Wednesday, December 17, 2008

Dielectric Resonator Oscillators (DRO)

Dielectric Resonator Oscillators (DRO) are used widely in today's electronic warfare, missile, radar and communication systems. They find use both in military and commercial applications. The DROs are characterized by low phase noise, compact size, frequency stability with temperature, ease of integration with other hybrid MIC circuitries, simple construction and the ability to withstand harsh environments.

These characteristics make DROs a natural choice both for fundamental oscillators and as the sources for oscillators that are phase-locked to reference frequencies, such as crystal oscillators.

This paper summarizes design techniques for DROs and the voltage- tuning DRO (VT-DRO), and presents measured data for them including phase noise, frequency stability and pulsing characteristics.

Design Techniques

The design technique we will discuss is for a dielectric resonator (DR) to be used as a series feedback element. Practically, a GaAs FET or a Si-bipolar transistor is chosen as the active device for the oscillator portion of the DRO circuit. The Si-bipolar transistor is generally selected for lower phase noise characteristics, while the GaAs FET is required for higher frequencies.

For example, a DRO with a DR as a series feedback element can be designed using following design procedure:

1. Select an active device that is capable of oscillation at the design frequency, and use the small signal S-parameter of the device for the design.
2. Add a feedback circuit to ensure that the stability factor of the active device with the feedback circuit is less than unity with enough margin.
3. Create an active one-port analysis that consists of the active device, the feedback circuit, the matching network and the load as shown as figure1. Optimize Za (?) with the parameters in the feedback circuit and in the matching network to ensure that Ra (?0) is less than or equal to -25 ohms and Xa (?) has the possible maximum variation near resonance in order to insure high circuit Q.

Friday, December 5, 2008

Wireless Optical Mesh Solution Networks

ClearMesh Networks Wednesday launched a wireless optical mesh solution designed to fill the gap between copper, RF and fiber in delivering 5mbps to 100mbps services to small and midsized businesses.

“There isn’t a cost-effective way for carriers today to extend fiber to SMBs,” said Fima Vaisman, ClearMesh’s senior vice president of marketing, explaining their monthly spend of $500 to $1,000 does not support a fiber trench where it is not already available. “What we provide is a solution that extends the fiber core without having to trench fiber.”

It also provides higher bandwidth than do copper and RF solutions, such as Wi-Fi and WiMAX, he said. “If a customer needs more bandwidth and they are looking for an SLA, we think there is a gap between those solutions provided at the entry level by WiMAX and Wi-Fi, and the high-end level by fiber. There is a gap in the middle. That is the gap we are trying to serve.”

Available immediately, the ClearMesh Metro Grid solution includes the ClearMesh 300 node, which can be mounted on a pole or rooftop, and the ClearMesh Management System, which provides tools for installation, diagnostics, service analysis and provisioning. The ClearMesh 300 node combines wireless and optical technologies with a Layer 2 mesh architecture to deliver business-grade Ethernet.

“The ClearMesh 300 Node is a switching platform,” explained Vaisman. “It has an Ethernet switch with 2-gigabit Ethernet capacity. Four of the Ethernet ports are copper and they are connected to optical transceivers.”

The optical transceivers, he said, are LED-based, which gives them a wider beam than systems using lasers, like free-space optics. “What that allows the product to do is be installed on a light pole as well as on top of a building,” said Vaisman. “A laser product cannot be installed on a light pole because the light pole has too much vibration, too much movement. The product wouldn’t stay locked on. With the product we have the light beams are locked on and stay locked on using automatic tracking whether on a light pole or building. With that you have a much broader ability to deploy a mesh in a metro area. If the device moves, the light cone still hits the other node.”

Each node has three optical transceivers, which operate on the license-free 850nm light band and reach 250 meters. Each transceiver is motorized, so it can move independently up and down, and 360 degrees around. “This allows each node to see three other nodes. Using that, we create a mesh,” said Vaisman, explaining the mesh requires one node to be fiber-feed, and several nodes can be fed from the same fiber to increase the capacity delivered into the mesh.

The ClearMesh node lists for $6,000, and less in volume. Considering installation costs, the company uses $5,000 per node in its ROI calculations. In contrast to trenching fiber, ClearMesh can cover seven buldings in a MetroGrid network for $35,000 in a matter of days while the fiber deployment over the same area will cost $180,000 and take months to install, he said. With a single customer per building and a single T1 replacement at $500 per month, the payback is 10 months, Vaisman said, adding a more realistic scenario is three customers per building paying $750 per month for a 10mbps service for an ROI of two months.

Yankee Group Analyst Tara Howard agrees that the ClearMesh solution serves “as a logical extension of a fiber network,” but she questions the market potential, discounting its appeal to Tier 1 companies that are laying fiber. “The opportunity is going to be with local LECs and municipalities,” she said, adding the fact that it does not compete with Wi-Fi or WiMAX is a plus.

“We don’t do what Wi-Fi does; we don’t offer mobility,” said Vaisman. “We don’t do what WiMAX does; we don’t offer five-mile reach. In a dense metro area, we offer high bandwidth and the ability to sign SLAs without any interference,” he said. The systems offers latency at one-tenth of 1ms, so 10 nodes equals 1ms of delay.

Wirelss Wide Area Network

Wirelss Wide Area Network A WWAN differs from a WLAN (wireless LAN) in that it uses Mobile telecommunication cellular network technologies such as WIMAX (though it's better applicated into WMAN Networks), UMTS, GPRS, CDMA2000, GSM, CDPD, Mobitex, HSDPA or 3G to transfer data. It can use also LMDS and Wi-Fi to connect to the Internet. These cellular technologies are offered regionally, nationwide, or even globally and are provided by a wireless service provider for a monthly usage fee.[1] WWAN connectivity allows a user with a laptop and a WWAN card to surf the web, check email, or connect to a Virtual Private Network (VPN) from anywhere within the regional boundaries of cellular service. Various computers now have integrated WWAN capabilities (Such as HSDPA in Centrino). This means that the system has a cellular radio (GSM/CDMA) built in, which allows the user to send and receive data. There are two basic means that a mobile network may use to transfer data:
Packet-switched Data Networks (GPRS/CDPD)
Circuit-switched dial-up connections
Since radio communications systems do not provide a physically secure connection path, WWANs typically incorporate encryption and authentication methods to make them more secure. Unfortunately some of the early GSM encryption techniques were flawed, and security experts have issued warnings that cellular communication, including WWANs, is no longer secure.[2] UMTS(3G) encryption was developed later and has yet to be broken.
Examples of providers for WWAN include Sprint Nextel, Verizon, and AT&T.

Thursday, December 4, 2008

Oxygen Sensor Analyzer

An oxygen sensor, or lambda sensor, is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analyzed. It was developed by Robert Bosch GmbH during the late 1960s under supervision by Dr. G√ľnter Bauman. The original sensing element is made with a thimble-shaped zirconia ceramic coated on both the exhaust and reference sides with a thin layer of platinum and comes in both heated and unheated forms. The planar-style sensor entered the market in 1998 (also pioneered by Robert Bosch GmbH) and significantly reduced the mass of the ceramic sensing element as well as incorporating the heater within the ceramic structure. This resulted in a sensor that both started operating sooner and responded faster. The most common application is to measure the exhaust gas concentration of oxygen for internal combustion engines in automobiles and other vehicles. Divers also use a similar device to measure the partial pressure of oxygen in their breathing gas.

Scientists use oxygen sensors to measure respiration or production of oxygen and use a different approach. Oxygen sensors are used in oxygen analyzers which find a lot of use in medical applications such as anesthesia monitors, respirators and oxygen concentrators.

There are many different ways of measuring oxygen and these include technologies such as zirconia, electrochemical (also known as Galvanic), infrared, ultrasonic and very recently laser. Each method has its own advantages and disadvantages.

Saturday, November 22, 2008

Analog Television

Digital Satellite TV - End of Analog Television

That is not to say that there are not any other online retailers of digital satellite TV services; it is just that there is very little choice in type of services being offered and most of these providers only differ from one another in their marketing and promotional offers, and nothing else. This is certainly a big constraint given the fact that watching digital satellite TV will only be enjoyable if there are more than a few options to choose from.

Digital satellite TV represents a quantum leap in quality over the traditional analog TVs that for long were the only types of television sets available on the market. However, even if you have bought a satellite TV you will still need to ensure that the set that you purchased must be able to handle the kind of resolution required to get the most out of your service.

In addition, you will also require buying a satellite television system that consists of a receiver as well as satellite dish and which is essential to enjoying your channels. Besides improvement in quality of pictures that a digital TV provides you, you are also sure to get more choice in regard to larger selection of television channels as compared to what is available with analog television sets.

However, not everything about watching satellite TV is hunky-dory as there is a minor downside to contend with, especially in that bad weather conditions which will cause severe disturbance to your viewing because strong winds or even storms can sever your television connection and then all that you will see on your television screen would be fuzzy pictures or no pictures at all.

Other than this minor hiccup, a digital satellite TV outpoints the analog television set on all counts and that is why people have given up buying analog television sets. Furthermore, if you are keen on watching premium or even pay-per-view television broadcasts you will also need to buy a digital TV descrambler.

The current popularity of the digital satellite TV makes it almost impossible not to also buy one for your television viewing; and, if you have teenagers in your home you would have no option but to accede to their demands for a digital satellite TV without which they would not be able to their favorite television channels.

Broadband TV

In the last issue of Ariadne I explored available streaming video on the web (Tiny TV, Ariadne issue 22, December 1999), looking at the phenomenon particularly according to the geographic and subject distribution of resources.

Things are moving very fast: by the time the article was published the version of RealPlayer (G2) had been replaced, and my written map of available resources was much narrower than the range of materials which I knew to exist. Many more films and TV shows are available, mostly at cable modem speeds of transmission, and a number of servers appear to have stopped broadcasting, at least from the addresses which were valid and active in December 1999.

Most of what I explored was lowband: video streams arriving at rates between 8 kilobits per second, up to 60 kilobits per second. These are services which (by and large, with occasional pauses to replenish the buffer) can be received and played adequately via a 56k modem on a computer with a greater than 100khz chip. Some items listed in the article however, particularly the film resources, come in at up to 250 kilobits per second. I included these because they were available resources, though not every reader of the article would be able to play the streams.

The Tiny TV article was written in November, and before it was completed I became aware of a number of servers which were distributing broadband streaming video, at speeds in excess of 300 kilobits per second, and sometimes well over 400 kilobits per second. These were not included in the article, partly because of pressure of time, and partly due to a delay caused by some of the streams arriving on port 554, which is one which, here at least, was closed by default. If you have a machine and a network connection capable of handling these higher rate bitstreams (ISDN, cable modem access, T3 connection, etc), but get an error message saying that the port is closed, you will have to ask your system administrator to open the port.

The quality of these transmissions is very high. The default window size is around twice what was enjoyed in the Tiny TV experience, and the window size can often be doubled again without the image becoming unpleasant to watch. Full screen display is just a bit too much, and your computer is not likely to handle the screen redraws necessary, unless it is top of the line. I used a two year old 233 mhz Pentium II, which worked fine with the fastest streams, with the screen window set at 200 per cent.

For the purposes of this article, broadband is defined as anything streaming at a rate in excess of 56kbs. The fastest available I have seen so far is 700kbs. Everything above 56kbs is broadband, since ordinary modem users will not be able to see the streams as intended. So 56kbs is a reasonable definition of where broadband starts. Some items are available at various speeds from 20kbs up to 250kbs, so users interested in broadband should not neglect the lowband listing, since what you are looking for might be there. No items listed arrive faster than 420kbs. I've listed only items which seem reliable and which come up fairly fast. Anything which is intermittent or slow I've omitted from the lists.

Most of what is available at these higher speeds is either commercial film and television (of a certain vintage), or music video (usually modern). There is also some academic material of very high quality. It doesn't make much sense to make news programming available in broadband (not at the moment at any rate), so there isn't much of that around. But there is some. Most of the material comes from a handful of servers, mostly based in the United States. The categories used are as follows: Broadband : Europe; North America; South America; Asia; Middle East; Africa; Drama; Archive Television; Other Educational Resources; Financial Services; Religious Broadcasting; Sport; Commercial Film; Art Film; Music. Lowband follows the same arrangement, with the addition of a 'miscellaneous' section. The coverage in this article is uneven, since I don't have unlimited amounts of time to survey available content and to check the reliability of links. I haven't included as many commercial films as I did in the last article, but by following up the addresses of the main listings you should be able to find these easily enough. Where I haven't found anything worth mentioning in a particular category, I've linked back to the Tiny TV article in issue 22, and/or to the Broadband/Lowband section of this article, as appropriate.

Broadband TV Origin

Broadband TV involves accessing multimedia content via an unmanaged broadband connection and viewing it on a PC or sometimes a normal TV. Broadband TV differs from IPTV as the network bandwidth is unmanaged and the system is inherently open. Broadband TV is the same as Internet TV which is usually referred to as accessing TV video streams over general purpose broadband internet. IPTV differs from Broadband and Internet TV, as it is a closed system for the delivery of PayTV services with an assured Quality of Service underpinned by an operator's investment in network infrastructure, content rights and consumer equipment.

The current commercial focus is around developing video on demand services to the home. Multimedia content can be personalised for individual users and can be called personalised TV.

In 1999 most people did not watch video online. A company called Teveo used a high speed Internet connection to connect thousands of dial up users using player less video technology. The evolution of Broadband connections made it possible for Internet users to become real time video broadcasters using Teveo. Teveo produced technology that was ahead of its time and did not survive the Internet bubble burst of 2000, as a result Teveo software can still be downloaded free on the Internet. You got Broadband? became common question around year the 2000, many Broadband TV pioneers began streaming music videos online using a Broadband Internet connection. In 2003 a little known Internet Pioneer named Enas E. Ragland launched one of America's first Broadband Broadcasting Networks and called the technology Broadband TV (BE TV) in part because of the platforms ability to emulate old style Television via Broadband Internet connection.

Currently Broadband pioneers use the explict generic mark "Broadband TV" to define evolving video Technologies. Unlike Internet TV or IPTV, advanced Broadband TV technologies like "Broadband Messaging" allow users to engage in real time using cams, pictures, voice, video, text and more. When the Broadband Broadcasting market mature in a few years, Internet TV will be defined as it is exist now, Broadband TV is expected to be defined as an interactive Broadband Broadcasting format. Advanced Broadband Broadcasting formats allow users to access Broadband TV, Radio with images, Voice, Video, cams, text, record, pictures and media downloading in a user controlled Broadband Messaging environment. Broadband TV is without question competing with traditional Television and Internet TV. Broadband media programming is one of the fasting growing sources of revenue online. The word Broadband allow search engines to identify the underlying product as Broadband Media. "Broadband" identification help provide more accurate search results when compared to the search phrase Internet TV. On behalf on the Internet pioneers who are developing the generic term Broadband TV, it is our opinion that Broadband TV should not be merged with Internet TV.