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Field Report: Deva Broadcast DB44
Deva Broadcast's newest entry into the FM monitoring arena is the DB44 compact FM radio monitoring receiver. It's an IP-accessible, DSP-based analog FM monitoring (no HD Radio) receiver that packs a lot of capability into a small package. The physical unit is an almost pocket-sized device with connections on the rear for 12Vdc power, an FM antenna, an RJ-45 for the network connection, and a high-density DB-15 for an external cellular (GSM) modem. On the front panel there are three LEDs for power, LAN connection and for the GSM modem, and a 1/8" headphone jack for local audio monitoring. A 1RU mount is also available.
An obvious application for this device is to provide remote monitoring at FM transmitting sites. It also might be a good fit for remote broadcast or vehicle applications. The device can be set to monitor up to six FM preset frequencies and send email or SNMP alerts on up to six parameters on each preset: RF level, MPX deviation, left and right audio level, pilot and RDS deviation.
The DB44 is an embedded device; there is no hard drive or display. Boot time is in seconds and it's ready to monitor immediately. It is operated entirely through an IP connection using either a dedicated or DHCP address, and has a well designed embedded website for monitoring and control functions. Web pages are arranged as an intuitive tabbed display. The main page shows meters for RF level, measured multipath level baseband modulation (positive and negative peaks), audio levels, pilot and RDS levels. The lower 15 percent of the DB44 page is the "dashboard" of the device. This mimics a radio display showing the frequency, status of the stereo and RDS lock, amount of internal attenuation selected, and a summary display of alarm status of all six presets. Buttons for the presets are in this dashboard as well as a blank to manually enter a frequency. The remaining items in this screen allow the selection of RDS mode (European or U.S.-standard), the local time and a listen button. The listen button engages a selectable-bit rate MP3 audio stream.
One of the devices most compelling features is that all readings, meters, settings, etc., can be accessed using a standard Web browser - even using an iPad or Android device, although. I noticed that the graphs and spectrum displays would not resolve on certain Android devices, however, but that might have more to do with the specific mobile browser I was using.
It's apparent that one of the core competencies of Deva is in RDS. The RDS page is comprehensive with a display of the scrolling RadioText (RTA and RTB), basic RDS fields and a chart of all decoded RDS groups with a percentage measurement based on the overall RBDS data stream or group count. A very useful graph on this display is a rolling RDS bit error rate (BER) display.
The remaining pages are essentially live graphs. The overall FM graph is a multi-colored plot of MPX, pilot, left and right audio levels. It's a good way to capture an average of the significant parameters of the analog signal. The MPX tab shows both baseband MPX deviation as a function of deviation in kilohertz over a percentage of time. The graph quickly shows modulation density. There's also a rolling 30-minute-average graph of baseband power measured in dBr.
|Performance at a glance|
|◊ Real-time audio program streaming
◊ Built-in oscilloscope and spectrum analyzer
◊ LAN port for TCP/IP remote control and monitoring
◊ Alarm dispatch via email and/or SMS
◊ RDS/RBDS decoder with BER meter
The spectrum analyzer tab is a unique feature: It is a baseband and audio spectrum display. Initially it shows the baseband from 0-65kHz so you can clearly see the mono signal, stereo pilot and L-R and RBDS carriers. Perhaps it's a curiosity but I like being able to quickly see the baseband in a glance. It was particularly interesting using this tool while some alternate stereo modulation techniques were being tested in town. The spectrum analyzer display can be selected for the discrete left and right audio and plotted using one of a number of waveform sampling and display models.
The scope display is essentially what it would seem: an oscilloscope display of the baseband, left right and a composite graph of the left/right audio. It is similarly intuitive with the bandscan tab. The start button on this page initiates a measurement across the FM band plotting the signal strength in dBuv. There's a moveable frequency marker to read the individual levels to 0.01dBuv resolution.
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