Most Popular Articles
Satellites and Radio: Always something new and exciting
So much is happening in the way of satellite communications that it's hard to keep track of it all.
In the beginning, there was analog. It was just plain audio with different services using various bandwidths, pre-emphasis, and sometimes companding, the combination of compression and expansion to improve signal to noise figures. Its main problem was that it needed a definite signal-to-noise ratio to work properly, requiring a relatively high carrier power level, especially with companding. Audio quality was variable, to say the least. Plus, it offered no security features. Those who generated the programming had no control over who could receive it. Pirating, while not rampant, was a problem. Then Scientific Atlanta developed the Digital Audio Transmission (DAT) format. It overcame the problems of noisy audio by digitally encoding the audio for transmission. This eliminated the variable audio quality factor, but introduced the true nature of digital: it either worked or it didn't. The pirating problem was temporarily solved because only a few manufacturers made DAT receivers. At that time, Scientific Atlanta and Fairchild were the only choices available.
The problem with DAT was bandwidth. A maximum of 16 15kHz audio channels would occupy an entire transponder. These could be divided into as many as 32 7.5kHz channels.
The next step was Spectrum Efficient Digital Audio Transmission (SEDAT). Using digital compression, SEDAT was able to triple the number of high-quality audio channels on one satellite transponder. It also offered an increased frequency response of 20kHz.
Along the way, Starguide Digital was born. Starguide eventually obtained the rights to DAT and SEDAT from Scientific-Atlanta and began marketing the Starguide receiver. It could receive both DAT and SEDAT-encoded signals and served as a bridge to the new generation of satellite audio technology.
Through Starguide's affiliation with Musicam, the Musicam encoding format was pressed into satellite service. Musicam is a modified version of the MPEG Layer II digital encoding standard. The Starguide II receivers were the first to use this new technology for broadcasters. The Starguide II receiver also solved the unauthorized use of satellite programming by requiring all reception to be permissioned. Starguide III receivers will use an upgraded version of Musicam when the transition is made to a new satellite next year.
Up in the sky Over the last decade, satellite Satcom C-5 (and its predecessors in the same orbital slot) has been the backbone for many broadcasters' network audio needs. But C-5's time is running out; while there are no technical problems now, the satellite will soon run out of the gas used to keep it in a stationary orbit. Many rumors regarding the future of that orbital slot have floated about, and many broadcasters have been nervous about where they will continue to get their vital programming. But do not worry. It is already planned, for the second quarter of next year, that Satcom C-5 will be replaced with a new bird, designated GE-8. The switch to the new satellite will be seamless, with no loss of satellite service anticipated. In fact, users won't even know it has occurred. GE-8 will have a signal 3dB to 4dB stronger than Satcom C-5.
One change will be apparent after switching to the new satellite. Your Starguide II receivers will no longer work. So if you haven't already done so, plan now to replace your Starguide II receiver with a Starguide III.
Many Starguide II owners have asked if these units can be upgraded to a Starguide III. The short answer is no. Although the front panel of the Starguide III looks almost identical to the II, the internal circuitry is completely different. The critical circuits are not on plug-in cards that can simply be replaced. One major difference is that the Starguide III receiver must have an input bandwidth of 25Mb, where the older Starguide receivers had an input bandwidth of 6Mb.
The smallest recommended satellite dish diameter is now 3.7 or 3.8 meters. The issue is not gain, but rather directionality. As a rule, the larger the dish, the smaller the angle or beamwidth that the dish can see in the sky. This wasn't critical a decade ago when satellites were spaced 4 degrees apart. But now they are spaced at 2 degrees. An older dish made in the 1980s might be seeing at least two and maybe three satellites all at the same time. And while you're at it, don't invest in a mesh dish. These dishes are flimsy, compared to solid dishes. They are too easily bent or warped. And the uneven surface adds phase noise to your received signal. Phase noise is a major problem when trying to receive the new quadrature phase shift keying (QPSK) signals. A 12-foot mesh dish, even if not warped out of shape, will not perform as well as a solid dish of the same size. Also, once any ice forms or debris settles on a mesh dish, any wind loading advantage is lost.
Why is this critical now? For one thing, plans are already in progress to replace satellite Satcom C1 - and in orbital slot 137 degrees West, it's right next door to Satcom C-5 at 139 degrees West. C-1 will also have a higher output power level, and hence, a greater possibility to interfere with Satcom C-5 and/or GE-8.
Available services NSN is promoting the use of their Supercarrier audio distribution system. This service uses a multi-channel carrier on the Satcom C-5 satellite. The service is geared mainly towards major network users, such as Rush Limbaugh, Dr. Laura, Dr. Dean Edel, etc. The Supercarrier is most suited to networks that have at least 200 customers who downlink from them. Supercarrier is received on a Starguide II or III satellite receiver.
NSN also offers data and IP links on their Supercarrier services, with data rates as high as 10Mb/s. They report they have had little call for this so far, but they believe there will eventually be a demand.
Traditional uplinking and downlinking for smaller businesses and radio/audio networks is still a big business. PAS (PanAmSat) offers Ku-band service on its fleet of Galaxy satellites. Unlike large networks such as Supercarrier, Ku system users have total control over their signals, from the uplink (usually at the customers' premises) to the downlink. Service is usually partitioned by chunks of bandwidth rather than audio channels, as in the past. 64kb/s service is usually satisfactory for a mono audio signal and 128kb/s for stereo. Segments up to 384kb/s are available. Users of these type links commonly use the Layer II coding scheme for data reduction.
NPR Satellite Services now offers both C-band and Ku-band satellite links and sells the necessary equipment as well. They lease bandwidth segments from as little as 64kb/s up to T1, using satellite Galaxy IV-R.
What's the difference between Ku-band and C-band? Aside from the obvious difference in frequency, C-band is almost immune to weather-related service interruptions, also known as rain fade. But overall, C-band is the more expensive of the two systems to build and operate.
A report on satellite networks would not be complete without mentioning the Christian Radio Coalition (CRC). Using Spacecom's GE-3 satellite, the CRC combined the individual networks of its members into one digital video broadcasting (DVB) MPEG-2 carrier. This allowed all of the CRC member network affiliates to standardize on one receiver, the Wegener Unity 4000, which can be used to pick up programming from all CRC member networks. The transition occurred earlier this year. I can personally attest that it was a colossal undertaking, as I was actively involved in installing dishes and receivers here at LifeTalk Radio. The CRC has effectively met the needs of religious broadcasters who want to transmit programs from many different Christian networks.
And finally, if you want to explore the heavens for satellites and phenomenon of many types, check out www.heavens-above.com. There you will find information on tracking (from the ground) satellites, space stations, and even something called Iridium flares. You'll have to go to the website and find out for yourself what this is all about.
Everyone is used to receiving audio programming via satellite now, but many satellite service providers are now offering IP services as well. NSN Networks, for example, offers INSAT data service. The basic system consists of a satellite dish and receiver, which connects to your computer. You can download data from the Internet at speeds exceeding a T1 circuit. In fact, according to NSN, T1 speed is the minimum you can expect. It's 10 times faster than ADSL and 100 times faster than ISDN.
At least two companies are offering IP uplink service as well. NSN has a companion uplink system to go with their high-speed downlink service. The uplink speed isn't necessarily as fast as the downlink - the speed ranges from 32kb/s to a maximum of 2Mb/s, depending on the package you buy. These services are intended for businesses and ISPs and are not aimed at the home IP-user market. INSAT data services use the GE-4 satellite.
Radio Shack offers satellite-to-home IP service, but its use is contingent on purchasing a computer from Radio Shack. A helpful and talkative salesman at a nearby store told me that for about $1,248 you get a computer with a proprietary card, a 2' by 3' oval satellite dish and the associated electronics. But the service is (relatively speaking) stupendous. The upload speed is between 500kb/s and 700kb/s, and the download speed will burst as high as 5Mb/s - about the rate of a T3. The monthly service fee is $59.95 for unlimited usage. Internet service is provided by the Microsoft Network.
As I said, this offer requires you to purchase a computer, but this requirement may change sometime next year, and the service will be offered as an aftermarket system. The satellite dish and electronics are leased, by the way, and remain the property of the satellite service provider.
Acceptable Use Policy blog comments powered by Disqus
[an error occurred while processing this directive]
Today in Radio History
The history of radio broadcasting extends beyond the work of a few famous inventors.
Read each issue online in our Digital Edition Format in your Web browser.
EAS Information More on EAS
The feed provides feeds for all US states and territories.
Need a calendar for your computer desktop? Use one of ours.
Information from manufacturers and associations about industry news, products, technology and business announcements.
When building its new broadcast production vehicle, MRN applied lessons learned from the past.
Browse Back Issues[an error occurred while processing this directive]
Also in the April Issue
- Update on Transmitters
- On-air Missteps to Avoid
- Tower Lease Renegotiation
- New Products
- Applied Technology: Streaming with the MPEG HE-AAC Audio Codec
- Side by Side: Studio Furniture
- Practical Use: Circulators and Isolators