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The Electronic Industries Association (EIA) subcommittee on Digital Audio Radio (DAR) and the National Radio Systems Committee (NRSC) Subcommittee on Digital Audio Broadcasting (DAB) met August 24-26, 1995, in Monterey, California, to review the results of the laboratory tests of the nine systems proposed for digital radio in the United States. The Test Working Group B of the EIA DAR Subcommittee has completed the laboratory tests for the nine proposed DAR systems. Of these, four are intended to operate in the VHF (88 MHz to 108 MHz) FM band, one in the medium wave band (AM), one in the satellite S band, and one in the terrestrial broadcast L band. Of the four systems intended to operate in the FM band, one of the systems is designed to operate on in-band/adjacent channels (IBAC), and the remaining three are proposed to share existing channels. The in-band/on-channel (IBOC) DAR system tests have been conducted in partnership with the NRSC.

The DAR tests were conducted in two laboratories, the transmission tests at the laboratory at NASA Lewis Research Center (LeRC), Cleveland, Ohio, and the expert subjective audio tests at the Communications Research Centre (CRC) Psychoacoustics and Subjective Assessment Laboratory, Ottawa, Ontario. The tests at LeRC were conducted in two phases, digital and in-band compatibility. The digital phase evaluated quality and characterized the signal failure. Additionally, the digital tests included multipath, co-channel, and adjacent channel impairments. The in-band compatibility phase of the transmission tests were conducted at the transmission test laboratory. This phase included tests to measure possible interference to the existing analog program services caused by the introduction of in-band DAR. Comprehensive tests were also conducted to assess the compatibility of analog and digital subcarrier (ancillary services channels) with the in-band IBAC and IBOC signals. For the in-band compatibility tests, the committee approved the selection of five consumer receivers for the FM band and three for the AM band. The receivers selected are representative of the existing analog receiver population.

Threshold of audibility (TOA) and point of failure (POF) tests for the digital systems were conducted by the laboratory specialists at LeRC. The results of transmission tests were digitally recorded at the transmission laboratory and sent to CRC for assessment.

In-band compatibility objective tests were also conducted at the transmission laboratory. Digital audio tape recordings were made at the output of the analog compatibility receivers for subjective evaluation by industry experts.

The EIA DAR Subcommittee Test Working Group B on testing started meeting in the summer of 1992. The working group completed a laboratory test plan, established a transmission test laboratory, selected a subjective testing laboratory, characterized the transmission multipath for the FM band (88 MHz to 108 MHz), and completed the laboratory testing process.

The nine DAR systems that were presented to the working group by the DAR Subcommittee have been divided into four subgroups. Table I shows the proponent, frequency band of operation, and the designated subgroup. Two of the proponent systems include a second mode of operation, Eureka 147 and AT&T/Amati, resulting in a total of nine systems to be tested.

The laboratory test results that were presented in Monterey filled two three-inch ring binders, comprised over 1,200 pages, and plotted a wide range of performance data. From co-channel interference to audio transparency using various "stress test" selections,to subcarrier performance in the presence of IBOC and IBAC digital carriers, few stones were left unturned. As with all standards setting processes, this work has not been without controversy. Numerous internal debates occurred over testing methodologies, and the fairness of revisions to certain systems after commencement of testing was actively discussed. Although the final report from the subcommittee charged with that responsibility is months away, numerous claims of "superior" performance in one category or another have been cited on DAB discussion groups by vested interests. While we hesitate to add to those controversies, we note that the well presented results of the audio impairment tests did reveal not unexpectedly, that the high channel rate new band system (Eureka 147 using MUSICAM coding at 224 kb/s) was the only system that showed no discernible impairments after rigorous testing. NPR participated in these tests by providing expert listeners Rich Rarey and Caryl Wheeler for the Canadian Research Commission's audio evaluations. Also note, however, that one IBOC system, USA Digital System I (within the FM emission mask, side band energy only), scored as the first runner up, but suffered discernible impairment on two of the six audio selections under laboratory conditions. The field tests will reveal perhaps the most relevant data on system performance and, especially important for in-band systems, the extent of degradation to existing services. The field tests are scheduled for completion by early 1996.

Leap Second Scheduled for December 31st,1995

The International Earth Rotation Service has announced the introduction of a time step to occur at midnight on December 31, 1995. Coordinated Universal Time (UTC) will be retarded by 1.0 seconds to account for the continuing slow down of the earth's rotation. Although all time scales will be affected by this adjustment, Loran-C, GPS, and OMEGA systems will not be adjusted physically. Instead, the leap second correction for GPS time will change from being ahead of UTC by 10 seconds, to being ahead of UTC by 11 seconds. International Atomic Time will move from being 29 seconds ahead of UTC to 30 seconds ahead of UTC.

Stations utilizing time signals within the Public Radio Satellite System should notice no change unless notified by the Distribution Division in Washington, D.C. The Distribution Division strives for the least disruptive transition point for insertion of the time step prior to the commencement of morning program distribution. Watch the DACS for further details.

OSHA Lockout/Tagout Compliance Sign Available Through NAB

The Occupational Safety and Health Administration's "lockout/tagout" rules are especially important when working with high voltages such as those commonly found at transmitter sites. The rules require stations to establish a procedure for controlling hazardous electrical energy and to train employees in the use of the procedure.

Normally, this requires the source of energy for hazardous equipment to be "locked" in the OFF position. If "locking" the circuit breaker or power switch for the equipment can not be effected, then the breaker or switch must be turned OFF and tagged with a sign warning others NOT to turn the power back on. The typical policy and procedure adopted at stations forbids anyone other than the person affixing the "tagout" warning sign from removing it.

Note that only equipment subject to being rendered inoperable by a power switch or circuit breaker, such as transmitters, HVAC systems, etc., is affected by this rule. Equipment connected to a power source by a cord with an electrical connector plugged into a wall outlet or electrical strip is not subject to the OSHA lockout/tagout rule. These rules are extremely important and increasingly subject to active enforcement by OSHA inspectors. Stations have an affirmative obligation to ensure that theirprocedures are thorough, that the tagout signs can be securely attached, and that all personnel working in the vicinity of such equipment know that the tags are to be removed ONLY by the person who affixed them. Stations must be vigilant in training all new employees and retraining existing staff anytime they have reason to believe that an employee's knowledge of the lockout/tagout policies may be inadequate.

The National Association of Broadcasters has available a 9" x 12" metal sign that complies with the tagout requirements specified by OSHA. It comes with a copy of the OSHA rules themselves, as well as a summary of the rules. It is available from NAB Services, item #4047. NPR Member Stations may order these at the NAB member rate of $40 by calling 202.429.5373 and identifying your station as a member of NPR.

HTML As An Internal Resource

Hypertext Transfer Protocol (HTTP) sites now abound on the Internet, including National Public Radio's site as well as several dozen member stations sites. The linking available on HTML (Hypertext Markup Language) documents is a powerful information sharing resource. In addition to the "homepages" NPR provides for listeners, Norb Gallery, the Audio Engineering Division's Master Control Technical Director, recently seized upon converting the volumes of hardcopy and text-only Master Control "Help" documents, explaining in detail numerous operating procedures to HTML. Now, any computer on the NPR Information Services network can rapidly scan information on hundreds of locations worldwide for audio interconnection paths, details on microphone recording techniques, a glossary of engineering terms, and many other topics. In response to requests from NPR member stations about seeing a sample of this impressive effort Norb and Rich Rarey, All Things Considered Technical Director, condensed much of the HTML documents into a version that can be accessed and transferred across the Internet. If you would like to have access to this password-protected file for either Macintosh or Windows, send an e-mail message to rrarey@npr.org requesting access to "AED Help". After confirming your employment status at a current NPR member station, he will send you a file with a password and detailed information on retrieving the file. We welcome examples of how you are using HTML internally at stations.
(Since this item was published, EUonline has made it easy to download the AEDHelp files -ed.)

NPR Urges Commission To Foster, Not Inhibit, ISDN Deployment

NPR recently filed comments with the Federal Communications Commission (FCC) detailing the network's favorable experiences with ISDN usage for improved audio quality. NPR's comments were filed in response to the FCC's Notice of Proposed Rulemaking (NPRM) regarding End User Common Line Charges which was launched on May 30, 1995. The FCC initiated the NPRM after affirming a ruling which, adhering to longstanding precedents, identified each channel in a multichannel circuit as subject to a separate subscriber line charge (SLC).

NYNEX and Bell Atlantic, among others, protested the adverse impact this rule would have on fostering further ISDN deployment, since, conceivably, each B channel and D channel would be separately assessed a subscriber line charge. NPR told the Commission that since 1991 when the network first began regular use of Switched 56 service, the number of sites regularly communicated with has skyrocketed from a dozen to over 300. Moreover, for listeners to NPR programs, the availability of ISDN quality service has meant the sounds of distant wars, and the subleties of distant spokespeople, have come to life in America's living rooms and cars.

NPR, among others, questioned the FCC's belief that applying the SLC "per facility" rather than per carrier would require higher Common Carrier Line Charges (CCLC) to offset "lost" revenues. A joint filing by several technology and telephone associations stated "[N]etwork usage will not remain constant if ISDN is deployed. Rather, ISDN will grow the pie - increasing total minutes of use, and, thereby, decreasing per minute CCLC charges." For a copy of NPR's filing, contact Assistant General Counsel Greg Lewis at 800.235.1212 extension 2450.

Fluke Meter Recall Notice (By Permission)

Fluke has become aware of a product malfunction in certain Fluke digital multimeters (DMM). This problem is the result of a manufacturing change implemented in July 1994. Only seven models are affected: the Fluke Series II Models 21; 23; KIT 23; 70; 73;75; and 77 meters imprinted on the case bottom with serial numbers between 60990000 and 63752000. No other Fluke instruments are affected. If the S/N of your DMM is preceded by a "9" or followed by an "R", this notice does not apply.

The malfunction may occur when a voltage input greater than 400 Vdc is applied in either voltage functions, AC or DC. The meter may go into a lock-up state and will indicate a reading of (or near) zero volts.

WHEN THE MALFUNCTION OCCURS, THE METER MAY NOT INDICATE THAT HIGH VOLTAGE IS PRESENT, PLACING THE USER IN A POTENTIALLY HAZARDOUS SITUATION.

The failure mode commonly occurs when the positive lead (red) is first connected to a high voltage supply and then the common (black) lead is connected.

To correct this problem, Fluke will modify your meter without charge. Even if you normally do not use your meter in the voltage range mentioned, it is recommended that you return your meter for modification.

If you are not the primary user of the affected Fluke DMM, please make every effort to pass this notice to the appropriate people within your organization.

Please send your meter to your Fluke Service Center to have this modification completed. Your unit will be modified, and on its way back to you within a few days.

At Fluke Corporation, we are continuing to work toward the highest possible level of product safety, reliability, and customer satisfaction. We want you to be thoroughly satisfied with your Fluke product. We apologize for any inconvenience caused by this safety notice, but we urge you to have the modification made as soon as possible.

If you have additional questions, please call our Technical Support Group toll free at 1.800.447.7940.

Richard W. Van Saun, Senior Vice President, Service Tools Division General Manager

Your Name; Company Name; Street Address; Mail Stop; City; State; Zip Code; Telephone Number; Model Number; and Serial Number.

NPR Studios Now Available As System Wide Resource

It seems like yesterday when NPR embarked on a comprehensive facilities design process, but it was actually only 1990. The good fortune of a new headquarters building surfaced two years later, just in time for what was being planned as a renovation-in-place to ratchet up to a completely new technical plant. Long before the first solder flowed, before the first connection was crimped, long before the blur of many nights on AutoCad®, thousands of hours of deliberations about the new plant were held. Through earnest and lively discussions, NPR staff debated what worked well and should be replicated in the new plant and what absolutely must be improved on. Probably no facility is perfect, but we are awfully proud of what dozens of team members contributed to the superbly designed and appointed 635 Massachusetts Avenue.

Each day millions of listeners through our hundreds of member stations hear the results of those efforts. What you don't hear is the silence, from better acoustics and less electronic noise throughout the facilities, lowered "operating" temperatures. No longer does the heat rise unnecessarily due to technical and production staff with no place to sit all crammed together in closet-sized record centrals. No longer do directors, call screeners, and producers share the same control room as the engineers. No longer must volumes be cranked to the max to hear subtle colorations in the production mix. Yes, we're proud of NPR's ultra flexible, purpose-built radio production studios. And we would be proud to share them with anyone with the need to produce high caliber audio production. The new headquarters was designed to be a system wide resource for public radio production and distribution. Now that the facilities have been thoroughly tested by a year's worth of on-air operations, we are ready to open the doors to outside clients.

The truth is, it wasn't just 1990, but actually 1971, as the network first went on the air, that a music recording studio was dreamed about and "imagineered." Studio 4A, with 24-track digital and analog capability and one of the largest and quietest recording stages on the east coast, is the "crown jewel" of technical facilities.

USA Digital Demonstrates Mobile IBOC AM & FM Systems

NAB '95 in Las Vegas unveiled the first public mobile demonstrations of USA Digital's In-Band On-Channel (IBOC) FM and AM systems. The FM demonstration operated with an effective data rate of 384 kb/s of which 256 kb/s were allocated for the stereo 20 Hz-20 kHz audio channel and an additional 64 kb/s were reserved for ancillary data uses. The remainder of the bit stream was used for error correction and control overhead. The digital transmitter's output of 300 watts was combined with the output of the existing KUNV-FM Harris FM-10K transmitter operating on 91.5 MHz (Figure 1). USA Digital officials indicated that low level combining was not utilized because it required linearity for digital system operation which is not present in most FM transmitters.

The demonstration utilized a home receiver, which exacerbated the analog multipath effects along the assigned route. No multipath was observed on the digital signal so long as the shuttle bus was moving. Although the system appeared to rely on an element of time diversity to combat nulls in the received signal strength (delay time was on the order of roughly 3.5 seconds), USADR indicated only coding delay was present. Several observers noted that although mobile performance was quite impressive, the signal on some routes collapsed when the bus was stopped at a multipath null (the stoplight in front of the Las Vegas Hilton being a predictable null location). Frequency response became severely restricted (perhaps only 3-5 kHz audio quality) and the signal quality was significantly distorted. Switching to the analog signal at these points showed that the analog FM signal was unintelligible.

Many engineers expected the IBOC signal to affect SCA operations, but KUNV-FM officials who operate a 67 kHz foreign language SCA service indicated there was no noticeable degradation to the subcarrier operations.

The AM system operating on a special 1660 10-kw channel was also quite impressive (Figure 2). The AM signal was in stereo, and had good upper frequency response, but was marred by "phasing" or "flanging" artifacts. The data rate for the AM IBOC system was 128 kB/s total with 96 kB/s allocated for the stereo audio signal. Quality achieved compared to the AM analog signal was excellent - a much greater improvement over the conventional analog signal than what the FM system achieved.

In a related development, FCC Chairman Reed Hundt, in response to a question concerning "radio issues" from the floor of the Chairman's Breakfast session, disclosed that the Commission may move forward with a NPRM that would permit deployment of the IBOC system within the "next couple of months." Persistent rumors within the industry indicate that the USA Digital system may be deployed in the near future on several stations in top rated markets. An agreement with National Semiconductor has reportedly been reached to mass produce the receiver chipset for integration by receiver manufacturers.

Despite the impressive progress demonstrated by USA Digital in developing this revolutionary "overlay" technique, a thorough review of the details of the forthcoming Digital Audio Radio Systems lab and field test reports will yield important data on the strengths and weaknesses of each proponent system. The report is now scheduled to be released in early 1996.

Commission Reconsiders Subscriber Line Charges' Impact On ISDN Deployment

The FCC will shortly begin a proceeding to consider changing its rules for applying the federal Subscriber Line Charge (SLC) to ISDN services. The SLC is a flat fee paid on each month's telephone bill, in addition to the local rates reviewed by state regulators. For residential users, the SLC is $3.50 per month. Local loop costs are recovered through charges levied at both state and federal levels, with approximately 25 percent collected via federal charges. Until 1984, long distance customers paid the federal costs in their interstate long distance phone bills. These costs weren't separated out, so the customer was generally unaware of their existence.

In 1984, after receiving recommendations from a committee of federal and state telecommunications regulators (known as the Joint Board), the Commission began implementation of a new rule. Under this rule, the federal costs of the loop have been collected through the SLC levied directly on end users, and a Common Carrier Line Charge included in interstate long distance rates.

The SLC is capped at $3.50 for each regular residential phone line and $6.00 for each line for multi-line business customers.

In 1992, NYNEX submitted an amendment to its tariff at the FCC. Under this tariff, NYNEX proposed to reduce its SLC for certain services taken by large business customers. These services, including primary rate ISDN service, employed advanced technologies permitting a single facility to deliver up to 24 channels to a single customer. While NYNEX had previously charged a multi-line business SLC of $6 for each channel, for a maximum of $144 per month in federal charges, it proposed in its amended tariff to charge $6 in SLCs for the entire facility, or 25 cents per channel.

The NYNEX tariff was rejected by an Order of the FCC's Common Carrier Bureau in November 1992 (DA 92-1622), finding that the 1984 rule applied the SLC to each derived channel and not to each facility.

NYNEX and Bell Atlantic petitioned for reconsideration of the Bureau's NYNEX decision. The petitions argued that the Bureau had incorrectly interpreted the SLC rule. In January 1995, the full Commission upheld the Common Carrier Bureau's interpretation of the SLC rule. At the same time, the Commission noted that this decision raised policy issues that would be best addressed in a rulemaking proceeding after full development of a record reflecting the views of all interested parties. The Commission is very sensitive to public policy ramifications on emerging technologies, such as ISDN, and will develop a full record carefully examining how to apply SLCs to ISDN in a rulemaking petition expected in the next few weeks.

Back-up STL Type Authorization Relaxation

The FCC has agreed to continue to allow the use of unapproved 944-952 MHz transmitters for back-up purposes only. Stations whose equipment was unable to meet the frequency tolerance requirements under the type authorization rules (Subpart J of Part 2 of the Commission's Rules) by July 1, 1993, are now permitted to keep such equipment in operation for hot-standby or other back-up purposes. The Commission stated, "Equipment which has not been type approved under the equipment authorization program and which was in service prior to July 1, 1993, may be retained solely for temporary uses necessary to restore or maintain regular service provided by approved equipment, because the main or primary unit has failed or requires servicing. Such temporary uses may not interfere with or impede the establishment of other aural broadcast auxiliary links, and may not occur during more than 720 cumulative hours per year. . .All unapproved equipment retained for temporary use must have been in the possession of the licensee prior to July 1, 1993, and may not be obtained from other sources."

EBS Equipment Revisions

"This is a test of the Emergency Broadcast System (EBS)" Soon we will no longer hear those words. The present EBS system is being replaced over the next two years by what is described by the FCC as the emergency warning system of the 21st century. This digital system will work with both new and established communications technologies, including satellite, broadcast, and cable, to make the disaster warning system more effective. The new system emphasizes speed, reliability, and efficiency.

The FCC has established the following time table for the four step process of modernization, technical changes, and operational changes to the current EBS. The fourth change to the system will be changing the name from EBS to EAS (Emergency Alert System) to symbolize the new multisource emergency communications approach and move away from negative stereo-types associated with EBS.

Modify existing two-tone decoders (change decoding time from 8-16 to 3-4 seconds).

Allow existing two-tone signal to be transmitted for 8-25 seconds using two-tone encoders.

Require AM, FM, and TV stations to install digital EAS (monthly test of digital codes, two-tone signal, audio/video message and weekly EOM; weekly test of digital codes only).

Require cable systems to install EAS digital encoders and decoders (transmit EAS codes, two-tone signal, audio message and video interruption on all channels; video message on one channel).

We are fast approaching the July 1, 1995, date when stations may transmit the shortened two-tone attention signal for not less than 8 seconds nor more than 25 seconds. All EBS tone decoders should have been modified prior to this date (FCC modification date was November 10, 1994) to detect the shorter 8 second alert signal. There has been a flurry of calls to the manufacturers of EBS equipment for the modification information. In an attempt to assist NPR member stations, following is a short compilation of information gathered by Mr. Dave Biondi of Houston, Texas. The information provided should allow any person to successfully complete the modifications to the unit.

To assist you in converting your present EBS equipment to the new 8 second standard, I have accumulated the technical modifications to Gorman-Redlich, TFT, and McMartin type EBS Encoder/Decoders.

The outputs of the 107 Hz filters for the two tone decoders go into a diode, a parallel R/C circuit, and another diode, and then combine into a voltage divider. Where these two diodes tie together, there is a 47 uF Tantalum capacitor. Change this to a lesser value that will result in an un-mute time of 3 to 4 seconds. (Try starting at 22 uF.)

On the encoder, turn the 1 megohm "Activate Internal Adjust" pot counter clockwise until the tone is at 9 - 10 seconds (recommended). This modification may require a slightly longer closure of the activate switch to allow the 47 uF timing capacitor to fully charge.

On the decoder board, replace C13 with a 22 uF 25 volt Tantalum capacitor. Replace R26 with a 182K ohm 1/4 watt 1% resistor. This should cause the decoder to activate in 4 seconds.

On the encoder board, cut the trace at Z3 pin 1. Then jumper to Z4 pin 9. This will give 8.5 - 9 seconds of encode tone.

If you want to put a 8.5/23 second select switch in, install a SPDT switch on the back panel of the chassis with the common on Z3 pin 1 and the other switch terminals on pin 9 and 11, respectively, to select the tone times.

In the EBS-2 Decoder, parallel R37 with another resistor which will result in a un-mute time of 3 to 4 seconds. Try starting with a 560 K ohm 1/4 watt 1% resistor.

In the TG-2 Encoder, adjust the trimpot near the NE555 chip clockwise to 9 seconds.

The manufacturers I contacted to get this information all expressed their frustration at the inundation of phone calls they had received for the mods. I guess they haven't got much else done but answer modification questions. You can help by passing this information around to others in your broadcast community.

The preceding information was printed with permission of Dave Biondi at The Broadcast Service Company, Houston, Texas. Mr. Biondi's information has addressed the most popular EBS units in the market place. There are three other units covered by the following information.

There are three units, the 1000, 3000 and 3000-C - all require the changing of the processor chip within the unit. The chip is available from Broadcasters General Store or directly from MTS.

This unit simply requires resetting the rear panel accessible trim pots. There are two pots, one controlling encoder timing and the second the decodering timing.

Sony TCD-D7 Product review

Late in 1993, NPR purchased a Sony TCD-D7 DAT Walkman and a number of available accessories for evaluation. The D7 was being considered as a supplement to, and a possible replacement for, the fleet of analog cassette recorders used in the daily gathering of news and events programming broadcast on NPR. Upon initial testing and trial runs, the D7 operated both electronically and mechanically quite well. Initially there was a degree of apprehension due to the D7's compact size and mechanical complexity, but after disassembling the D7, this fear has passed. Because of NPR's new building project in early 1994, the D7 project was postponed for several months.

In September of 1994, following additional trials of the D7 by several reporters and technicians, NPR made the decision to purchase a group of the units for field use. Presently, there are 10 units permanently assigned to NPR reporters, and an additional 15 units have been placed in the Quartermaster's equipment pool for general assignment to technicians, reporters, and producers. Of the ten D7s assigned to reporters, all are located at various NPR Bureaus worldwide.

Powering the D7: The operation of the D7 has to be portable and not tied to a source of AC power. Under ideal conditions, the D7 can run about three hours on a new set of AA alkaline cells. This proved to be a problem; in initial field tests run time was usually less than three hours. The solution was to construct an external battery pack for long gigs as has been done for other battery-powered devices in the NPR portable fleet. The external battery pack is a four D cell holder. NPR chose alkaline D cells because of their universal availability and ease of use. Operation from the external D cell pack has provided in excess of 24 hours of recording time on a set of fresh alkaline cells. The battery pack is the type that places the batteries side-by-side, not two-in-series on each side. NPR had obtained holders of the two-in-series type, and found the fit of the batteries in the holder was so tight that the cells would be held away from the terminal contacts at the end of the holder and not supply power to the machine.

The next problem was to locate a coaxial power connector to fit the DC jack in the rear of the D7. Sony specifies this jack as a standard 3.5 mm fitting. We obtained connectors of this size from several vendors. Of those connectors, none performed satisfactorily, some did not fit, one would break the connection when moved, all failed. The only connector that worked reliably is from Sony. Unfortunately, at the time of initial deployment of the D7s, we were unable to locate the Sony connector as a separate part. So, purchase a D7 power accessory from Sony, and cut the connector and cable off the adapter. The adapter used was the Car Battery Cord Sony P/N DCC-E160L or DCC-E260HG. This device provided us with a right angle molded connector and cable. About two and one-half (2.5) feet of cable was left attached to the coaxial connector, the other end of the cable being attached to the battery pack. The cable was strain relieved at the battery pack with two nylon ty-wraps.

Continuing the search for power connectors and battery packs, the following Sony items have been obtained. The J2501034A DC Power Cord has the correct plug to fit the D7 power jack (non-right angle plug). This cable is 42 inches long and can be used for a battery pack or other power adapter. The Sony EPB-IPS36 Battery Case is a four D cell pack with the correct right angle power plug to fit the D7. It also has a belt clip. This battery pack is actually made as an accessory for a Global Positioning device Sony markets. The cost of the two accessories are $2.50 and $28.00 respectively. If you purchase the power cable and the battery holder we used at NPR, you can fabricate the D cell pack for about $5.00.

When using the external DC input on the D7, there are a number of power conservation circuits that are bypassed. It was found that the D7 will draw about 200 milliamperes constantly when externally powered. If left connected, this power draw will discharge the D cell pack in three to four days. A decision had to be made whether to train the persons using the D7 to connect the D cell pack only when using the machine or modify the D7s. It was decided the problem had to be solved electronically and not in the method the machine was used.

A note of caution here, if you are not familiar with and do not have the equipment to work on surface technology boards, you may cause permanent damage to the D7. Several possible solutions to this problem were considered. One was to put another connector in the D7 to supply power directly to the same point as does its internal battery pack. Due to the dense packaging of the D7 and the confusion of a second external power connector, this was not deemed wise. It was suggested that we use a dummy battery holder in the D7 with a wire running to the external battery pack. This would mean making a hole somewhere in the battery compartment for the wire to exit. It would also mean that if the user needed to quickly place the recorder in their pocket and take off after an interview they would have to take the D7 out of its case, remove the dummy battery holder, and install the AA cells and holder.

NPR did not feel this was an acceptable option, because in doing so the user would completely remove power from the machine and lose timing information. Fumbling with the batteries in a fast moving situation would definitely cause a disaster. After studying the service manual, NPR observed that the internal batteries and the external power source are tied together by a steering diode and that the internal batteries are disconnected from the circuit by the power input connector. There are three things connected to the external power connector that are separated from the internal batteries by the steering diode. One is a circuit that generates a reset pulse for the microprocessor when an external power source is connected or disconnected. Another is a voltage regulator that provides power for the remote control circuitry through the digital in/out connector. This is also connected through steering diodes to a voltage that is supplied from the control PCB. The third is a transistor that serves to bring a pin on the microprocessor low when the external power source is connected. It was decided that we could safely remove the voltage regulator since it is a duplication of existing circuitry. We removed transistor Q515 and the 2.2KW resistor connected between the base of the transistor and ground. We also removed Q505 that tells the microprocessor it is connected to an external power source.

After modification, the D7 behaves as if it is always on internal battery power and will therefore go into standby mode when it sits idle thus conserving power. It also allows the battery indicator to function permitting the operator to observe the condition of the external battery. With these modifications made, the D7 draws 3 milliamperes from the external power source in Low Power Mode. Over a two week period, NPR obtained 24 hours of record time and 5 hours of playback time with the external battery pack connected continuously. The D7 had not completely shut down at this point, but the low battery indicator was flashing to alert the user to change the batteries. In an emergency, the external power connector could be pulled and there would still be a couple of hours of use available on the internal batteries, assuming they had been kept fresh. At this rate of consumption, the cost of the Car Battery Cord that was used for the connector is recovered in about two months use. Table I is a listing of NPR's measured power consumption of the D7.

Microphone Inputs: In most situations, the D7 will be used by NPR reporters in gathering voice tracks. It was decided to fabricate a special D7 Microphone Input Cable. A note of caution, some non-Sony mini connectors do not fit the D7 jacks and it is possible to get a plug stuck in the D7 jack. The mic cable we have settled on splits the mic signal to drive both left and right channels with the right channel attenuated -10 db. Virtually all recordings are mono voice. The normal recording configuration of the D7 is:

NPR uses the Beyer M58 and EV RE50 microphones. These settings will provide good gain control range.

Line Inputs: The line inputs of the D7 are designed to operate in the -10 consumer environment. When operating in the + 4 world, the D7 input amplifier (before the input gain control) can be over-driven. Once again, NPR made a line input cable. The left channel is attenuated -10 db and the right -20 db. Both channels are driven from a mono source. This cable will put the input gain control in the middle of its range. It is very common for an NPR reporter to attend a press conference and plug the D7 into a "Mult" box that will supply a +4 level. Each of the input cables is labeled at the XLR connector end as to its specific use, either "Sony D7 Mic Cable" or "Sony D7 Line Input Cable". The following Figure I and II represent the wiring and pad detail for the D7 Line and Mic cables.

Field Carrying Case: Packaging of the D7 for field use was quite easy. Due to its small size, we chose "off-the-shelf" camera bags for this purpose. Two basic bag types, the Tamrac 704 and 705 are being used. The 704 is a rectangular shaped bag that can be carried over the shoulder or as a hip pack. This bag is used most often by the reporters. The Tamrac 705 is a triangular shaped hip pack. This bag is typically taken into the field by technicians and will allow them to carry other equipment in addition to the D7. There is also a Tamrac 603 bag (same size as 704) that has a very nice oversize top flap that will cover the top flap zipper when closed and protect the contents of the bag from a harsh environment. This will allow you to keep the bag closed and route the mic cable under the flap and operate during inclement weather. Figure III is a side view of the D7 and associated equipment in the Tamrac bag. The "case divider" is two bag dividers that are supplied as part of the Tamrac bag and are held in place by existing Velcro.

D7 Accessories: The D7 has a group of accessories available. The first to consider is the AC Power Adapter. There are two available, the ACE-60HG for 120 VAC or the ACE-60AM for 120-240 VAC 50/60 HZ. Because NPR reporters frequently travel in Europe and countries other than the United States, we standardized on the ACE-60AM because it functions both on US and European power sources without the need for setting switches or external transformers. The following description of four adapters was taken from the Sony literature.

RK-G129HG, is a mini stereo plug to two (left and right) phono plugs cable. This cable will allow easy connection of the D7 to inputs and outputs of other consumer type stereo equipment.

RAK-DA10, Digital Connecting cable, (phono plug to 7-pin I/O connector). This cable will allow connecting the D7 via its 7-pin jack to the coaxial output (Sony/Phillips system) of a CD player or other DAT machines output if equipped with a coaxial output. This is a coaxial digital (SPDIF) input connection to the D7.

POC-DA12, Digital Connecting cable (Rectangular-shaped optical digital input/output plug to 7-pin I/O connector). This will allow connecting the D7 to a similarly equipped CD player, DAT machine or digital amplifier.

RMT-D7 (1), Remote Digital Commander, this device connects to the 7-pin I/O connector of the D7 and allows wired extended control of the following functions.

· Perform both normal speed and high speed cue/review with the double-function FF/REW buttons

RM-D3K, System Adapter Kit, is a two unit kit supplied with the RMR-D3 Part 1, Remote Control/Timer/Digital I/O adaptor (requires AC power and the D7 to be externally powered). Part two, RMT-D3, hand-held infrared remote control. The RMR-D3 connects to the D7 via 7-pin I/O connector. It provides either coaxial or optical SPDIF I/O access to the D7 (there are no coaxial or optical cables provided). The RMT-D3 hand-held remote has controls for all transport functions, direct entry of edit, start IDs and Program numbers, counter modes, and CD player functions.

Reliability So Far: To date, NPR has lost a couple of recordings using the D7. The problem was a threading malfunction of the D7. The rule is to run a test recording and then not remove the tape from the D7.

The first damaged machine was returned during the first quarter of '95. The machine had broken loading gears which were easily repaired. It should be noted that this machine had been in the field for 15 months.

NPR has used D7s in Haiti, numerous trips to Europe, Africa, Asia, and all across the US. The reporters and technicians all seem to be very happy with the results. In an effort to simulate hot, humid situations that will be encountered in the production of the forthcoming National Geographics Series, we have tested the D7 and various accessories at the National Zoo's Rain Forest Amazonia Exhibit. This exhibit operates at a constant 85 degrees F and 85% humidity. The equipment was placed in the exhibit without moisture protection in an open carry-all bag. The D7 was left running in record loaded with a two hour tape. After two hours of recording, the D7 rewound and shut itself off. When the engineer returned seven hours later, the D7 was again placed in the record mode and all the microphones that were with it were tested. All equipment powered up and functioned satisfactorily. The D7 seemed to be unaffected by the conditions and continued to record and play normally. The gear was only exposed for seven hours. Your experiences may vary, especially when going from air conditioning to hot and humid conditions.

The D7 does have moisture sensing circuitry. In the event moisture does form on the inside of the machine, the "Moisture Condensation indicator" will appear in the display between the battery level and audio level meters. Silica Gel packs are recommended inside the bag when such conditions are expected. NPR recently completed the first segment of the National Geographic specials in Panama. Three D7s were used as the primary recording machines and all produced satisfactory results.

Specifications: The following are performance measurements conducted by NPR on the Sony TCD-D7. Our goal was to measure the analog performance of the D7 and to show that use of the NPR fabricated cables does not degrade these basic performance numbers. Graphs I - IV are two sets of measurements. Set one are line input to line output measurements. Graphs V - VIII are mic input to line output measurements. With the exception of Graphs IV and VIII, all connections between the test equipment and the D7 under test were direct connections with no intervening pads. Graphs IV and VIII are frequency response and loss measurements on the NPR-produced Line and Mic input cables described in this report. Graph IV (a) is the frequency response plot of the left (top trace) and right (lower trace) line input channels to line output of the D7 utilizing the NPR Line Input Cable. The graph shows two results: the frequency response of the basic cable is flat to within a db, and the right channel is attenuated 10 db below the left channel. Graph IV (b) is a repeat measurement of IV (a) with 100' of cable introduced into the measurement and plotted over IV (a). Graphs VIII (a) and (b) demonstrate the performance of the NPR produced Mic Input Cable.

Conclusion: With over 25 TCD-D7s, NPR is dedicated to their use. NPR does not expect the D7 to be as robust mechanically as previous technology, but this is the trade off when using consumer equipment. NPR is very pleased with the sonic performance of the D7. Discounting the variation in microphone techniques of the persons using the D7, the quality of the audio has been very good. We prefer linear digital recording through the production process to eliminate the possibilities of trans-coding errors that may arise when mixing a variety of digital compression algorithms. The D7 fits this need affordably. NPR has sent reporters on assignments to Europe carrying nothing more than a single D7, mic, and headphones. They have returned with excellent quality audio. We have faith in the technology and hope to continue adding more machines to the fleet.

The NPR Engineering Services Unit is set-up to maintain the D7s. A number of parts for the D7 have been placed in stock based on experience with other Sony portable products. Complete schematics with parts listings are on file, and the specialized equipment to service surface mount technology is available. Based on high audio quality demands, size, low power consumption, and the ease of use, the D7 has succeeded in meeting NPR's needs at an affordable price.

I would like to thank Bob Butcher, Bill Hineman and Dennis Byrnes of NPR's Engineering Services unit for their assistance in the measurements, modifications, and maintenance on the D7 machines. Without their assistance, we would not have the data and information contained in this article, and NPR would not have attained the high level of proficiency of use with the D7. Bill Deputy of NPR's Technical Production Unit performed the tests at the National Zoo.

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