Category Archives: RF communications

Shortwave broadcasting is dying

I notice that many governments are cutting back if not shutting down their shortwave radio broadcasting operations. Shortwave radio and newspapers are both carriers of content, and both are affected by the Internet. Here’s a video from 2012 about Radio Netherlands closing its Caribbean shortwave broadcast station:

Putting all their eggs in one basket

I think that these broadcasters are shortsighted.

Providers of audio content argue that it’s cheaper to distribute their programming via the Internet. They forget that the Internet comprises many routers that reside in many countries. If a government decides to erect a firewall such as the Great Firewall of China, selected content can be blocked within that government’s jurisdiction.

One beauty of shortwave broadcasting is its simplicity. The entire shortwave route consists of only two stations: the transmitter and the receiver. Radio signals don’t respect national borders and radio jamming is expensive and never 100% effective.

In my opinion providers of other HF (high frequency: 2 to 30 MHz) services are also shortsighted, for the same reason: they’ve done away with their users’ backup systems. AT&T killed its high seas HF radiotelephone service, so now ships at sea depend solely on satellite links for shipboard telephone service. They have no backup. Ditto Loran-C: ships depend exclusively upon the GPS system for electronic navigation.

Articles:

  • November, 2014: Does Shortwave Radio Have a Future?
  • August, 2010: Whatever Happened to Shortwave Radio?

    For all its transmission expense and audio problems, analog shortwave radio has one clear advantage over the Internet and domestic radio/TV: It cannot be easily blocked — even when states try to disrupt its signals using jamming transmitters.

    Webcasts can be filtered or blocked through IP geolocation techniques that block access to sites based upon the IP address of the site or the user.

John Lennon: Gimme Some Truth:

Assume nothing.

In the 1970s, I worked in west Africa on a variety of radio communication systems. One day I was told that the Nigerian Navy’s base in Calabar was unable to communicate with its ships at sea. Apparently their HF (high frequency, 2 to 30 MHz) kilowatt amplifier had failed. I was told nothing else about the problem.

Lack of detail was normal. Communication and travel then in most of Africa was difficult. I grabbed a Simpson 260 VOM (volt-ohm-milliammeter), a standing wave bridge, a small toolkit, service manuals, and headed to the airport. The 500 mile trip by air to Calabar went smoothly.

Nigerian Navy NNS Thunder
Nigerian Navy NNS Thunder
When I arrived at the Navy base, I was shown to the radio room, where new HF SSB (single sideband) transceivers and a kilowatt linear RF amplifier waited. The operators demonstrated low receive signal strengths and when they tried to transmit, the amplifier immediately turned off its output stage’s plate current high voltage power supply.

I removed the coaxial cable feedline from the final amplifier’s output connector and replaced it with a dummy load. The amplifier behaved normally. I measured the resistance to ground of the coaxial feedline’s center conductor; it was a few Ohms. This is not necessarily bad; antenna couplers and some antennas with a DC path to ground will display a low resistance to ground, but for most antennas, it indicates a problem with the feedline or antenna.

Check the simplest possible failure point first

I asked to see the antenna. We walked to a nearby field, and — guess what? The antenna was lying on the ground!

Problem solved, or at least we knew what was wrong. I wish that all problems were so easily solved.

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© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Cel-Fi LTE signal booster

T-mobile works fine for me, except in my house. I think that the nearest T-mobile cell site is about a half-mile away, but the signal path is filled with old growth (signal absorbent) trees. I can’t use my cell phone on the ground floor, and it’s usable in only a few spots on the second floor.

Neither T-mobile’s tech support people nor its store personnel have helped. I read that T-mobile is now providing “signal boosters” to customers with weak signals in their homes. Apparently AT&T and other carriers offer similar systems.

CelFi LTE booster from T-mobileOn Friday, I fetched a new T-mobile “Personal CellSpot 4G LTE Signal Booster” from the T-mobile store, after paying a $25 deposit.

My booster is the “Cel-Fi” model RS3 or DUO, manufactured by San Diego-based Nextivity. It consists of two small boxes — the window unit and the coverage unit — and their wall wart power supplies. The window unit receives T-mobile’s LTE or HSPA signal (presumably at 1700 MHz), demodulates it, and transports the data via a 5 GHz unlicensed UNI link to the coverage unit. I placed the window unit on the second floor and the coverage unit on the ground floor.

cel-fi system schematic in house

What is its theory of operation?

Apparently the system is essentially a repeater. I have no idea how completely it demodulates the tower’s signal before creating the in-house signal. Is the in-house signal that’s transmitted by the coverage unit on the same frequency as the tower’s signal that’s received by the window unit? I don’t know, but I doubt it. Nextivity merely states that the coverage unit “cleans up” (whatever that means) the signal. Neither unit has any user interface other than some front panel LEDs.

Does it work?

Placement of both units is critical. I needed about an hour to get the system working throughout my house. Without field strength measurement instruments, I relied upon the limited information that’s provided by the units’ front panel LEDs. It works.

I’ve found almost no technical information about this system except a bit in a thread on Howardforums and a press release regarding Nextivity’s use of 1/4 and 1/2 Watt output power amplifiers in this product. If you have technical information — especially antenna radiation patterns — on this product, please let us know.

What if it quits working?

Occasionally (maybe once a week) the received signal from the Coverage Unit drops to one bar and/or my phone reverts to a slow EDGE connection. I’ve found that resetting the Cel-Fi system restores signal strength and LTE speeds at my phone. Follow these steps, in sequence:

  1. Remove power to the Coverage Unit
  2. Remove power to the Window Unit
  3. Wait 30 seconds
  4. Restore power to the Window Unit
  5. Restore power to the Coverage Unit
  6. Wait a few minutes while the two units establish a good wireless link and the Coverage Unit adjusts its output level

You should eventually see a full 5 bars received signal strength at the phone.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Is radio and TV broadcasting doomed?

The FCC plans to meet with broadcasters with a view to recovering some radio frequency (RF) spectrum from them. Recovered spectrum would be auctioned to cellular wireless broadband Internet service providers.

From a spectral efficiency viewpoint, this could make sense. Today’s modulation methods conserve spectrum (compared to traditional AM and FM broadcast signals) and the cellular model allows many geographically separated users to independently share one frequency. The packet model leaves each channel available for others whenever data isn’t flowing. From a consumer’s point of view, it allows program content on demand, rather than only when the broadcaster airs the content.

I wonder how much longer the RF broadcast model will make sense?

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

How mobile phones reveal your location

Obviously, when your phone’s GPS receiver is on, your location within 30 feet or so is usually available.

Cellular antenna system on monopole
photo Steve Kazella

There’s another way that remotes, your cellular service provider, 9-1-1 call centers [also known as Public Safety Answering Points (PSAPs)], and law enforcement can determine your phone’s location, even when your GPS is off, or even if your plain-Jane flip-phone has no GPS receiver. It’s called Uplink-Time Difference of Arrival U-TDOA). Here’s a brief simplified video description. Each cell tower has an antenna array with three or four 90 or 120 degree (when viewed from above) antenna sectors. Each tower knows, by comparing your phone’s received signal strength in each sector, which sector your phone is in. By measuring the propagation time for a “ping” to travel between the tower, your phone, and back again, it also knows the range to your phone. In a populated area your phone is likely to be talking with more than one tower, so all that’s needed is to know the bearing and range to your phone relative to two or more towers, and your location can be estimated within maybe a 100 foot radius. (You will be at the intersection of the two or more arcs.)

Even with only one tower talking to your phone, it knows that you are located somewhere along that 90 or 120 degree arc within the sector with the strongest signal. U-TDOA is used in Enhanced 9-1-1 Phase II systems so that first responders may be dispatched to wherever your cell phone is located when you place a 911 call for emergency assistance.

The only way to stop this is to remove the battery from your phone. (Oops. Sorry, iPhone users.) Switching it off won’t stop the communication. Switching it to Airplane Mode will prolly stop it, but there are no guarantees.

Update Here’s a clear explanation of mobile phone positioning techniques.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

FCC considers co-mingling TV and wireless

The FCC is desperately searching for available spectrum for the growing wireless data market. It has set its sights on spectrum in the 600 Megahertz (MHz) band that until now has been reserved for television broadcasters. Both industries are concerned about interference: FCC Requests Input On Interference Mitigation. What else did we expect from an FCC that’s chaired by a lobbyist for both the cellular and cable TV industry organizations?

(Note the incorrect use of the word “methodology” throughout the referenced article and the FCC’s statements. “Method” is correct and saves vowels.)

Television broadcast stations typically transmit very high power six Megahertz wide signals. Because of their high frequency, the signals may be received within line of sight only. Presumably the FCC would oversee a patchwork quilt of shared spectrum, with some geographic areas having no available shared spectrum, while other areas would have plenty of available spectrum.

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© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

FCC’s Mobile Speed Test

The FCC has released a test version of a cellular data transfer speed measurement app for Android devices. It’s available from https://play.google.com/store/apps/details?id=com.samknows.fcc.

fcc-test-resultsThe FCC has published the Android app’s open source code on its Github site. They’ve promised an iPhone version. It’s being developed by Samknows.com.

According to the app’s FAQ, “the application will run continuously in the background, periodically performing measurements.” I’m not enthused about having this app running continuously. I’ll probably uninstall it after each measurement run.

A feature of this app that I like is that it collects and reports “cell tower ID” and “cell tower location code” — data that may help my quest to pinpoint the physical location of T-Mobile’s nearest cell site. It also reports received signal strength in dBm.

The speed test data are collected from your mobile device and aggregated by the FCC. Let’s hope that they use the data to hold the carriers’ feet to the fire.

One reported problem is that the app, when testing over a WiFi connection, thinks that it’s connected via LTE. Also, it may have contributed to problems I had with other apps today.

4G??

If you examine the screenshot, you’ll see that although T-Mobile claims that the wireless connection (which was HSDPA when I snapped the screenshot) is “4G”, the download speed is a wimpy 1 Megabit per second. This disproves T-Mobile’s claim that HSDPA+ is “4G”. (The ITU specifies that 4G system mobile phones have a minimum peak download speed of 100 Mbps.) Maybe the FCC or FTC will do their jobs and slap T-Mobile for false advertising.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

WLW: 1930s AM broadcast superstation

As entertainment delivery progresses from the broadcast model that was pioneered by David Sarnoff toward a content on demand model, it’s fun to stop and examine the roadside litter.

An impressive relic of the old broadcast days is the WLW 500,000 Watt transmitter located outside the city of Cincinnati. From 1934 until 1939, WLW broadcast a whopping 500,000 Watt AM signal on 700 kHz that covered North America from coast to coast.

Front panels of 500,000 Watt transmitter Photography by Frederick Vobbe, Lima OH
Front panels of 500,000 Watt transmitter
Photography by Frederick Vobbe, Lima OH

For most of its life, WLW transmitted 50,000 Watts, but in the 1930s it pumped out 500,000 Watts under a special authorization that needed to be renewed every six months. In 1939 Congress and the FCC reconsidered the wisdom of allowing a single station to control one frequency nationwide and withdrew the 500 kilowatt authorization. No other US AM station has ever been authorized to transmit more than 50 kW.

The 500 kW hardware was massive. Its final amplifier consisted of twelve water-cooled vacuum tubes with a plate dissipation rating that totalled 1.2 Megawatts. It was plate modulated by eight more 100 kW plate dissipation water-cooled tubes. This video walkthrough shows the oversized components that are still in place.

This excellent article on WLW in the 1930s claimed,

WLW was the 1930s version of NASA, continually testing the limits of just what AM broadcasting could do under U.S. regulation.

Powel Crosley, Jr. owned WLW. His factories produced radios, appliances, eventually TVs, and even cars. WLW provided the perfect advertising platform for Crosley products.

Today the tiny microprocessor, hair-thin fiberoptic strands, packet switching, media streaming, and especially content on demand technologies threaten the future of the once mighty radio broadcasting giants. Their giant carcasses remain as monuments, like the shattered visage of Ozymandias.

HySky HF wireless network

Here’s a novel idea: build a wireless network of low-power HF (High Frequency – 2 to 30 MHz) radio stations to collect and transport low-speed data from remote sites.

The license granted by the FCC to HySky Technologies is intriguing. It may be unique. It grants HySky limited access to 934(!) HF frequencies. HySky’s website claims that

HySky offers an attractive alternative where cellular coverage is unavailable or , the collection of sensor data via satellites is exorbitantly expensive.

HySky boasts that its HF network will be suitable for:

HySkylogo

  • Asset Tracking
    • GPS Asset Tracking
    • Inland Waterways
    • Geo-Fencing
    • Hazmat Tracking
  • Information Services
    • Alarm and Security
    • Citizen Emergency Notification
    • Digital Message Sign Control
    • RXR Crossing Monitoring
  • Remote Sensors
    • Rooftop HVAC
    • Flow and Power
    • Security Entry Notification
  • Homeland Security
    • First Responder Notification
    • Citizen Notification
    • Hazmat Tracking
    • Container Tracking

How HF signals propagagate

SpreadF-NPSHF signals behave differently than cellphone signals (which operate in the 700 to 1900 MHz range). HF signals can travel far beyond line-of-sight, either by hugging the Earth (called “groundwave”, a daytime phenomenon) or by reflecting from the ionosphere (called “skywave”). The biggest problem with HF is atmospheric and man-made noise. HF signal propagation varies not only hourly, but seasonally and as a function of the 11-year sunspot cycle.

One characteristic of HF groundwave propagation is that it is decidedly not line-of-sight: the signals permeate everywhere within a given radius. This may be an advantage relative to the directional characteristics of signals in the 700 to 1900 MHz range.

I’m going to guess that the HySky HF network will, on each link, dynamically try each of their 934 frequencies until the lowest signal-to-noise ratio (SNR) is found for that link. Apparently an out-of-band control channel will be provided by both subcarriers on broadcast FM signals and above 1 GHz signals via satellite.

HySky CEO Chief Executive Officer is Charles Maynard. I found this in Radio Ham develops HF asset tracking network:

To ensure maximum reliability, we continually test the propagation characteristics of our 954 FCC licensed frequencies within the HF radio spectrum using 44 low power transmission sites strategically located across the United States.

The mobile tracking units using this spectrum will transmit a maximum of 1 watt Effective Radiated Power using a small low- efficiency broadband antenna. The data will be received by nine stations located at low-noise [read: rural] sites across the USA which will then forward the data to customers.

An unusual network

HySky’s FCC license seems to be unique. It restricts the output power of each transmitter to 15 Watts maximum. Other license parameters: The radiated power of each HF transmitter and its antenna system(s) as typically installed must not exceed one Watt. The operational modulated emission type must be 2K80G1D. [Huh? I’ve never heard of 2K80G1D!] Maximum bandwidth is 3 kHz. The duration of each HF transmission by each transmitter must not exceed 4 seconds.

This is a very unusual system that’s now licensed and will presumably be constructed soon. I’d like to learn more about it, but can’t find many details. Can you?

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Wayne Green goes QRT

A few years ago I wrote about Wayne Green (Going Green), an influential and controversial editor and publisher of first Amateur Radio, and later, computer periodicals. Wayne had strong opinions about everything. I agreed with many of his ideas, but some of them just seemed nutty.

Going GreenAccording to a notice on Wayne’s blog, he passed away on Friday the 13th. Born in 1922, Wayne lived to be 91 years old. Many moving tributes have been posted on his blog since Friday. His enthusiasm and vision kick-started a lot of people in the technology sector. Rest In Peace, Wayne.

(QRT is a radio telegraph abbreviation that means “I’m shutting down operations. This station is going off the air.”)

February 2016 update: waynegreen.com is now owned by someone else. To read Wayne’s blog, view its “snapshots” on archive.org.

GaN technology is charging ahead

The IEEE just concluded its Microwave Symposium in Seattle. The star semiconductor material at the symposium was Gallium Nitride (“GaN”).

Monocrystal of gallium nitride
Monocrystal of gallium nitride

GaN semiconductors exhibit fast switching speeds and high voltage breakdown characteristics together with stable gain over a wide temperature range. A friend who attended the meeting reports that GaN is pulling ahead of the more traditional GaAS (Gallium arsenide) semiconductor technology. (Older light emitting diodes — LEDs — are constructed of GaAS. Most high-brightness LEDs are constructed of GaN.)

As manufacturers learn how to fabricate sub-micrometer GaN devices, we can look forward to seeing reasonably-priced portable gadgets that use still higher frequencies — 50 GHz and higher will be feasible at reasonable cost, thanks to GaN. Possible downsides are that precipitation and even water vapor attenuate signals at these frequencies, and propagation is strictly line-of-sight. As this technology matures, marketers will find applications to exploit it.

Because of its high breakdown voltage characteristics, electrical switchgear manufacturers are developing products that use GaNs to switch high voltage circuits as well(!).

There’s still lots of GaN development to be done, but it has great promise.

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© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Discerning reality

In the late 1960s I was part of a small product development team whose goal was the design of a frequency-synthesized radio receiver. This included a phase-locked frequency synthesizer whose output could be set to anything from 156 to 186 Mhz in 100 Hz steps. It used two VCOs (Voltage Controlled Oscillators — their output frequencies vary as a function of steering voltage). The output frequency of each VCO was determined by a phase-locked loop. It was the first time that our employer had developed a phase-locked loop frequency synthesized product.

Noisy oscillator signal
VCO output with noise sidebands
The frequency synthesizer’s high-speed VCO covered 30 MHz in steps of 1 MHz. We distributed the 30 MHz range amongst three oscillators, each of which covered a 10 MHz range. While prototyping, we discovered low-frequency noise sidebands on the VCO’s output signal. We needed to remove these noise sidebands, or they’d appear in the receiver’s output. On a spectrum analyzer, the noise sidebands appeared to be 20 to 400 Hz each side of the output signal and 15 dB below output signal level.

After selectively freezing circuit components while observing the noise sidebands, we learned that the carbon composition resistors in the loop filter were (one of) the culprits. GrainsThat was a surprise: I had always thought of resistors as discrete inert lumps. I learned that carbon composition resistors consist of tiny grains of carbon bound to tiny grains of ceramic. We were seeing noise caused by random molecular motion. These voltage spikes, though mere microvolts in amplitude, were modulating the VCOs, resulting in noisy sidebands on the VCO’s output signal.

We substituted carbon film resistors, and discovered that the noise sidebands dropped substantially. I learned that carbon film resistors can dissipate less power, but offer a more contiguous medium than ordinary carbon composition resistors. Once we’d peeled back this layer, we discovered that the ceramic feedthru filter capacitors that fed each oscillator with DC power were also modulating the high-speed oscillator.

Instrumenting this circuit was interesting: we couldn’t load the phase locked loop itself with instrumentation or the phase lock would fail; we could only examine the noise sidebands that were an effect of noisy phase locked loop components. Since those days, I’ve learned that often we can’t directly examine phenomena — we can only see indirect effects. I suppose that this is how astrophysicists have discovered dark matter. Dark matter doesn’t reflect or refract electromagnetic energy; it’s detectable only indirectly because it’s affected by gravity.

What do we ever know about anything?
B.F. Skinner was alternately praised and despised because his brand of psychology, which became known as behaviorism, admitted that it’s impossible to know the inner workings and hidden mechanisms of humans; we can only observe behavior. He had a point: are humans less mysterious than electron movements or dark matter? In the end, what do we know about anything or anybody other than its behavior?

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© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Smartphones’ impact on spectrum

Smartphones chew up rf (radio frequency) spectrum. Last month my Android phone, according to T-Mobile, consumed 15 gigabytes of data — and I don’t stream movies.

Randall Stephenson, AT&T’s CEO, recently expressed regret that AT&T offered iPhone buyers unlimited data for $30 per month:

My only regret was how we introduced pricing in the beginning, because how did we introduce pricing? Thirty dollars and you get all you can eat. And it’s a variable cost model. Every additional megabyte you use in this network, I have to invest capital.

Nobody foresaw the voracious data appetite of the iPhone.

FCC Chairman Julius Genachowski stated that a smart phone uses 24 times more spectrum than the predecessor feature phones, and a tablet uses 120 times more spectrum. Without taking action to find more spectrum for these devices, “we risk losing out on extraordinary commercial and social opportunities,” he said.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Some WCIT meeting attendees will try to constrict the Internet.

wcit-12 logoOn Monday, the United Nations’ ITU (International Telecommunications Union) will convene its twelfth World Conference on International Telecommunications (WCIT-12) in Dubai. Its last full meeting was in 1988. The meeting runs from 3 through 14 December. Government telecom administration representatives from 193 nations will attend. The ITU has traditionally concerned itself with telephone and radio spectrum allocation; now some governments wish to use the ITU to censor Internet communication. The U.S., like all 193 member nations, has only one vote on each proposal.

ITU logoFor decades these meetings went unnoticed by the general public, so nobody cared that meetings were closed and meeting documents weren’t available to the public. Now, some WCIT-12 documents appear on wcitleaks.org. Its News page contains links to fascinating articles that discuss the contentious issues posed by the growth of the Internet within repressive nations.

One item on the agenda is the demand that anonymity on the Internet be eliminated. Another would endorse Syria’s closing of access to the Internet. Dicatorships and kleptocracies fear the free exchange of information.

It appears that WCIT-12’s theme may be an attempt by nations with sketchy human rights records to wrest control of the Internet from its US-based roots. ICANN (Internet Corporation for Assigned Names and Numbers — it oversees domain names and IP addresses) is in their sights: Latest WCIT Leak Makes Explicit Russian Desire to Overturn ICANN:

According to the proposal, “Member States shall have the sovereign right to manage the Internet within their national territory, as well as to manage national Internet domain names.” And a second revision, also aimed straight at the heart of today’s multi-stakeholder process, reads: “Member States shall have equal rights in the international allocation of Internet addressing and identification resources.”

From “UN Agency Reassures: We Just Want to Break the Internet, Not Take it Over,” Forbes.com, Oct. 1, 2012:

Dozens of proposals secretly circulating ahead of the WCIT meeting would go well beyond usurping ICANN’s authority, and would if adopted introduce sweeping architectural changes that would allow the ITU and its members to redesign the Internet to something much more controllable.

Video interviews clip

Surprisingly objective brief Al Jazeera video summary of issues

The ITU’s blog may publish daily meeting updates.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

T-Mobile’s Deceptive Vocabulary

My Samsung Insight II phone includes firmware by T-Mobile. When near an up-to-date cell site, the little icon to the left of the signal strength indicator proudly displays 4G. T-Mobile Android desktop with 4G icon While I remain in the same location, when I check the phone status within the Settings app, Mobile Network Type is either UMTS or HSDPA.

Neither UMTS (Universal Mobile Telecommunications System) nor HSDPA (High-Speed Downlink Packet Access) is considered to be 4G (Fourth Generation), yet T-Mobile calls them 4G. UMTS and HSFPA are 3G technologies that enhance GSM. They’re pretty fast (I measure 3 Mbps download speed), but they ain’t 4G (potentially up to 50 Mbps).

Once again, T-Mobile has attempted to change the definitions of words. See recent article T-Mobile’s “Unlimited Plus” data plan.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695