 can only monitor DC potentials up to 10Vdc or 10mA.
The VRC2000 will report metering-system failure alarms if an
instantaneous reading is taken above these limits.
Poor power rectification can only be cleaned up by AC line conditioning.
Figure 25. RFI filter.
Component Values
Disc Caps.
Rated > 100V
L CaCb
AM 22uH 0.0022uF1,000pF
FM 390–500uH 220pF 100pF
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