At no previous time in broadcast history has the need for excellent FM tuners been greater. With the build-out of the FM band, close frequency spacing and adjacent channel interference have resulted in a crowded, noisy band that challenges receivers. Ironically, until recent years, the quality of available FM receivers had been declining while the FM band itself became more crowded and noisy. Arguably the best tuner one could buy in terms of reception performance at one point was the Sony XDR-F1HD, an unassuming little $100 consumer box with astounding FM performance that was only in production for a short period of time. Good tuner options were limited to scouring eBay for these Sony tuners or vintage analog tuners.
Fortunately, all of that has changed. A new generation of tuners based on software-defined radio technology have exceeded the best vintage tuners in terms of reception performance through the use of powerful digital signal processing. These processors-as-radio-receivers put the FM/AM front ends, tuning synthesizer, channel filtering, FM multipath improvement, demodulation, FM stereo decoding, weak signal processing, noise blanking and RDS on an integrated device and have achieved amazing performance.
As the broadcast engineer for Northern Community Radio, I run a small network of two full-power FM stations (KAXE and KBXE) and two translators which rebroadcast the KAXE signal (delivered over-the-air via FM receiver) from 73 and 90 miles away respectively. In addition, I use a signal received over-the-air from 85-miles away an STL backup for KBXE. My motivation to find and use the best FM tuner is high and I had the opportunity to test the Inovonics Aaron 650 FM Rebroadcast Receiver, a feature-laden model upgrade from the base Aaron 640. Inovonics� website has an excellent model comparison chart between the two models.
Features and Operation
Composite pass-through or regeneration
The Aaron 650 operates in either composite pass-through or composite regeneration mode. Pass-through mode eliminates retransmission delay (latency); but the reception magic turns on with composite regeneration. This mode completely reconstructs your baseband signal for lower noise and allows you to alter your RDBS messaging prior to rebroadcast. The effect of cleaning up the signal is dramatic as evidenced on the very cool OLED FFT Spectrum Analyzer built into the unit as well as audio listening tests. It should be noted that the headphone output on the Aaron 650 is always outputting audio from a baseband regenerated signal, so headphone audio cannot be used as an A-B comparison when baseband regeneration is toggled on and off via the user interface. For my listening tests, I used an Inovonics INOmini 514 FM Multiplex Decoder and listened to the MPX output of the Aaron 650 as I toggled the baseband regeneration on and off. The feature made a dramatic difference in quality on weak signals. Unfortunately this function is not available on the Aaron 640 model, but in my opinion it is absolutely worth the price premium in difficult reception conditions.
Dual antenna inputs and MPX outputs
The Aaron 650 also has dual antenna inputs and composite outputs, as well as balanced analog and AES digital line outputs. Multiple antenna inputs are just the ticket for off-air receive situations where one wants to switch between independently optimized RX antennas. Station presets can be saved, and it also saves the chosen antenna input along with all other reception parameters, a nice programming feature that was not overlooked.
Streaming audio confidence monitor
Confidence monitoring of the received signal quality and preset choice can be done remotely over the streaming audio utility built into the Web GUI. This is an excellent feature that gives a choice of two streaming rates for high or low quality connections and runs with about a 5-second encoding delivery delay.
Advanced metering and spectral analysis
The most eye-catching feature is the FFT Spectrum Analyzer for the MPX, Left/Right XY plots and audio levels over time, as well as the built in BandScanner for local RF spectrum analysis. Presented on the high-resolution OLED display, the effects of baseband regeneration can be immediately seen on the recreated MPX output. The band scanner is particularly useful to see signal levels entering the antenna input from the entire FM band as this can point out possible frequencies needing attenuation with an external filter. The OLED display actually has a higher resolution than the Web GUI representation and if one pauses the cursor over a peak, the frequency is displayed. This is another useful little feature in the unit�s interface.�
Alarms, alerts, backups
The Aaron 650 is well equipped with local alarm tallies plus self-logging alarms that constantly check for Audio Loss, RF Loss and RDS Loss. Upon loss of the incoming carrier, loss of program audio or RDS �hijacking,� the off-air program may be replaced with prerecorded material on an SD card, a streaming audio feed or a secondary off-air frequency. E-mail and text notifications can be sent on these conditions, and SNMP is supported for remote monitoring and control.
With the advent of software-defined radio and DSP control comes a suite of control parameters that put vintage analog receivers to shame. There is active reception processing for bandwidth, stereo blend, HF blending and multipath mitigation. For example, within the stereo blend reception tool, the blend amount is immediately displayed. When the AUTO featured is turned off, the parameters of RSSI, USN and multipath can be selected in any combination with sliders that adjust the amount of blend based on the threshold of the selected parameter. You can listen and see the blend amount in an effective interface. Note that the web GUI is the best way to access and adjust these parameters and one can tweak the receiver while wearing a pair of headphones plugged into the front panel. The receiver includes an internal test oscillator. Frequency, output and L+R balance are adjustable � a�handy tool for setting up the outputs.
Upon receipt of the Aaron 650, the first thing I did was check the Inovonics website for a firmware upgrade. I�m pleased to report that access to the firmware is an open and direct download, without registration, authentication or waiting to be emailed the file. This is desirable for the broadcast engineer who may be working with limited time constraints or at odd hours. Additionally, the firmware upgrade process went smoothly and matched printed instructions. Boot time from a cold power up is fast, around 1 second. The single �turn and push� front-panel knob to access the sub menus functioned well and has a good intuitive logic; however the Web GUI of this unit is a nicer way to explore the receiver as it has a clear and responsive layout. The lack of a chassis fan is appreciated and I can see these receivers being bought by the hi-fi crowd for DX listening.
At our transmitter site I mounted the Aaron 650 alongside another excellent DSP radio, which served as an 85-mile over-the-air source of network audio in case our STL fails. Both were excellent on a weak receive signal. As an experiment, I padded the split antenna input until each receiver became noisy. This point occurred at an indicated 1 dBuV RSSI on both receivers and both became listenable at 4�6 dBuV. While the competing unit has far greater granularity over reception parameters such as signal attack Tc, signal release Tc, multipath attack Tc, I found that I preferred the user interface of the Aaron 650 as one could adjust reception controls with a simpler interface that allowed me to dial up the clearest reception in a shorter amount of time. With the Aaron, each simple slider move results in an instantaneous change of the reception tool and in the headphone audio. As with audio processor presets, it is important for DSP-controlled receivers to be able to run close to optimum performance with the heavy lifting already done for you as sometimes too many choices can be paralyzing. Alternative to manual adjustment, the �AUTO� mode of each reception tool has been programmed with effective algorithms and result in excellent, effortless reception.
If there is one design gripe I have, it is that in order to accomplish a hard reset to return all values to a factory default including password, a front-panel button must be pressed while simultaneously applying power to the IEC connector in the rear. This almost necessitates removal from the rack, an inconvenience for any software controlled equipment that may need a reset.
In summary, the Aaron 650 FM Rebroadcast Receiver is a winner. It provides the necessary architecture for full-featured translator use along with reception performance and IP connectivity which previous generations of equipment lack. It is nice to know that one doesn�t have to cruise eBay for that vintage Sansui 9090db receiver to get the performance you need.