Extra Class question of the day: modulation methods; modulation index and deviation ratio; pulse modulation; frequency and time division multiplexing

In FM modulation, the two primary parameters of interest are deviation ratio and modulation index. Deviation ratio is the ratio of the maximum carrier frequency deviation to the highest audio modulating frequency. (E8B09) The deviation ratio of an FM-phone signal having a maximum frequency swing of plus-or-minus 5 kHz when the maximum modulation frequency is 3 kHz is 1.67. (E8B05)The deviation ratio of an FM-phone signal having a maximum frequency swing of plus or minus 7.5 kHz when the maximum modulation frequency is 3.5 kHz is 2.14. (E8B06)

The term for the ratio between the frequency deviation of an RF carrier wave, and the modulating frequency of its corresponding FM-phone signal is modulation index. (E8B01) The modulation index is equal to the ratio of the frequency deviation to the modulating frequency. The modulation index of a phase-modulated emission does not depend on the RF carrier frequency. (E8B02)

The modulation index of an FM-phone signal having a maximum frequency deviation of 3000 Hz either side of the carrier frequency, when the modulating frequency is 1000 Hz is 3. (E8B03) The modulation index of an FM-phone signal having a maximum carrier deviation of plus or minus 6 kHz when modulated with a 2-kHz modulating frequency is 3. (E8B04)

Some amateur radio communications are pulse-width modulated. That is to say that the information being sent is proportional to the time the carrier is on. When using a pulse-width modulation system, the transmitter’s peak power greater than its average power because the signal duty cycle is less than 100%. (E8B07)

Some signals are pulse-position modulated. That is to say, what is significant is when the pulse occurs. The time at which each pulse occurs is the parameter that the modulating signal varies in a pulse-position modulation system. (E8B08)

Frequency division multiplexing is one method that can be used to combine several separate analog information streams into a single analog radio frequency signal. (E8B10) When a system uses frequency division multiplexing, two or more information streams are merged into a “baseband,” which then modulates the transmitter. (E8B11)

When a system uses digital time division multiplexing, two or more signals are arranged to share discrete time slots of a data transmission. (E8B12)

Military thinking about “wideband” sideband for datacomm?

Bob Brewin, editor at large, for  Nextgov,  a website that cover government IT, speculates about the use of wideband SSB to achieve higher data rates than is currently possible on HF. His column notes:

The Air Force High Frequency Global Communications System Program Office at Tinker Air Force Base is looking for some folks to help tweak single sideband so it can function as a relatively wide band over the air data transmission system as well as handle voice over IP. Single sideband will never have the throughput of a fiber optic connection. On the other hand, there’s not a lot of fiber drops in the sky or a forward operating base in Afghanistan, so a 120 kbps connection from a radio looks real good.

This certainly sounds like a project for some enterprising hams. And, who knows, this  new mode might even make its way into the ham radio bands someday.

Papers Requested for ARRL/TAPR Digital Communications Conference

Amateurs are invited to submit technical papers for presentation at the 31st Annual ARRL and TAPR Digital Communications Conference to be held September 21-23, 2012 at the Sheraton Gateway Airport Hotel in Atlanta, Georgia.

These papers will also be published in the Conference Proceedings (you do not need to attend the conference to have your paper included in the Proceedings).

The submission deadline is July 31. Please send papers to: Maty Weinberg, ARRL, 225 Main St, Newington, CT 06111. Or you can make your submission via e-mail to: maty@arrl.org.

For more information about the conference, see the Tucson Amateur Packet Radio www.tapr.org/dcc, or call 972- 671-8277.

TAPR Conference Videos Online

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.”

 

Yaesu thinks the future of ham radio is digital

A Digital Communications GuideYaesu thinks the future of ham radio is digital, and of course, that amateurs should adopt its digital mode (C4FM) over Icom’s (D-STAR). At least that’s what they say in their latest publication, A Digital Communications Guide for Amateur Radio Operators.

This publication claims several advantages for digital communications techniques, including:

  • reduced bandwidth,
  • digital data transfer,
  • better performance,
  • immunity to interference, and
  • product and system cost reduction.

It talks about some of the theory behind digital communications, explaining in relatively simple terms how the various modulation techniques work. Of course, it slams D-STAR:

Now, this method [GMSK] is considered old fashioned and no longer used by LMR [land mobile radio]. Currently, GMSK is still being used by D-STAR.

One problem I have with this publication is its implicit assumption that digital is better than analog, and that if we want to be “progressive” amateurs, we should all adopt digital communications techniques. I’m not all that convinced, and to its credit, Yaesu does concede that “analog FM can show an advantage over digital radio in some areas.”

I haven’t compared prices, but if the D-STAR radios are any indication, the prices of Yaesu’s digital radios are bound to be more expensive than the analog radios. I just don’t see that the added functionality is worth the extra cost.

What do you think? Do you think D-STAR or Yaesu’s C4FM will gain widespread acceptance anytime soon? Do you currently own a digital radio? If not, what would convince you to buy a digital radio?