KB6NU's Ham Radio Blog

KB6NU's Ham Radio Blog

digital

RadioWorld update on proposal to use HF for stock trading

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Radio WorldOver the summer, the amateur radio world was all up in arms about a proposal by an outfit called the Shortwave Modernization Coalition—which doesn’t have a website that I could find—that the FCC allow them to transmit high-power, wide-bandwidth digital signals between 2 MHz and 25 MHz. Comments were due by August 15, and RadioWorld has just published an update on the status of this proposal and the comments it garnered.

The article, “Hams Worry About Shortwave Proposal,” is a pretty good summary of where we are just now. Here are a couple of key quotes:

  • “AARL (sic) adds: ‘SMC also proposes to substantially lessen the protections required to protect adjacent and neighboring licensees … using digital schemes with 50 kHz bandwidths and 20,000 watts of power.’” If they want to transmit wide-band signals at such high power, they should be required to meet an even higher standard than normal for harmonic and spurious emissions. Instead, they’re proposing that the FCC loosen the specifications.
  • “Another commenter from the amateur community said the FCC’s ability to track and solve any possible interference issues is severely lacking.” If the FCC could be counted upon to act swiftly should these transmissions cause interference, then the interference might not be a big deal, but as the commenter notes, the FCC just doesn’t have the resources to do this.

Radio amateurs aren’t the only ones who have commented on the proposal. Perhaps our biggest ally in this matter is the NTIA, which is the government agency responsible for the development of communications policies that affect government operations. In their comments, they write, “To the extent the Commission considers initiating a responsive rulemaking, NTIA respectfully requests that the Commission recognize that much more information would be needed to ensure protection of the significant number of incumbent federal operations in the 2-25 MHz band.”

The comments then go on to detail all of the government operations that would be affected. They include the Maritime Mobile Service, the Aeronautical Mobile Service, and Federal Emergency Management Agency National Radio System (FNARS).

There are also comments from an SMC competitor. Alex Pilosov, founder and president of Shortwave Solutions says the coalition’s request “is premature, incomplete and poorly thought out, and against the public interest,” and that its “lack of substance is matched by its audacity.”

So, stay tuned. The SMC proposal faces a lot more opposition than just ham radio.

Notes from the ARRL Board Meeting, July 19-20, 2013

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ARRLI haven’t gotten the full minutes yet from the recent ARRL board meeting, but there’s a news story about the meeting on the ARRL website. Some interesting things were discussed:

  • ARRL to spend big bucks on Logbook of the World. The board voted to spend $75,000 on outside professional services to improve LoTW’s database. The Board also okayed the hiring of a full-time Headquarters staff member with “strong IT development and architectural skills” to address LoTW improvements. That seems like an awful lot of money to me.
  • ARRL will petition FCC to get rid of symbol rate references. Instead of specifying symbol rates in Part 97. 307(f) , the petition would ask the FCC “to apply to all amateur data emissions below 29.7 MHz the existing bandwidth limit, per §97.303(h), of 2.8 kHz.” I like this idea a lot. It will give hams the incentive to experiment with new digital modes.
  • New training materials.  The article notes that the Board “directed Headquarters staff to investigate the feasibility, benefits and costs of preparing license training materials designed for shorter course sessions.” Uhhhh, I’ve had those materials for many years now. Not only that, the PDF version is FREE! 

Extra Class question of the day: AC waveforms: sine, square, sawtooth and irregular waveforms; AC measurements; average and PEP of RF signals; pulse and digital signal waveforms

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We use all different kinds of waveforms in amateur radio. It is, therefore, important to know about the different types of waveforms and how to measure their parameters. One of the most important parameters of a waveform is its period. The period of a wave is the time required to complete one cycle. (E8A08) The frequency is the inverse of the period. For example, if the period of a wave is 1 msec, or .001 s, the frequency of that wave is 1 / .001s, or 1000 Hz.

Another parameter that we need to know about a waveform is it root mean square, or RMS, value. The root-mean-square value of an AC voltage is the DC voltage causing the same amount of heating in a resistor as the corresponding RMS AC voltage. (E8A04) Because of this, the most accurate way of measuring the RMS voltage of a complex waveform would be measuring the heating effect in a known resistor. (E8A05)

If the waveform is regular, it’s relatively easy to calculate the RMS value. In the case of a sine wave, the RMS value is 0.707 times the peak value. You use the RMS voltage value to calculate the power of a wave.

The type of waveform produced by human speech is, however, irregular. (E8A09), and  the characteristics of the modulating signal determine the PEP-to-average power ratio of a single-sideband phone signal. (E8A07) This makes calculating or measuring the average power more difficult.

If you know the peak envelope power (PEP), though, you can make a pretty good guess at the average power. The approximate ratio of PEP-to-average power in a typical single-sideband phone signal is 2.5 to 1. (E8A06) Put another way, the average power of an SSB signal is about 40% of the peak power.

It used to be that all the waveforms we used in amateur radio were analog waveforms, but digital waveforms may be even more important than analog waveforms. An advantage of using digital signals instead of analog signals to convey the same information is that digital signals can be regenerated multiple times without error. (E8A13) All of these choices are correct when talking about the types of information that can be conveyed using digital waveforms (E8A12):

  • Human speech
  • Video signals
  • Data

Perhaps the most common digital wave form is the square wave.  An ideal square wave alternates regularly and instantaneously between two different values. An interesting fact is that a square wave is the type of wave that is made up of a sine wave plus all of its odd harmonics is. (E8A01)

Another type of wave used in amateur radio is the sawtooth wave. A sawtooth wave is the type of wave that has a rise time significantly faster than its fall time (or vice versa). (E8A02) The type of wave made up of sine waves of a given fundamental frequency plus all its harmonics is a sawtooth wave. (E8A03)

Digital data transmission is one use for a pulse modulated signal. (E8A11) Narrow bursts of energy separated by periods of no signal is a distinguishing characteristic of a pulse waveform. (E8A10) The waveform of a stream of digital data bits would look like a series of pulses with varying patterns on a conventional oscilloscope. (E8A15)

To make use of digital techniques in amateur radio, such as digital signal processing or DSP, we must convert analog signals to digital signals and vice-versa. Sequential sampling is one of the methods commonly used to convert analog signals to digital signals. (E8A14) When converting an analog signal to digital values, an analog to digital converter measures, or samples, the value of the analog signal at different points, and converts that measurement to a numeric value. Those numbers are then input to a processor or directly into memory.

TAPR Conference Videos Online

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From the ARRL Letter, 1/12/12:

Amateur Radio Video News (ARVN) has released high-definition videos of all the talks presented at the 2011 ARRL/TAPR Digital Communications Conference (DCC), held September 16-18. The programs are now available online on the ARVN website.

The DCC is a three-day conference on Amateur Radio digital technology. Among the video presentations are 18 seminars, the Saturday Banquet and the welcome introduction by TAPR Chairman Steve Bible, N7HPR. According to ARVN Producer Gary Pearce, KN4AQ, most of the talks are fairly technical, although there are four separate sessions that cover “Intro to” topics. “All of the talks — except the ‘Intro to’ talks — were shot in three-camera high-definition, with wireless mics for ‘close-up’ audio of the presenter, as well as the question-and-answer period,” he explained. “The ‘Intro to’ talks were shot with a single, standard-definition camera.

This year, Pearce decided to release the programs on the web instead of the DVDs that have been produced in previous years (although the DVDs will be available later). “I wanted to make the programs available more quickly and easily to a worldwide audience,” he said. “The web has become an easy, high-quality distribution medium.”