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Your RF Cafe
Airplanes and Rockets:
Issue: February 2012
FCC Narrowbanding Deadline
There’s now less than a year left before the FCC’s narrowbanding edict goes into effect when all public safety and business land mobile radio systems operating in the 150 to 174 and 421 to 512 MHz bands must switch from 25 kHz to 12.5 kHz channels. The FCC’s mandate covers public safety systems, public utilities, schools, transportation departments, and mass transit. Services that don’t comply by January 1, 2013 will be subject to FCC enforcement action that can include fines or loss of license. It translates into one voice path in a 12.5 kHz channel, two voice paths in a 25 kHz channel, or data channels with data rates greater than 4.8 Kb/s per 6.25 kHz channel. Modulation can be either analog or digital as long as they have “12.5-kHz efficiency”.
Designers of receiver multicouplers and transmit/receive distribution networks (among other subsystems) need more stringent receive filtering--and crystal filters are the obvious choice for achieving it. Anatech has been designing standard and custom filters for just this application for more than 20 years. They’re used in receivers that operate in every channel of type of affected system and exhibit the exceptional performance that narrowbanding will require.
Based on our vast library of designs, we can manufacture crystal filters for any frequency band covered by the mandate that meet the requirements for highly-selective filtering. For more information, please call us at (973) 772-4242 or send us an e-mail to
Microwaves to Speed Drug Development?
English company Uniqsis and Sweden's WaveCraft are jointly developing microwave-based flow chemistry systems to improve the ability to scale up compound synthesis during drug development. The team will integrate Uniqsis’ microwave applicator technology and WaveCraft reactors. WaveCraft’s technology uses an applicator and proprietary microwave generator based on mobile phone technology to apply microwave energy and accelerate chemical reactions. Combining flow chemistry with microwave heating could enable researchers to continuously change power and frequency to optimize synthesis reactions. Scale-up could then be carried out without the need to re-optimize conditions.
Help Us Out… Get a Spectrum Chart!
We’re interested in your opinion and we know how valuable your time is. So if you would please take a few minutes to answer our short questionnaire, we’ll send you a copy of the complete U.S. frequency spectrum chart in full color spectrum chart…always a handy reference.
Please click here to take the survey….and thanks in advance!
The Filter Answer Man
The first of our new series of tutorials on filter and other product characteristics is provided this month
by Chung Au, our international sales manager, who answers some questions he recently received.
Duplexers and Diplexers
These two terms are often used interchangeably when in fact they are two different types of devices. A diplexer is a three-port network that separates incoming signals from one port into two paths. The input signals must be different enough in frequency to allow filters to provide unhindered rejection. Conversely, a duplexer is also a three port network but it instead allows a transmitter and receiver to use the same antenna at the same frequency. In both cases a high degree of rejection is required to ensure that the signals do not interfere with each other.
When specifying a notch filter, we have been asked to provide a design with the same passband frequencies and notch frequencies. The conflict is obvious when shown graphically:
We have often been asked to provide SAW filters with very wide bandwidths, in the latest case 91 MHz with a center frequency of 870 MHz. However, such a bandwidth is too wide for a SAW filter with this bandwidth as the maximum can 10% or less of the center frequency.
Testing for the “Real World”
A seemingly obvious yet often overlooked requirement for system designers is subjecting the finished product to signals and a signal environment in which it will actually operate. This was once just “desirable” but thanks to close channel spacing and an overcrowded spectrum, designers who fail to evaluate their products under worst-case can conditions do so at their peril.
Fortunately, modern test equipment makes it possible to create simulated signal environments with relative ease. In addition, there are system-level software tools that allow a circuit design to be evaluated and modified by subjecting them to real-world signals. Such efforts may take more time, but are well worth the effort.
The Importance of Rejection
The rejection of out-of-band signals is obviously the primary goal of every filter but the specification has taken on new meaning in today's congested spectrum. As a result, in order to effectively attenuate a signal 3 MHz from the desired signal the filter must have rejection of at least 40 dB outside its passband. Less rejection can be tolerated in some circumstances but these are fewer and fewer every day. Duplexers must have especially sharp cutoff characteristics as well as high isolation and the lowest possible insertion loss so that that neither the receive or transmit frequencies will interfere with each other.
A Message from
Every day we get requests from current and prospective customers for filters and other products with specifications that simply cannot be achieved -- by anyone. We also get questions such as the first one in this issue about diplexers and duplexers, which are often considered the same thing but aren't.
With that in mind, beginning this month we are dedicating the center column of the Anatech Electronics newsletter to answering common questions posed by our customers. Some may seem simple and others will be notoriously complex, but we’re hoping novices and veterans alike will benefit from a little “refresher”. We hope you find this information useful.
New Functionality for AMCrf.com!
We have just added several new features to our Web store, www.AMCrf.com, that make it more informative and easier to use. We have categorized products by specific applications, added more relevant content to the banner area at the top of the home page, and several other features we hope will make specifying our products easier than ever before.
Taiwan Stays with WiMAX
As the world moves to LTE, WiMAX subscribers are growing fast in Taiwan. The government says it will push development of WiMAX applications to help the countries six WiMAX operators expand their networks.
Did you know...
1. The Internet was originally called ARPANet (Advanced Research Projects Agency Network) designed by the US Department of Defense.
2. In 1878 the first telephone book ever made contained only 50 names.
3. Originally in 1886 Coca Cola was introduced as an 'intellectual beverage' to boost brain power.
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