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Communications Specialties Pure Digital FiberLink 7220

Powerful, simple fiber optic transmission.

Communications Specialties Pure Digital FiberLink 7220

Dec 1, 2004 12:00 PM,
By Jeff Sauer & Mark Johnson

Powerful, simple fiber optic transmission.

Fiber optics was all the rage a few years ago. It was the apparent future of all communications and just about as big a Wall Street draw as everything Internet had been at the end of the 1990s. Then, mirroring the bursting of the high-tech bubble, fiber optics had a serious cooling-off period following all that hype. Yet neither IP technology nor fiber optics has gone away. Indeed, both continue to evolve, except now manufacturers have been forced to rely on actual, saleable products rather than just that hype. And that’s to the benefit of customers.

Communications Specialties is a small player in the world of fiber optics telecommunications giants. Still, its Pure Digital FiberLink 7220 Series kit is a good example of how today’s fiber optics has grown more affordable and durable enough to reach new markets, including audiovisual installation. For prices that are at least competitive with traditional copper, Communications Specialties’ 7220-KIT proves that fiber isn’t an exclusive, intercontinental technology any more.

The 7220-KIT ($2,695) is a bundle designed to be something of an introduction to fiber. The package includes the 7220 transmitter and a 7221 receiver (both are available separately for $1,095 MSRP each), 250m of single-mode fiber optic cable, and a plethora of converter cables for connecting both audio and video sources.


The idea is simple: the 7220-KIT has everything you need to plug in a source, connect to a remote monitor, and go. To get a monitor up and running, it’s as easy as making any other direct cable connection. The only difference is that the signal is traveling a 250m distance without any fine-tuning, any other repeating or signal processing, or any calibration. That simplicity alone might be enough of a surprise to entice newcomers to take a look, especially those for whom fiber has been somehow inaccessible or shrouded in mystery. It certainly made our job of testing the kit quite easy. We plugged it in, turned it on, and it worked.

Specifically, we connected both video and audio sources to the 7220-KIT and ran the signals through the 250m of fiber, and we neither saw nor heard any discernable difference in quality on the other end. We used an Extron VTG-400D pattern generator, as well as test footage from a variety of sources, including Silicon Optix benchmark DVD, to evaluate video quality. And for audio, we used our ears on familiar source material, as well as a Meyer Sound SIM3 system, to evaluate audio response. The SIM3 shows a ruler-flat frequency and phase response and a latency of just 0.29. We neither saw nor heard any degradation in quality when both video and audio were connected compared to the two connected separately.

However, there are a couple of caveats. First, we’d prefer the option of XLR audio connectors to the 1/8in. mini connector on the 7220, although the physical size of the current design wouldn’t allow it. Second, the 7220 supports video resolutions from VGA up to WXGA (1366×768), as well as HDTV signals in 480p, 720p, and 1080i. That makes it an excellent solution for distributing motion video or television content; for example, sending CNN’s Airport channel from a single control room out to the TVs in the gate area. However, the 7220 does not support higher computer resolutions.

We were able to transmit a slightly higher-resolution 1152×864, 60Hz signal, but the images were noticeably soft. A 1280×1024 computer source was not received. Communications Specialties notes that fiber is still an evolving technology and that, while WXGA with audio over a single-mode cable is a something of a fiber industry breakthrough today, higher-resolution support over the same single-mode cable is on the horizon, and there won’t be the need to upgrade any cable infrastructure.


Compare that to copper cable. There is no such resolution limitation with some of the existing solutions that faciliate long-distance video over Cat-5 up to 1,000ft. and higher. That’s about 180ft. more than the 250m (820ft.) of cable included with the 7220-KIT. And while bulk single-mode fiber optic cable can cost as little as 10¢ per foot, that’s still more than double the cost of bulk Cat-5.

Why turn to fiber optic? The obvious reason would be if that 250m were not enough, and if your overall installation needs were much greater, as might be the case between terminals in an airport, across the campus of a college or university, or even between adjacent office buildings or warehouses. Communications Specialties cites tests that show the 7220 sending a clean signal up to 37km, or 23 miles. You’re just not going to do that with Cat-5. Admittedly, for shorter distances (if you consider 250m “short” or go much shorter than that), the 7220-KIT solutions is probably going to be more expensive than more traditional cable. That $1,000 for each the transmitter and receiver is more than you’d have to pay for any number of Cat-5 repeaters or video interface solutions to cover distances in the hundreds of feet (not meters). Although the 7220-KIT is comparable to the transmitter and receiver required for Magenta Research’s MultiView AK 1,500ft. solution.

Still, there are compelling reasons to look at fiber, especially in today’s security-conscious world. The government, for example, is increasingly turning to fiber even for shorter cable distances because it is almost impossible to tap into a fiber optic cable to steal information without disrupting the signal. Break the path of light, and there’s no data to steal. The same is true for closed-circuit security cameras. Fiber is also far less susceptible to RF interference than copper cable. You can run fiber cable beside other cabling, even power lines, without concern for signal integrity.

Communications Specialties would want to add that despite fiber’s reputation, installing fiber optic cable and running signals is ultimately easier than traditional Cat-5 solutions, citing copper’s need for multiple repeaters over longer distances and the tweaking necessary to adjust and perfect signals. Admittedly, “easier” is in the eye of the beholder, and familiarity with those traditional solutions goes a long way toward “ease.”

On the other hand, the Pure Digital FiberLink 7220-KIT does prove that fiber is not at all complicated, that the included cabling is not at all fragile, and that making the physical connections is a piece of cake. Communications Specialties even sells an easy do-it-yourself fiber optic termination kit. The termination kit costs a hefty $1,500, but that’s likely to be a small portion of the cost of any video installation that’s measured in hundreds of meters rather than hundreds of inches or feet.

More important, the Communication Specialties Pure Digital FiberLink 7220-KIT — along with the mere existence of that termination kit — proves that there’s nothing particularly forbidding about working with fiber optics for AV installations.


Company: Communications Specialties;

Pros: Very easy to set up; no repeating or calibration necessary.

Cons: Higher computer resolutions not supported.

Applications: AV transmission across far-flung campuses; high-security transmission.

Price: $2,695



Number of Audio Channels 2, unbalanced

Frequency Response +0/-0.5 dB, 20Hz-20kHz

Bits-per-Sample/Sampling Rate 24 bits; 54kHz

Maximum Audio Level +10dBu

SNR (A-Weighted) 95dB

Input Impedance >24 kΩ

Output Impedance < 1Ω

Audio to Video Diff. Delay (skew) <300 uSec


Number of Video Channels 1 RGBHV

RGB Processing 24 bits, no compression, scaling, or Color-space conversion

Input Impedance RGB: 75Ω; H & V: Hi-Z

Input Level RGB: 714 mV p-p; H & V: 3 to 5 V p-p

H Synch Frequency Range 15 to 60kHz

V Synch Frequency Range 30 to 85Hz

RGB Format Supported RGB with separate H and V


Power Requirements 9-24V AC or DC, 5W

Operating Wavelength 1310nm

Dimensions (W×H×D) 5″×1.15″×5.25″

Weight Approx. 10 oz.

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