Radio World: InoMini 632 - Pro Features, Reasonable Price

(this article appeared in the July 25, 2012 edition of Radio World)

The 632 in action, tuned to KCBX-HD3 while
installed on Broadcast Peak.

In May of 2010, the FCC codified an informal policy of allowing analog FM translators to rebroadcast an HD Radio multicast feed, thus bringing that programming to a (theoretically) wider audience. For many operators, this was a golden opportunity to allow greater localization to their markets via translators. For critics, it breaks some rules by effectively allowing translators to originate unique programming without counting towards the market ownership caps.
  

Either way, if a translator owner wanted to relay an HD2 or HD3 or HD-whatever station, using over-the-air reception, they had limited options: use a consumer-model receiver, trying to modify it or otherwise working around its lack of professional features; or spend a lot of money on a professional diagnostic model that might be overkill for the purpose.

Enter the Inovonics InoMini 632. Building on a tradition of “pro” Inovonics receivers often used for OTA reception and relay, the 632 is a solid choice for that purpose. Even though it’s technically sold as a confidence monitor, meant to be used in a studio with lots of clean signal, it works well in remote applications, as I discovered.
 

Rear panel of the 632.

PROFESSIONAL
The 632 is a compact, 1RU tall, 1/3-rack width box. The front has a multifunction display, controller knob with push-to-select, and a 1/8-inch headphone jack. The back has three male XLR connections: left and right balanced analog out, plus AES digital out. There’s a female F connector for RF in, a four-connector Phoenix block for status out and a pair of power jacks; the 632 is designed to be able to daisy-chain one power supply for multiple units in one rack. 
  
The status outputs are HD loss, audio loss, signal loss and ground. HD loss is when the DQ (Digital Quotient — an iBiquity measurement of several factors inside the codec) meter drops to zero. Audio loss is determined by a user-adjustable silence sensor (1–120 seconds), and signal loss is by a user-adjustable hash mark on the RSSI (received signal strength indicator) meter. I typically set the hash mark one bar below the seemingly-most-stable signal level on the RSSI.
  
On the bench the 632 demonstrated the usual solid receiver performance that most HD Radio receivers have; the inherently low signal levels of HD (running from 1 to 10 percent analog power) demand quality receivers. It was comparable to my Boston Acoustics Receptor HD I had hooked up to the same antenna via a splitter. 
  
I noticed that the brick-style power supply put out a surprising amount of noise on the FM band. I suspect it’s partly because it has hefty capacity to handle up to three 632s via the aforementioned daisy-chain method. A lower-amperage wallwart I had handy produced no audible noise effects. I don't consider the noisy power source a deal-killer; in the field, a receive antenna would normally be more than far enough away to avoid any RF interference from the power supply.

For field testing, I elected for a challenge: reliably receive KCBX-HD3 up on Broadcast Peak, a 4,100-foot mountain about 20 miles northwest of Santa Barbara, Calif. 
  

KCBX's coverage map.
Broadcast Peak is located near
Solvang in the lower right.

KCBX is a Class B FM that’s 70 miles NNW on Cuesta Peak near San Luis Obispo, a hefty distance for a 5,300 watt ERP analog signal. Reduce that ERP to –14 dBc, and then add in several grandfathered high-power “Super B” stations on Broadcast Peak (34 kW, 108 kW, etc.) and a known, consistent tropo path over the Pacific Ocean from San Diego, coupled with daily external temperature swings from mid-50s to mid-80s, and you’ve got a challenge!
  
I had two medium-sized Scala yagi FM antennas at my disposal. One was in the compound, and thus subject to more interference from nearby stations, but it had better filtering (bandpass, with a notch to reduce a physically nearby translator on 90.9FM) and a short coaxial cable feed. The other was several hundred feet away horizontally, and several dozen feet vertically, mounted on the north side of the mountain. 

The location reduced interference issues (only a bandpass filter here) and eliminated the San Diego tropo path problem, but added a lot of cable loss. Normally it needs a preamp located at the receive antenna. We used an Advanced Receiver Research gallium-arsenide FET preamp that’s wideband, very clean, and adds about +20 dB of signal. But at first I took the preamp out since they often raise the noise floor enough to swamp the inherently low-powered HD carriers.
  
Using the first antenna, the “compound” antenna, the signal seemed OK at first, but quickly developed significant dropout-to-silence problems. The 632’s RSSI read about 40 of 48 bars, but during silence the telemetry outputs indicated “HD loss,” implying that the RSSI was adequate, but a high noise floor was too much for a weak HD signal. 
  
I switched to the “down the hill” antenna, sans preamp, and there was less silence but still dropouts. The RSSI was 30 of 48. During silence the telemetry read “signal loss” before the “HD loss” appeared, indicating the signal was clean but just too weak. Finally, I put the preamp back into the circuit. That seemed to do the trick! RSSI jumped to 47 of 48 bars, and reception of HD3 was suddenly rock-solid.

PERSPECTIVE

To put this in perspective, at one point I hooked up a Sony XDR-F1HD, often considered the modern-day "gold-standard" for receivers, to the same antenna systems but without the external filters and preamps. The Sony could easily pick up several distant stations that the 632 could not in that situation. 
  
So is the Sony receiver “better?” Not necessarily! The Sony lacks the ability to lock to a specific HD multicast and it won’t hold its settings through a signal loss or power outage. The 632 will do all those things ... which are mighty important for limited-access facilities like mountaintops ... and it performs nearly as well as the Sony if you add the external filters/preamps.
  

The author on Santa Ynez Peak, CA, with Broadcast Peak
about a mile in the background.

There are some features I wish the 632 had, namely a composite output and actual remote control instead of just status outputs. However, such features would add to the cost and are, strictly speaking, not necessary. Doubly so on what’s designed to be an in-studio confidence monitor.
  

In the end, if you’re looking at using over-the-air reception of an HD signal to feed any destination, be it another transmitter or just a confidence monitor, the 632 is an excellent choice. It’s small, rugged and a pretty good receiver. Challenging reception situations may require investment in more professional antennas and filters, but for serious applications such things are recommended anyways. 
  
Most important, the feature set finally delivers what many broadcasters have been wanting for some time and does it without breaking the bank.
  
Aaron Read, CBT, is the new IT/Engineering director for Rhode Island Public Radio.