Satellite TV gets small

Satellite communications antennas seem to operate on an inverse corollary of Moore’s Law. The law, first observed by Intel executive Gordon Moore, states that the number of transistors on a computer chip will double about every two years. The corollary seems to be that satellite TV antennas will get progressively smaller. Perhaps one day we will watch satellite TV on a Blackberry-size device.

The latest marine satellite TV antenna products from KVH Industries and Intellian Technologies are following this trend. Both companies have produced units small enough for mounting on smaller vessels. These units will fit on boats in the 20 to 30-foot range. And what is even more surprising is that these are actively-stabilized units and will gather in a satellite signal while a vessel is moving. It seems that just a few years ago, KVH Industries antenna experts were telling us that satellite TV antennas couldn’t get any smaller than they already were. “It was a matter of physics,” they explained. The laws of the universe couldn’t be circumvented. It seems, however, that KVH and Intellian engineers have discovered a way to tweak them a little.

KVH’s new unit is the TracVision M1, while the Intellian product is called the i1. Both are impressively small: the TracVision M1 is a mere 7.5 pounds and the antenna measures a scant 12.5 inches, while the Intellian i1 is a bit heavier at 9.4 pounds and with an antenna dimension of 11 inches. What these physical specs mean, of course, is that even relatively small boats can be equipped to receive satellite TV.

How do these small antennas accomplish the task of picking up a faint satellite signal from 23,000 miles out in space? The solution involves an intriguing combination of hardware and software techniques.

KVH’s M1 uses a classic satellite antenna dish, but has devised a few techniques for squeezing out the maximum useable signal. KVH’s package of signal enhancers goes by the name of RingFire technology. A dish antenna collects the signal and bounces it to a splash plate mounted at the top of the central feed tube. The splash plate then reflects the signal through a “feed window” at the top of the feed tube. This double bounce of the signal from a dish to a central reflector puts the M1 into the category of a Cassegrain-type antenna. Cassegrain antennas aren’t only for radio frequencies, the double reflection principle works with visible light too. Many reflector-type amateur astronomy telescopes are also Cassegrain units, using large and small coaxial mirrors to concentrate visible light from distant planets to the telescope’s eyepiece.

On KVH’s M1, the feed tube is a hollow circular waveguide. The concentrated satellite signal propagates down the tube to a device called a low noise block (LNB), which is located up against the back of the dish. The LNB is a highly engineered electronic unit that gathers the satellite signal and then converts it from the satellite broadcast frequency (12 GHz Ku band) to an intermediate frequency (1.5 Ghz L band) that is easier for the satellite receiver to manipulate. To concentrate LNB weight and to allow the unit handle multiple frequencies, KVH’s LNB is a set of stacked components. From the LNB the signal travels via wire to the satellite receiver in the boat. According to Chris Watson, director of marketing for KVH, the design of the antenna and LNB has been optimized for top performance. “This unit is designed to tune out noise and lose as little [signal] energy as possible.”

Two advantages of using the Cassegrain double-reflection approach are that the splash plate can be small and thus not block the signal collecting area of the dish and the LNB is right next to the dish, not at the end of an arm above the dish. This makes for a more compact mass that is easier for the antenna’s motors to slew around when a boat is underway and the antenna is working to stay locked onto a satellite signal.

The Intellian i1 also uses the Cassegrain approach, placing the LNB at the bottom of the feed tube, behind the dish. The i1 makes use of a few software techniques for improving its receiving ability. For finding the satellite signal, the i1 utilizes a patented algorithm called Wide Range Search for minimizing search time. For staying locked onto the signal once the satellite has been acquired, the i1 employs a technique Intellian calls Dynamic Beam Tilting (DBT) to keep the signal strong and to reduce the need for moving the antenna. The DBT technique means that a sub reflector of the antenna, the smaller reflector at the top of the feed tube, spins on a slightly tilted axis. A combination of the spin, the tilt and the special shape of the sub reflector allows the i1 to look off to the side. This allows the i1 to electronically sample incoming signal strength to ensure it is getting the best signal, without having to physically move the whole antenna. “The antenna doesn’t have to do all that hunting around,” said John Minetola, director of U.S. sales for Intellian. “It doesn’t have to move the big dish.”

The KVH M1 and the Intellian i1 are intended for use with the direct broadcast TV satellites that sit in a geosynchronous orbit over North America. And, of course, there is a price to pay for the smaller, lighter dish. While the larger satellite TV antennas offered by both KVH and Intellian can be used as much as 100 to 200 miles offshore, the smaller size of the M1 and the i1 means these antennas can’t gather enough useable signal as the units reach the edge of a satellite’s beam. Thus, these smaller satellite antenna products can only be used 20 to 75 miles offshore.

An important point, however, is that the technology developed for these smaller antennas is also used on the larger antennas offered by KVH and Intellian, improving the performance of all satellite TV products.

According to KVH, the M1 antenna unit has a list price of $2,995, which includes the antenna unit, 50 feet of RG6 cable and a satellite TV receiver/controller. The Intellian i1 has a suggested price of $2,795, including cabling and an antenna control unit.

By Ocean Navigator