RCA Amplitude Modulation Monitor Type BW-66F

Equipment Lost or Damaged in Transit

When delivering the equipment, the truck driver or carrier's agent will present a receipt for your signature. Do not sign it until you have (a) inspected the containers for visible signs of damage and (b) counted the containers and compared with the amount shown on the shipping papers. If a shortage or evidence of damage is noted, insist that notation to that effect be made on the shipping papers before you sign them.

Further, after receiving the equipment, unpack it and inspect thoroughly for concealed damage. If concealed damage is discovered, immediately notify the carrier, confirming the notification in writing, and secure an inspection report. This item should be unpacked and inspected for damage WITHIN 15 DAYS after receipt. Report all shortages and damages to RCA, Broadcast and Communications Products Division, Camden, N. J. 08102.

Radio Corporation of America will file all claims for loss and damage on this equipment so long as the inspection report is obtained. Disposition of the damaged item will be furnished by RCA.

Replacement Parts and Engineering Service

RCA field engineering service is available at current rates. Requests for field engineering service may be addressed to your RCA Broadcast Field Representative or the RCA Service Company, Inc., Broadcast Service Division, Camden, N. J. 08102. Telephone: 609 WOodlawn 3-8000.

When ordering replacement parts, please give symbol, description, and stock number of each item ordered.

The part supplied against an order for a replacement item may not be an exact duplicate of the original part. However, it will be a satisfactory replacement differing only in minor mechanical or electrical characteristics. Such differences will in no way impair the operation of the equipment. Parts with no stock numbers are standard components, not stocked by RCA, and should be obtained from your local electronic parts distributor.

The following tabulations list service parts and electron tube ordering instructions according to your geographical location.

Service Parts

Electron Tubes

Return of Electron Tubes: If for any reason, it is desired to return tubes, please return them through your local RCA tube distributor, RCA Victor Co. Ltd., or RCA International Div., depending on your location. Please do not return tubes directly to RCA without authorization and shipping instructions. It is important that complete information regarding each tube (including type, serial number, hours of service and reason for its return) be given. When tubes are returned, they should be shipped to the address specified on the Return Authorization form. A copy of the Return Authorization and also a Service Report for each tube should be packed with the tubes. (SEE INSIDE REAR COVER FOR LIST OF RCA SALES OFFICES)

List of Contents of Master Item MI-30066-B

NOTE #1: TUBE COMPLEMENT INCLUDED IN ITEM 1 ABOVE COMPRISES: 2 RCA-6AL5, 1 RCA-6C4, 1 RCA-6AQ5, 1 RCA-5814, 2 RCA-884, 2 RCA-OD3, 1 RCA-5V4G.

NOTE #2: THE SUBJECT MONITOR IS AN INSTRUMENT DESIGNED FOR MEASURING THE DEGREE OF MODULATION OF BROADCAST TRANSMITTERS AND FOR FURNISHING AN INSTANT WARNING WHEN THIS DEGREE OF MODULATION EXCEEDS A SPECIFIC SELECTED VALUE.

Instructions

Type: BW-66F AM MODULATION MONITOR (115V., 60 CY.)

FCC Approval No.: 1559

In order to make improvements in design and effect economies in manufacture, RCA reserves the right to make changes in design, components, and specifications published herein.

Front Panel Description (Figure 1)

Figure 1 displays the front panel of the Amplitude Modulation Monitor Type BW-66F. It is equipped with two illuminated panel meters and several controls for operation and adjustment.

Meters

• CARRIER Meter: Calibrated from 80 to 120, with a red mark at 100 indicating the correct radio frequency input level for normal operation.
• MODULATION PERCENTAGE Meter: Features a range of 0 to 120% and is also calibrated in decibels (100% modulation = 0 db). Its ballistic characteristics meet FCC requirements. A polarity switch allows for the measurement of either positive or negative peak values. The accuracy is ±2% of full scale at 100% modulation and ±4% at other percentages. The frequency response is 30 to 15,000 cps ±1/2 db. Terminals are provided for connecting external modulation meters.

The CARRIER LEVEL meter is calibrated from 80% to 120% to indicate carrier level shifts.

Alarms and Indicators

The PEAK INDICATOR, or over-modulation alarm, is a flashing neon lamp that activates when the percent modulation exceeds the level set by the PEAK LEVEL control. Simultaneously, a relay operates, which can be used to control a remote peak counter. The relay remains closed for the duration of any over-modulation peak.

Controls

Four conveniently disposed controls are mounted on the front panel:

• RF INPUT Control: Used for adjusting the signal input to the monitor.
• POLARITY Switch: Allows measurement of either positive or negative peaks, depending on the switch position.
• POWER Switch: Permits the monitor to be turned ON or OFF from the front panel.
• PEAK LEVEL Control: Calibrated from 50 to 120% modulation, used for setting the lowest value of percent modulation at which the overmodulation alarm should operate.

Technical Summary

Electrical Specifications

• FCC Approval Number: 1559
• Power Required: 110 watts, 110 to 125 volts, 50 to 60 cycles
• Fuses: 2 amperes, type 3AG
• Frequency Range: 500 to 2500 kc
• R. F. Input (Nominal Impedance 75 ohms): Minimum: 0.35 watt, Maximum: 6 watts

Audio Output Circuits

Audio Monitoring Circuit

• Source Impedance: 600 ohms
• Level: 1 volt rms at 100% modulation
• Response: 30 to 15,000 cps ±1 db
• Distortion: Less than 1%
• Noise Level: Better than 60 db below the audio level at 100% modulation

Distortion Meter Circuit

• Source Impedance: 20,000 ohms
• Level: 3 volts rms at 100% modulation
• Response: 30 to 45,000 cps ±1/2 db
• Distortion: Less than 0.2%
• Hum and Noise Level (at the terminals): Better than 70 db below the audio level at 100% modulation

Accuracy of Meter

• ±2% of full scale at 100% modulation
• ±4% of full scale at any other percentage modulation

Zero Shift with Line Voltage

Compensated to less than 1.0% for line voltage variation from 110 to 125 volts.

Modulation Range

• 0 to 120% positive
• 0 to 100% negative

Alarm Relay Contacts Rating

• 1 ampere
• 115 volts ac

Mechanical Specifications

Dimensions and Weight

• Height: 8-3/4 inches
• Width: 19 inches
• Depth: 11 inches
• Weight: 37 pounds

Tube Complement (MI-30450)

• 2 RCA 6AL5
• 1 RCA 6C4
• 1 RCA 6AQ5
• 1 RCA 5814
• 2 RCA 884
• 2 RCA OD3
• 1 RCA 5V4G

Crystals

• 2 Type 1N97

Description

General

The Type BW-66F Amplitude Modulation Monitor (MI-30066-B), shown in Figure 1, is an instrument designed for measuring the degree of modulation on the carrier wave of an amplitude modulated transmitter operating on any frequency within the range of 500 to 2500 kilocycles. It was designed to meet the specifications of the Federal Communication Commission as set forth in Section 3.50 (b) of the Rules.

Panel meters indicate both the modulation percentage and the carrier level. Provision is made for connecting a remote alarm, or a counter for recording the periods when the percentage modulation exceeds that desired to be maintained by the station. An over-modulation alarm or flashing lamp is provided to give instant warning when the modulation exceeds the established level.

In addition, two auxiliary audio output circuits operating from a separate diode rectifier are provided. One of these, a 600-ohm impedance circuit, is intended for audible monitoring; the other, a high impedance circuit, gives a faithful reproduction of the carrier envelope with less than 0.2% distortion. The high impedance output circuit can be connected directly to the RCA WM-71A Distortion and Noise Meter, enabling overall fidelity and noise measurements to be made on the transmitter. The unit is designed for standard rack mounting. Two RF INPUT terminals, a POWER receptacle and a terminal board for all other connections are mounted on the back of the chassis. See Figure 4.

Meters

Two panel mounting meters having illuminated scales are provided. The CARRIER meter includes a scale calibrated from 80 to 120 with a red mark at 100. Normal operation is obtained when the pointer is set at this red mark which denotes the correct radio frequency input level.

The MODULATION PERCENTAGE meter has a range of zero to 120% and is also calibrated in decibels using 100% modulation as zero db. The ballistic characteristics of this meter meet the requirements of the FCC. A polarity switch is provided so that either the positive or negative peak values may be measured. The accuracy of measurement of percentage modulation is greater than that required by the FCC, which is ±2% at 100% modulation and ±4% of full scale at any other percentage of modulation. The frequency response of the modulation meter circuit is 30 to 15,000 cps ±1/2 db. Terminals are provided for connecting one or more external modulation meters.

If one or two external meters are used, ballistic characteristics will meet FCC requirements. Use of more than two external meters, however, may result in ballistic characteristics outside the limits specified by the FCC.

The CARRIER LEVEL meter is calibrated from 80% to 120% to show carrier level shift.

Alarms and Indicators

The PEAK INDICATOR or over-modulation alarm consists of a flashing neon lamp which operates when the percent modulation exceeds that set by the manually operated PEAK LEVEL control. Simultaneously with the operation of the flasher, a relay is caused to operate. This relay may be used to control a remote peak counter. The timing of the relay circuit is such that it remains closed for the duration of any over-modulation peak.

The alarm circuit is arranged so that it will operate properly when the modulation frequency lies between the limits of 30 to 15,000 cps. Constant accuracy of alarm operation, regardless of line voltage changes at the power supply input, is insured by supplying regulated power to the circuit. The contact connections of the relay are available on a terminal board at the rear of the instrument. These contacts are designed to carry a current of one ampere at 115 volts.

Audio Output Circuits

There are two audio output sources from the Type BW-66F Modulation Monitor. Refer to Figure 4. One of these circuits is intended to operate the monitor loudspeaker through a suitable amplifier. The impedance of this source is 600 ohms, unbalanced, and the output level is one volt rms with 100% modulation. The frequency response of the monitoring circuit is 30 to 15,000 cps ±1 db and the distortion is less than one percent. Connection to this circuit is made through terminals number 5 and 6.

The second output circuit from the monitor is employed for connection to a distortion meter. The impedance of this source is 20,000 ohms (one side is grounded) and the level is three volts rms with 100% modulation. The frequency response of the circuit is within ±1/2 db between 30 and 45,000 cps and the distortion is less than 0.2% between 30 and 15,000 cps. The hum and noise level at the distortion meter terminals is better than 70 db below the audio level at 100% modulation. Connection to this circuit is made through terminals number 7 and 8.

Controls

The instrument has four conveniently disposed controls mounted upon the front panel. Refer to Figure 1. They are: the RF INPUT control which is used for adjusting the signal input to the monitor, the POLARITY switch which allows either positive or negative peaks to be measured, depending upon the switch position, the POWER switch permitting the monitor to be turned ON or OFF from the front panel, and the PEAK LEVEL control which is calibrated from 50 to 120% modulation is used for setting the lowest value of percent modulation at which it is desired to have the overmodulation alarm operate.

Installation

Mounting

The monitor is designed for mounting in a standard 19-inch rack such as the RCA Type BR-84 (MI-30951 series) Cabinet Rack.

Connections

The RF input terminals, see Figure 4, should be connected to the standard RETMA pickup circuit which is usually provided as part of the transmitter. A 75-ohm coaxial cable should be used for this connection.

Terminals (to which R11 is connected in Figure 4) are provided for the connection, in series, of additional external MODULATION meters when and if desired. When external meters are used, the resistance value of R11 must be reduced by approximately 1500 ohms for each external meter added, in order to maintain a total resistance at terminals 1 and 2 of TB1, including meter(s) of 6500 ohms.

When an external meter is connected to the end of a long line, the resistance of this line also must be included in the total resistance. If no external meter is used, these terminals should be shorted by the 6490 ohm resistor, R11, which is provided for that purpose.

The contacts of the MODULATION ALARM relay K1 are connected to terminals numbers 3 and 4 at the rear of the monitor, see Figure 4. The contacts of the relay have a capacity of one ampere at 115 volts. A peak counter or warning circuit may be connected to these terminals. These circuits should not draw over 1 ampere. Connect the receptacle J1 to a 110-125 volt, 50-60 cycle source.

Operation

With the monitor connected to a 110-125 volt, 50-60 cycle power source and with the power switch S2 in the ON position, put the instrument into operation in the following manner:

1. Set the RF INPUT control to its extreme counterclockwise position.
2. With the transmitter pick up circuit connected to the RF input jack, TB-13, turn on the transmitter. If the pointer of the carrier level meter moves beyond the red mark, adjust the position of the pickup coil in the transmitter to reduce the signal input to the monitor. Only about 0.35 watt r-f power is required to operate the indicator within its normal range.
3. Adjust the RF INPUT control so that the carrier meter reads 100. For stations operating with different day and night power outputs, the pickup coil should be adjusted so that the CARRIER LEVEL meter can be properly set for both power levels by the RF INPUT control.

After these adjustments, the MODULATION meter will indicate the percentage of modulation directly, and of such polarity as is shown on the POLARITY switch. If the modulation percentage exceeds the setting of the PEAK LEVEL control, the PEAK INDICATOR neon tube will light and the MODULATION ALARM terminals 3 and 4 will be shorted by the relay.

Maintenance

Modulation Meter Adjustment

If for any reason the adjustment of the AUDIO LEVEL potentiometer, R19, has been altered from its original setting it may be readjusted in the following manner: With the TRANSMITTER and the MODULATION MONITOR in operation, set the polarity switch to the NEGATIVE position. With the CARRIER LEVEL meter at 100, check the zero setting of the modulation meter. The meter should be adjusted to indicate any residual noise modulation in the transmitter after the modulator is turned off. Then, using 1000-cycle constant-frequency modulation, feed sufficient signal into the transmitter to cause 100% modulation. Adjust the RF INPUT control to set the pointer of the CARRIER LEVEL meter at the red line. Adjust the AUDIO LEVEL control R19 until the modulation meter indicates 100%.

IMPORTANT: In order to obtain an accurate adjustment it is necessary that the transmitter be in proper operation and correctly neutralized.

The meter indication should be the same on either position of the POLARITY switch provided the modulation waveform is purely sinusoidal and no sideband clipping is present in the transmitter.

Procedure for Compensation of 5814 Tube

In order to compensate this tube for variations in line voltage, the monitor should be connected to the power supply lines through a "Variac" or similar voltage varying device. If a "Variac" is not available it will be necessary to check the operation of the monitor at periods of the day when low and high limits of line voltage are encountered.

To compensate for "zero" drift of a 5814 tube proceed as follows:

1. Set the mechanical zero on the MODULATION PERCENTAGE meter.
2. Apply normal line voltage (117 v a-c measured with an accurate voltmeter) to the unit and allow it to warm up for 15 minutes.
3. Using a screwdriver, set controls R4 (ZERO SET) and R41 (BIAS) at the mid-position of their adjustment range.
4. Apply an unmodulated r-f signal to the unit then adjust the electrical zero of the MODULATION PERCENTAGE meter by means of R41 (BIAS).
5. Without changing the setting of R4 (ZERO SET) vary the applied a-c line voltage between the limits of 110 volts and 125 volts. Allow the voltage to remain at each of these limits for at least 30 seconds to stabilize the heater temperature, then note the amount of zero shift on the MODULATION PERCENTAGE meter at each limit.
6. If the zero shift is greater than 1.0%, change the setting of R41 (BIAS) slightly, then restore the meter zero by adjusting R4 (ZERO SET).
7. Again vary the line voltage between the specified limits as described in step 5 and note the amount of zero shift. If the shift has increased from the previous value, change the setting of R41 (BIAS) in the opposite direction past the original position. Readjust the meter zero by means of R4 (ZERO SET). A decrease in the amount of zero shift indicates that R41 has been moved in the correct direction and should be moved still further this way. Readjust the meter zero by means of R4 (ZERO SET).
8. Repeat the procedures in steps 5 and 7 until a setting is found for R41 (BIAS) which gives a zero shift value of less than 1.0% when the line voltage is varied between 110 volts and 125 volts.

Flasher Circuit

When the flasher circuit is properly adjusted, the PEAK INDICATOR neon lamp, I-1, will just begin to flash when the percentage modulation set by the PEAK LEVEL control corresponds to the percentage modulation indicated by the MODULATION PERCENTAGE meter. If the RCA-884 MODULATION ALARM tube has been changed, or the adjustment of R19 disturbed, readjustment should be made as follows: With sufficient carrier and modulation to give an indication of 100% on the MODULATION PERCENTAGE meter, set the PEAK LEVEL control knob at 100. Then adjust the PEAK CALIBRATION CONTROL 'A', indicated in Figure 2, until the neon lamp just flashes. Reduce the percentage of modulation so that the MODULATION PERCENTAGE meter indicates 50% modulation. Set the PEAK LEVEL knob to 50, and adjust the 'B' PEAK CALIBRATION control until the neon lamp just flashes. Repeat these adjustments until the threshold operation of the neon lamp is obtained when the PEAK LEVEL control and the MODULATION PERCENTAGE meter indicate 100% and when the control and meter indicate 50%.

Fuses

When replacing a blown fuse, make sure that the replacement fuse is of the same type and rating (3 amperes, type 3AG) as the one furnished with the monitor. To replace a fuse with one of higher rating will needlessly endanger the equipment.

Typical Tube Voltages

Voltages measured to ground except V4 and V5 filaments. No signal on input. AC line voltage 117 v, 60 cycles. All voltages DC unless otherwise indicated. DC voltages measured with 20,000 ohms/volt meter.

Diagrams and Schematics

Figure 1: Amplitude Modulation Monitor - Type BW-66F (MI-30066-B) - Front Panel.

Figure 2: Front Panel Lowered.

Figure 3: Rear View of Front Panel.

Figure 4: Rear View of Chassis.

Figure 5: Amplitude Modulation Monitor Type BW-66F (MI-30066-B) Schematic. This diagram illustrates the internal electronic circuitry, showing the arrangement and interconnections of tubes, resistors, capacitors, transformers, and other components. Key values and symbols are provided.

Figure 6: Amplitude Modulation Monitor Type BW-66F (MI-30066-B) Wiring Diagram. This diagram details the physical routing of wires and cables throughout the chassis and front panel, including connections to terminal boards and components.

Parts List

The following tables detail the components used in the Amplitude Modulation Monitor.

Capacitors

Diodes

Fuses

Lamps

Connectors

Relays

Chokes/Reactors

Meters

Resistors

Switches

Transformers

Filter

Miscellaneous

List of RCA Sales Offices