1996 - 2016
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...
All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.
My Hobby Website:
These archive pages are provided in order to make it easier for you to find items that you remember seeing on the RF Cafe homepage. Of course probably the easiest way to find anything on the website is to use the "Search RF Cafe" box at the top of every page.
Homepage Archive Pages
2016: Jan |
Feb | Mar |
Apr | May |
Jun | Jul |
Aug | Sep |
Oct | Nov |
2015: Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec
2014: Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec
2013: Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec
2012: Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec
2011: Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec
2010: Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec
2009: Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec
How We Listen to
Stars and Satellites
If you have never paid much attention to the state of the art in telescopes, then you might believe they consist of either the $99 Tasco jobs in Walmart's toy department or the 200" Hale atop Mount Palomar. You might also think that objects which emit or reflect light in the visible spectrum are the only things studied. You might not know that radio telescopes have been built to detect frequencies ranging from HF all the way up into cosmic rays. Newer telescopes search for gravity waves and even neutrino and 'dark matter' pseudo particles. You might not know that there is a broad selection of optical telescopes for amateur and research grade telescopes and that the line between amateur and research grade telescopes...
Copper Mountain Adds 4 Port
Planar 808/1 to VNA Line
Copper Mountain Technologies releases the new Planar 808/1 vector network analyzer, adding to its full size VNA line. CMT makes high performance PC-driven VNAs at an affordable price point without sacrificing metrological quality. Planar 808/1 is a four port VNA which operates with an external PC, opening a new range of possibilities for users who need highly accurate multiport instrumentation for lab, production, or field use. At just 19 pounds, Planar 808/1 is a more mobile and transportable solution than a traditional bench top unit. This lab quality VNA offers an extensive feature set, multiple data saving options, and is fully programmable for incorporation in automated applications.
Thanks to Asian Circuits
for Ongoing Support
Asian Circuits, with its HQ in Toronto, Canada, and production facilities in China, has emerged as a well known turn-key PCB assembly service provider. Asian Circuits is known for providing electronic manufacturing services, including PCB fabrication, components sourcing, and complete electronic assembly. Our online PCB assembly quote generator can help you estimate the assembly cost of your PCB project. We cater to customers primarily located in the U.S. and Canada.
Linx FM Series GPS Rx Module
for High Position Accuracy
Linx Technologies announces its launch of the self-contained, high-performance FM GPS receiver modules. At just 15x13 mm in size, the MediaTek MT3339-based FM Series gives the module fast lock times and high position accuracy even at low signal levels. Very low power consumption helps maximize runtimes in battery powered applications, such as positioning and navigation, location tracking, marine, and asset management. Simultaneously acquires on 66 channels and track on up to 22 channels. The GPS receiver is completely self-contained and only requires an antenna.
RF & Microwave Magazine
Articles for October
The RF & microwave trade magazines have updated their online articles for October. Here are a few that might interest
- Analyzing the Role of Local
Oscillator Phase Noise in
Reciprocal Mixing, ACS
- 100W High Power Silicon PIN
Diode SPDT Switches,
- Next Generation Wireless:
Riding On the Back of
- Measure Vector and Area
with an Oscilloscope X-Y
Display, Arthur Pini
- How to Think in dB,
- Understanding Measurement
Uncertainties in Spectrum
Analysis, Bob Nelson
- Evaluate EDA Software for
a Wireless World,
Dr. Stephen Maas
- Beyond CMOS Vs. GaAs:
Pick the Right Technology,
Stable Microwave Oscillators
Long before digital communications was widely adopted, there was a great need for stable frequency-determining devices / systems. That is to say, low bit error rates (BER) for digital communications are not the sole motivation for oscillators with low short-term and long-term stability and low levels of jitter. One obvious need for precise frequency control is radar, in order for accurate ranging (the second 'R' in radar) and in the case of Doppler systems, for accurate radial velocity reporting and clutter cancellation. Those capabilities existed long before digital systems came online. Aside from radar, precise frequency was needed in order to reduce guard band width between assigned channel assignments, thereby enabling more broadcast stations (commercial and military) to coexist in an allotted frequency...
How to Be Funny at the Office
"29 Skills Every Founder Needs to Master" is the theme of the November 2013 Inc magazine issue. Topics such as "How to Do More of What You're Good at and Less of What You're Bad At," "How to Take a Fresh Approach to a Staid Old Business," and "How to Really Connect with Customers," are typical. I scanned over a few to see what the entrepreneurial business owners had to say about their experiences that they considered most to be useful. Then, I arrived at the last one, Tip No.29: How to Be Funny at the Office. This I had to read. Something just didn't seem right, though, as I progressed through the story. Take this passage from a Q&A session...
PMI Intros 250 MHz - 8.5 GHz
Low Noise Amplifier
Planar Monolithics Industries (PMI) introduces Model No. PE210R258R515SFFLM Rev. B, a 0.25 to 8.5 GHz, low noise amplifier with a small signal gain window of +9.0 dB to +13 dB. The noise figure for this unit is ≤4.5 dB max (valid from 0.5 to 8.5 GHz) and offers an OP1dB of +16 dB min. The operating voltage is +12VDC and the current draw is 300mA max. The unit is supplied with removable SMA(F) connectors in our standard PE2 housing.
The Electronic Iron Curtain
Whoa! Take a look at the RF feedthrough and lightning arresting choke on the feed line on the original Voice of America transmitter in Munich, Germany. Now that is serious stuff. This story from an early Popular Electronics reports on the extreme lengths to which the Soviet bloc went in order to prevent its countrymen from hearing radio signals broadcast by the Voice of America and other non-state-approved beacons. Quarter megawatt transmitters sent messages of freedom that could be picked up by even the most remote crystal sets that didn't have the advantage of amplification. Ground-wave, sky-wave, and short-wave jamming techniques were employed to ensure the only signal that could be received was a buzz-saw type noise. Not so long ago, and certainly in 1959, America was viewed as a beacon of freedom, both figuratively via word-of-mouth and underground newspapers, and literally via high powered...
Bendix Model 75P6U
1940s Era AM/FM Radio
RF Cafe contributor Bob Davis has added another vintage radio to his collection - a Bendix Model 75P6U AM/FM tabletop radio. More extensive restoration is planned, but for now just replacing all the electrolytic and wax-paper type capacitors put the set into working order.
Challenging the Chip: Labor Rights and Environmental Justice in the Global Electronics Industry, by T. Smith, D. Sonnenfeld, and D. Pellow. I've never been one to shy away from a good argument when it comes to bucking against the ill winds of political correctness. In general, PCness causes the vast majority to suffer for the benefit of a relative few who often assert their 'rights' (real or imagined) to special privilege out of spite and/or self-righteousness. The subject of exploitation of the world's poor and desperate to the advantage of the rest of us bothers my conscience in a conflicted manner. On the one hand I realize that the exploited often consider their new conditions to be better than what they previously endured, but on the other hand there is a moral obligation to not rationalize away our complicity in the matter. The most egregious offenders are those who make a lot of noise about profiting from the misfortunes of said poor while obliviously...
A Lost Art: Wire-Wrapping
For this week's Featured Book, I wanted to find something on wire-wrapping. Although I was not successful at finding a book currently in publication that is dedicated to wire-wrapping, I did find a great page on Wikipedia full of information and great high-res pictures. There are plenty more resources if you do a Google search. Wire wrapping (w/w) used the be a very popular method for prototyping circuits when DIP and SIP packages dominated the electronics landscape. If done properly where wraps were placed on posts in order to make changes easier and where care was taken to avoid crosstalk from long parallel signals runs, w/w was useful at frequencies into the tens of megahertz, even with digital circuits. I personally have wire-wrapped more than a hundred boards both as engineering prototypes and as deliverable assemblies for military equipment. A well-done w/w board...
Floating Data Center
Which came first, the chicken or the egg? The same can probably be asked of Google and the government's (NSA, CIA, FBI, DHS, and various other 3-letter agencies) need for a massive data collection capability that at first glance has the appearance of a benign private company. Even though Larry Page and Sergey Brin undoubtedly developed and built Google without any help from the Fed, their current intertwinings with every facet of government from low level agency personnel all the way up to the prez himself is unquestionable. You don't get that kind of access and wield such influence without giving up something in return - usually your honor and personal motto (in this case abandoning "Don't Be Evil"). We have all witnessed hypocrisy on the part of Google's executives in the form of a pimped-out Boeing 767 aircraft for globe trotting under the guise of eco-warrioring, along with special landing privileges at military installations. Add to that...
Thanks Much to everything RF
for Continued Support!
everything RF is a search engine for RF & microwave components. everything RF lists complete catalogs from various RF & microwave component manufacturers and enables engineers to search through them by specification. There are over 124,463 components listed from more than 281 manufacturers. Download datasheets, request quotes or contact the suppliers for more information via everything RF. Its Fast & Easy!
Notable Tech Quote
"Dual-band." - Response (referring to AM/FM) given by Ham radio operator when ask by policeman in Virginia what type of radio he had installed in his car (hat tip to RF Cafe visitor KA). Virginia DOT requires that "A vehicle displaying Call Letter License Plates is subject to inspection by DMV or any police officer to determine if the operator and the vehicle comply with the requirements." You must "Have operational transmitting and receiving equipment permanently installed in your vehicle." The specific wording requires Tx AND Rx equipment (AM/FM radio is Rx only and therefore might not qualify), but that could just be bureaucratic ineptness. Now thieves on the prowl for mobile rigs know exactly which vehicles to target for a guaranteed payoff. BTW, I also learned while researching details on...
Fiber Optics Amplifier Tutorial
This tutorial should be useful both as an introduction to fiber optic amplifiers and for learning more details on them. We believe that even people already having a substantial experience with fiber amplifiers will find it helpful for deepening the understanding. The focus is on the underlying physics and the resulting technical consequences; we do not simply treat a fiber amplifier as a “black box”, but rather look inside. By RP Photonics Consulting GmbH.
Mozilla Lightbeam - Shining the
Light of Truth on Websites
A couple years ago, Mozilla published an add-on tool called Collusion for monitoring which websites were tracking your movements around the Internet. A follow-on app named Lightbeam, with even greater power, has been released: "Shining a spotlight on online data tracking to help people understand the Web around them." As with Collusion, Lightbeam gives you a picture of all the websites that are notified of your presence on your targeted website. For instance, when you evaluate RF Cafe using Lightbeam, you will discover that Google and DoubleClick (a Google subsidiary) are notified in order to serve pay-per-click banner advertisements. I depend on them to generate revenue for putting food on my table and a roof over my head. To be honest, I have no idea what happens after Google checks in, other than being fairly confident that the NSA is also notified as they are for every click, e-mail, or phone call you make anywhere...
Puzzle for 10/27/2013
This week's crossword puzzle was constructed specially for the good folks in the engineering department of Brigham Young University (BYU). Event planner J.M. wrote to request the use of a crossword, and in response I created one for them. If you have a similar need, I will be glad to do the same for your group if I have the time. Enjoy.
Many thanks to Orbel
Once Again for Support
Orbel Corp. is the leading designer and manufacturer of RF Shielding and EMI/RFI Isolation Products for printed circuit boards and electronic enclosures. Orbel also specializes in thin gauge photo etched metal parts and precision metal stampings made from a wide variety of material options. We manage every aspect of metal stamping from design, prototyping, short to medium runs and high volume stamping.
Spartant Wideband Signal
Generator with USB Interface
Spartant has developed a new line of wideband RF signal generators that have a USB interface. Their initial products include two models: 25-6000 MHz and 25-3000 MHz, both featuring USB for control / power and both having a +13 dBm maximum output power with phase noise of -106 dBc/Hz @100 kHz offset @250-1000 MHz. As with most USB test instruments, the size is kept small (about the size of a deck of cards) by having the user interface reside in software installed on the user's computer. An Ethernet interface will be available in the near future. Spartant is a 3dea Technologies company.
Anyone Can Make
In today's throw-away society, most people would never consider attempting to repair a speaker if it were to develop a tear or a puncture. Why should you bother when a replacement is so inexpensive? Well, there are several reasons you might want to affect the repair yourself. First, the speaker might be integrated into the system in such a manner that replacing it would be difficult or even impossible. Second, some speakers are actually pretty darn expensive, especially large diameter models and high quality models regardless of size. Third, a replacement might not be available, as with a vintage radio or television. Fourth, maybe you just want the challenge and satisfaction of repairing the speaker rather than adding its bulk to a landfill...
Empower RF Requests Your
Presence at AOC 2013
Empower is pleased to be once again conducting a "live" demonstration of an ultra broadband (20 to 1000 MHz), high power (1 kW CW) amplifier platform which is housed in an industry leading 5U chassis. The fact that we are controlling this amplifier through a wireless connection and highlighting diagnostics and remote control features through an iPad is equally impressive and, we believe, also industry leading. Our live demonstrations throughout 2013 have been well received and, for us, a serious validation of the next generation amplifier platforms we have designed
New RF & Microwave Products
Into at EuMW - everythingRF
everythingRF has issued a newsletter highlighting some of the new items introduced at European Microwave Week. It is the largest event for the RF & Microwave Industry in Europe. This year, 2013, it was held in Nuremberg, Germany from the 6-11 October. There were over 200 companies that took part in the exhibition.
Please Thank JFW Industries
for Supporting RF Cafe
JFW Industries is a world leader in designing and manufacturing of passive RF components and application specific test systems. These components include attenuators, RF switches, and specialized test systems for use in the cellular, telecom, OEM test equipment, medical, automotive, defense, and automated test systems markets. Application specific designs are the cornerstone of JFW's continuous technical advances in RF components
Measuring Peak and Pulse
Power w/USB Power Sensors
As technology and measuring techniques advance, the time eventually comes when continuing to use old methods not only doesn't make sense, but can actually harm your reputation by providing data that cannot be duplicated by customers who long ago adopted the new ways. Orwill Hawkins, of LadyBug Technologies, has written a white paper describing how to make accurate, repeatable peak and pulse power measurements on waveforms using the precision of modern instruments that provide a graphical view of the entity being investigated. USB power meters provide an inexpensive means of obtaining high quality measurements and the benefits of a graphical display environment (on your computer) at a relatively low cost. I particularly like the use of the word 'mesial' in describing the midpoint of a pulse's rising and falling edges.
Device Input Parameters
with Vector Analysis
Joe Cahak, of Sunshine Design Engineering Services, has published yet another paper in his series on making RF test measurements. This article will cover a recent test experience that utilized some thinking about the test fixture, the bias requirements and the device mounting and special calibration offsets needed to de-embed the test fixture response from the device response within the test fixture. The device also had to have bias on several ports simultaneously. We had to establish a "reference plane" within the fixture, from which we can use the Vector Network Analyzer's Port Extension or Phase Offset to dial out the distance from our 1 port calibration reference plane to the point of short reference within the fixture. With this phase offset compensation we can then measure the device capacitance of the part...
AWR.TV Playing AWR's IMS2013
AWR Corporation has launched a fully redesigned AWR.TV portal directly from within its main website framework to enhance the viewing experience of AWR’s hundreds of demos and tutorial videos. The new AWR.TV platform now supports multiple platforms for ready viewing on mobile devices such as iPads, iPhones, and Android handsets/tablets. Recently added additions to the AWR.TV platform include AWR’s nine MicroApps presentations from IMS 2013.
Don't Lose Your Mobile Rig
"If the car is parked in a dark remote spot it is better to do the job where the car is. This is because auto burglary is a lesser crime than stealing the whole damn car." That remark was made by a 'former' thief who ostensibly gave up a life of crime after spending nearly two decades in the slammer for various infractions of the law. One of his specialties was breaking into cars to steal radios - AM, FM, CB, Ham, or whatever was available. Mr. X volunteered his insight for the benefit of QST readers who might want to take proactive steps to help minimize the chance of being a victim.
Thanks Again to Triad RF
Systems for Their Support
Your source for RF Front Ends, transceivers and amplifier systems that just plain work! Solutions for integrating high performance HPAs into sophisticated RF subsystems and systems without sacrificing efficiency and linearity. Please remember that DCH Systems merged with Triad RF Systems earlier this year.
Skyworks Front Ends Support
Broadcom 5G WiFi Platforms
Skyworks Solutions announced that its industry leading wireless connectivity FEMs are being leveraged by Broadcom for use in several of the company’s 5G WiFi solutions, enabling some of the fastest download speeds available in access points, routers, DSL/cable gateways, PCs, smartphones and tablets. Skyworks' complete 2.4 and 5 GHz 802.11a/g/n/ac solutions integrate the power amplifier, filter, power detector, T/R switch, diplexer and associated matching in an ultra-compact form factor, delivering all the essential functionality from the output of the SOC to the antenna.
Amateurs - Your Thoughts
May be Worth Money
During the Golden Age of Radio (admittedly a subjective term), electronics innovators were generally as likely to be hobbyists (amateurs) as they were to be professionals with college degrees. In fact, according to this open letter from Eugene F. McDonald, president of Zenith Radio Corporation, in 1939, his company recognized the fact that most of their best ideas came from amateur radio operators, and that their engineering staff was populated overwhelmingly with Hams. Accordingly, the letter was a solicitation to amateurs to submit their ideas to the company to give designers not just valuable technical information gleaned from real-world experimentation (aka the School of Hard Knocks) but also insight into what type of equipment the Ham world would like to have made available for sale. Wouldn't it be great to still see the foundational electronics brands...
Hams in Space
OK, I admit that the Hams in Space organizational patch caught my eye and that's why I'm writing about it. Their little ploy worked on me mainly because of its vintage design motif, but I'll be honest and admit there might have been another reason as well. "Hams In Space is one of the KD0HKD.COM Satellite Web Sites where you can learn how the Hams in Space Team can come to your Amateur Radio Club Meeting, Hamfest, or Event to provide a presentation on FM Amateur Radio Satellites!"
PMI Intros High Speed
SPST Switch for x-Band
PMI Model No. P1T-9D25G-90-T-SFF is a high speed, solid state, single pole single throw switch capable of switching within 20 ns. The frequency range is 9.25 GHz (±30 MHz) with >90 dB of isolation.
Microsoft Visio 2003 Inside Out
Visio is still a mainstay for generating Office-compatible engineering block diagrams and schematics. Its ability to be programmed for automation makes it even more valuable to the code-writing guru. Microsoft Visio 2003 Inside Out covers all the ins and outs that you'll need to know to exploit its powers and to learn clever tricks for usage. "This supremely organized reference packs hundreds of timesaving solutions, troubleshooting tips, and workarounds all in concise, fast-answer format. It’s all muscle and no fluff. Discover the best and fastest ways to perform everyday tasks, and challenge yourself to new levels of Visio mastery!"
Silvertone Radio Discovered
at Tony Packo's
If you happen to be a fan of the M*A*S*H television series from the 1970s, then undoubtedly you are familiar with Corporal Maxwell Q. Klinger's multiple mentions of his old neighborhood of Toledo, Ohio haunts - some manufactured and some real. His Toledo Mud Hens ball team, for instance, is real. Uncle Abdul (Klinger is of Lebanese-American descent) and his original wife Laverne Esposito (from the Hungarian side of Toledo) were obviously fictional; however, it was because of Laverne that Klinger was introduced to Tony Packo's Cafe - a real place. The Hungarian style hot dogs from Tony Packo's were tops according to Max. In fact, his mention on the television show launched Tony Packo's to stardom and to being a highly prized tourist destination. On Feb. 24, 1976, Jamie Farr (Klinger) put Tony Packo's on the map...
Problems Like Doctors
Dave Palmer has a good piece on the Design News website titled "How to Be a 'Doctor of Engineering' Without Going to Grad School" about how, according to input from his son who is in medical school, the diagnosis technique being taught to aspiring doctors is similar to the troubleshooting technique used by (in Dave's case) mechanical engineers to get to the root of problems that are reported by customers. Doctors, at least during their training phase, use a four-step process termed "differential diagnosis." The doctor first notes symptoms and medical history, then considers possible causes for the malady, then prioritizes the list according to likelihood, and finally tests his conclusions by applying diagnosis and curative techniques. The parallel to electronic as well as mechanical troubleshooting...
Firefox Add-On Inserting
Popup into Web Pages
Internet advertising has hit a new low in the last few months. I have been noticing that every time I use the Firefox browser that ads are constantly popping up as the cursor is moved around the screen - even on the RF Cafe website -- which does not have and never has had popup ads. The screen capture below shows what I was seeing on my own website (RF Cafe)! I am NOT responsible for any popups that you might get, and neither are any of my advertisers. A Google search about the issue turned up many complaints about the same type of thing, primarily on Firefox. It turns out that an add-in, which must have been installed stealthily with an upgrade, was responsible. I don't visit questionable websites, so there is little chance it was picked up in that manner unless...
Fiber Optics Introductory
Tutorial by RP Photonics
RP Photonics Consulting GmbH has published a tutorial "that can serve as an introduction to fiber optics; i.e., for learning basic of fiber optics, but it also helps to improve the understanding for people who already have a substantial experience with optical fibers. The focus is on the physics of wave propagation and its technical consequences. We do not go into mathematical details, but rather try to create an intuitive understanding of the operation principles – often by demonstrating certain effects with numerical simulations. The simulation and design software RP Fiber Power of RP Photonics is an excellent tool for such purposes and has been extensively used for this tutorial." [App Note page link]
Notable Techie Quote
Please Visit Anatech in
Appreciation of Support
Anatech Electronics designs and manufactures the industry's widest range of RF and microwave filters at frequencies up to 40 GHz, as well as power dividers, directional couplers, and many other product types. We specialize in standard and custom designs for commercial wireless, public safety, satcom, and defense applications, and we can meet stringent military environmental specifications.
It's a Man's Job
Behind That Microphone
Of course if you listen to any of the old-time radio broadcasts on the Internet, they are recorded version of shows made long ago. However, back in the day those shows were first performed live in front of microphones and recorded in a broadcast studio. With a cast of two or three or even more, the actors would voice their lines with as much talent and effort as those performing for movies. The crew usually included a group of people responsible for creating background sound effects like horses running, car horns tooting, airplanes buzzing by, and dogs barking. All was done real-time with split-second timing required to pull it off and sound convincing. Radio audiences were unaware of all the work required as they sat intently listening to the Adventures of the Lone Ranger and The Shadow. Behind the scenes were dozens of engineers and technicians tending local radio broadcasting equipment and all-important telephone lines used for synchronizing...
Obtaining accurate, reliable, and useful measurements of RF power in the forward (transmission) and reverse (reflection) directions requires careful selection of test devices and detection equipment. LadyBug Technologies has produced a white paper describing a method for performing reflection and transmission measurements using a power sensor and a directional coupler. It includes a discussion on coupler directivity and impedance match as a factor in measurement accuracy.
RF & microwave Crossword
Puzzle for 10/20/2013
Every Sunday I create a crossword puzzle using a word list that I personally created and added to during over a decade of making puzzles. All of the words are related to engineering, science, mathematics, chemistry, astronomy, etc. There are no numbnut clues about movie stars or clothing designers. Enjoy.
Polystyrene: Its Electrical and
Polystyrene has been commonly used in capacitors since long before I came on the electronics scene. Its widespread use in electronic and electrical components was first adopted in Europe in the 1920s, and then later became popular in the U.S. where scientists improved its characteristics and lowered its cost to where it could be found just about anywhere current flowed. In its present form, polystyrene can be easily bent, cut, turned, polished, melted, drilled and tapped - truly a versatile material. This article provides a brief introduction to polystyrene.
Reduction of Distortion and
Noise with Inverse Feedback
Feedback circuits seem simple enough intuitively, at least for simple systems. It is easy, though, for someone not comfortable with algebraic manipulations to arrive at the wrong conclusion for how a given feedback constant figures into the calculation. Such was the case with an article published in the ARRL's QST magazine, when many readers wrote to the author accusing him of making an erroneous claim regarding using feedback to cancel out an unwanted harmonic in an amplifier. The criticism turned out being justified. Here is a statement of the error and an explanation of the proper approach which was printed a couple months later.
FCC Spectrum Dashboard
The FCC (Federal Communications Commission) has a very useful website set up for finding information about who owns spectrum licenses around the country, and what spectrum is available in your county. The Spectrum Dashboard has four primary methods for searching spectrum in the United States. You can use the dashboard to find out how spectrum is being used and by whom. There is an interactive allocation chart like the big wall charts that the magazines used to give away, only the nice thing about this one is that it never goes out of date. Of course the flip side is that if you wanted to research the historical band allocations you would need to look elsewhere. From the main page you may perform the following searches. Be aware that the map does not display where the frequencies are licensed or being used...