Bandwidth a Myth? -- Should bandwidth be a primary component in the regulation of digital amateur radio communication and more broadly as a primary component in the regulation of any amateur radio mode? -- The basic idea of radio frequency regulation is that a station is allocated a specific (carrier or center) frequency and a surrounding range of frequencies for the modulation (i.e., intelligence carried on the carrier). For CW (“Continues Wave” or pulse) this is simple. The CW modulation is the carrier being turned on and off for the modulation (with some allowance for the fact that pulsed square-wave on-and-off carrier does occupy more frequency space than a simple unmodulated carrier). For AM (Amplitude Modulation) the carrier stands in the middle and the variable (audio) modulation being added above and below the carrier. SSB (Single Side Band) is AM minus the carrier and one side of the audio modulation. FM (Frequency Modulation or phase modulation) is moving the carrier off center in response to the modulation. This all can easily be graphed in Cartesian coordinates with frequency on the x-axis and amplitude on the y- axis for the paniscope display, or frequency on the x-axis and time on the y-axis for a waterfall display. [It is not necessary to digress into spreadspectrum or other more complex modulation modes for the purposes of this comment. It should be noted than when the time clock is slowed way down, frequency hopping spreadspectrum and trunk- ed radio systems reveal communication on preallocated frequencies being used.]
For most radio services, the license from the spectrum regulator gives the licensee access to one assigned frequency (plus and minus a modulation width and some guard band space) or several assigned frequencies. The user has a reasonable expectation from encroachment by other users. The assigned frequency can also be more broadly called a “channel” (especially in analog television with an audio and a visual element). Even cellular telephone allocation work as groupings of specific defined frequencies, even if this is invisible and no concern to the ordinary user. WiFi has its predefined channels. For the user of household television or AM-FM radio this channelization of broadcast and cable stations is shown in the ability to click up and down the “dial” from station to station, rather than the old pre-digital need to manually “tune in” AM and FM radio stations.
A large exception to this assigned frequency (or channel) world of spectrum governance is the Amateur Radio Service. Amateur radio is given numerous broad bands of radio frequencies to be shared by all licensed operators/stations (subject to level of operator license and some division by type of modulation). In many ways, it is similar to the old fashion telephone party line with no one amateur or group of amateurs having any legal claim to any particular frequency spot. Day-to-day amateur radio works with common courtesy and acceptance of a fair amount of interference from nearby radio signals of other amateur radio stations a little higher or lower in frequency. Courtesy includes listening on frequency before transmitting, avoiding deliberate interference or prolonged monologues, and having a clean signal that does not splatter up and down the band.
The allocation of numerous broad bands of frequencies is also rooted in the radio experimenter history of amateur radio which continues today and into the future. By the use of different radio frequency bands the amateur can explore the still not completely charted word of radio propagation (including interaction with the not fully understood variable of weather, seasons, and the sun cycle). The amateur radio operator is free to explore new types of radio modulation – which is the basis of this RM-11708 filing to allow for more freedom is possible digital (non-voice) modulation signals. Other licensed radio services limit the user to a specified type of modulation and narrow channel or channels for a specified use, and essentially prohibit experimentation by the user. The heart of the traditional regulation of radio spectrum is to narrowly limit the user, form of modulation, and to specific frequency or channel (frequencies or channels). [The extent of detailed regulation is less in style in the age of mandated “frequency actions” but still exists in the qualification for possible bidders in the actions and industry standards for equipment that is eventually used.] Even in the experimental and developmental radio service, the applicant is require to carefully explain the planned use and licenses are granted for only a limited period of time.
The amateur radio operator is much freer to do their exploration and work out their evolving ideas over time than other licensed radio services. Amateur operators can build and repair their own equipment with minimal restrictions. Only the amateur radio operator has a VFO (Variable Frequency Oscillator) dial on his or her radio transmitter/transceiver – everyone else has equipment locked into a predefined channel or multiple channels. Most non-amateur radio users have no idea of what radio frequency they are using or how box they are using works on the inside. The non-amateur uses type accepted (etc.) boxes and they can not open up the equipment and do their own repairs and modifications.
To be honest, the typical amateur radio operator is not a white lab-coated scientist or on the trail of some Nobel Prize winning world-changing discovery, but their day-by-day operation does add their skill and knowledge of Hertzian wave phenomena and electronics. …
To get more directly back to the subject at hand of RM-11708 and “Bandwidth a Myth?” The amateur radio operator is limited to the amateur radio band frequencies and transmitter output power appropriate to his or license (or control operator’s license, to be technical).
The amateur radio operator license and the amateur radio station (e.g., call sign) is NOT limited in the number of transmitters that they can have on the air at any one time. Amateur radio club stations frequently have multiple operating positions and transmitters. The American Radio Relay League (ARRL) uses this type of setup at their station W1AW to send code practice and bulletin transmissions on a regular basis. Even an ordinary amateur can be using a HF (high frequency, short wave) transceiver while talking on the side over VHF-UHF walky-talky, for two transmitters. The FCC rules do not prohibit one amateur operator from having two transmitters with one on the 80-meter amateur band and the other on the 40-meter amateur band, both being keyed at the same time. And this number of transmitters is not just limited to two for any amateur radio license. In the commercial and military point-to-point services, his is called “frequency diversity” to help get message through 24-7 despite the variability and unpredictability of radio wave propagation at any one frequency (including phase fading and possible interference). With enough resources, the amateur could do the same, including sending parallel emissions from two transmitters on the same band (i.e., on 80-meters using both 3.510 mHz and 3.590 mHz. (This point will be further developed later in this comment and related back to regulation by bandwidth for the Amateur Radio Service.)
Another fact is that on-the-air regulation of radio signals does not really care how the signal was generated inside the originating station’s equipment – only the result being emitted from the originating station’s antenna. Whether the modulation (intelligence) is applied at a low level and then amplified through several stages before being emitted by the antenna or is applied at a high level in the final stage connected to the antenna in the transmitter makes no difference to the spectrum regulator (or to the person at the receiving end). It is not how it is done but the resulting radio signal emitted by the antenna.
Traditionally, a CW signal was generated by tuning on-and-off some stage of the transmitted while sending the letters and message. Over the air, there was the carrier signal present or not present for CW. For RTTY (Radio Teletype) the transmitter frequency was shifted between two set frequencies, usually 850 or 170 Hz apart in amateur radio practice. RTTY could be generated by two transmitters, one for each frequency care that one transmitter could be keyed at any one time, the easier approach was to shift the low level transmitter’s oscillator between the two frequencies and amplify this signal. The over-the-air result was the same and the receiving station could not tell the difference between the two transmitters or one shifting transmitter. The regulator did not as long as the over-the-air signal was the same.
In recent years (since the 1950s) there has been a change with the ready availability of amateur radio SSB (Single Side Band) transceivers. The SSB transceivers were originally developed for voice communication. The more efficient 3 kHz SSB voice signals have pushed aside the older 6 kHz wide AM voices signals from regular use on the HF amateur radio bands.
This widespread acceptance of SSB voice transceivers has also changed digital transmissions in amateur radio.
A digital radio signal can be created by adding a tone or tones into the audio input of a SSB transceiver. Disconnect the microphone and connect a tone source (i.e., modem) to the SSB transceiver and the antenna can emit a digital signal. A keyed single tone provides a CW signal. A variable or multiple tone generator provides RTTY or other digital mode. This SSB signal is limited by the transceivers voice filters to 2.5 to 3.0 kHz audio bandwidth.
This made digital modes of transmission available to may more amateur radio operations who already owned a voice SSB transceiver. They did not need specialized equipment for digital transmission, at least not in terms of the basic transceiver. Also, this is an increasing tendency for commercially available SSB transceiver to include some basic digital modes (RTTY, PSK31) in addition to voice and CW as standard equipment. Plus most SSB transceivers include an “auxiliary” socket for connection to a computer in addition to the normal microphone socket.
Second, the availability of home personal computers has changed amateur radio – along with most of the rest of the world. Software and the sound card in the personal computer could be used to generate the tones need to feed the SSB transceiver for transmitting a digital signal. Of equal significance was the ability of the personal computer software and sound card to decode the digital signal from the other amateur radio station. In the past this had required something like a Model 15 mechanical teletype machine and an interface (TU. Terminal Unit) connecting to the transceiver. Now it can all be done inside the PC. The message is typed on the personal computer keyboard … and the reply is seen on the computer screen. In between is the tone generating computer sound card, the amateur radio transceiver, antenna, and the radio signal flying to and fro through the air.
The result has been a big change in amateur radio operation. Voice is still the most popular with HF SSB and VHF/UHF FM with repeaters, CW with a hand key or bug still has its following, and digital keyboard-to-keyboard operation is growing day-by-day. There is experimentation (and a little equipment) for digital voice in the amateur radio ranks, too.
So much for history and what is happening today in amateur radio.
In RM-11708 the ARRL is trying to liberalize further the narrow retrains placed on digital communications in the Amateur Radio Service.
Sorry, a little more history. My understanding of the reluctance of the Federal Communications Commission to allow free experimentation by amateur radio operators in digital codes and modulation schemes, or for that manner any form of coded communication, goes back to the requirement that all amateur radio communication be in the open or clear. That amateur radio communication not be commercial in nature or any type of “spy” transmission. This required that the Federal Communications Commission’s Radio Monitoring Stations be able to receive and readily understand the content of Amateur communications. This is simple for Morse code (International or American) and voice communication. For RTTY, it required that amateurs be limited to the (mechanical teletype) equipment that was available at the FCC Monitoring Stations. Over time, the amateur radio rules were somewhat liberalize for common digital codes and relatively slow character speed (i.e., bandwidth).
In a few words, technology and the world of telecommunications has moved on, while the FCC Amateur Radio rules have lagged. This is not where amateur radio should be bringing up the rear guard of technology. Rather, amateur radio should have the freedom to be in the advanced guard of developing technology, and even exploring what may or may not be practical in the future. Amateur radio is a STEM playground with the least possible number of restrictions.
The idea has been floating around that the individual MF and HF amateur radio bands should be divided by modulation bandwidths rather that the present non-voice and voice division. Actually non-voice CW is allowed through each of the bands and voice is limited to the upper (higher frequency) portion of each of the bands, but it is easier to think in term of non-voice (exclusive) and voice segments. Non-voice and voice can more abstractly viewed as narrow bandwidth modulation and wider bandwidth modulation. This traditional non-voice and voice divide is less clear for modern digital modulations schemes that do not care whether the intelligence they are carrying is a off- on CW tone, telemetry tones, keyboard characters, facsimile, pictures or video, or digitized voice. The interim solution has been to consider keyboard communication as being more like narrow band CW and for video and digital voice to be treated as the wider band voice signals. To say that keyboard digital communication is narrow banded implies a slow character transmission rate. While keyboarding words per minute typing is limited for even the best typists, this is not true where a person can type a head while receiving the other person’s transmission, allowing the use of macros to save typing, or the message is a prerecorded file. The rapid transmission of a file (for example a listing of names of 200 people at an emergency shelter) requires bandwidth and is not practical as an HF radio digital signal, using todays amateur radio rules. Bandwidth used by digital signals is less dependent of the type of intelligence (data, picture, voice) than the symbol rate that it is being feed through the system. The ARRL quickly stepped back from the wording of its original RM filings and the implication that it applied to more than just allowed bandwidth for digital communications in the non-voice segments of the HF bands. This a fair reading of the current ARRL RM filing but not the possible direction for two or three RMs down the road.
Any eventual FCC rule making proposal and eventual order should make it clear that it is limited to increasing bandwidth/symbol rate for HF signals within the existing non-voice subbands, and not the larger issue of the better allocation of CW, digital, and voice communication in the amateur radio HF bands or that the HF band should be allocated simply on the basis of bandwidth of the individual signals in an evolving Amateur Radio Service. The rule making and order is limited and not precedent for the future course of Amateur Radio spectrum subband allocations.
Is it possible to limit amateur radio by the use of bandwidth limitations?
First of all amateur operators are limited by the existing band allocations (e.g., 3.5 to 4.0 mHz, 7.0 to 7.3 mHz., etc.). This is true down to at least 50 or 60 dB and the bandwidth of tank circuits, even if the math says that there are many side-waves going out from any modulated radio signal.
Second, over modulation, key clicks, splatter and noise is not what is being address in this comment or for any properly modulated RF signal or mode of RF communications.
Since a license amateur radio operator can operate multiple transmitters, even within the same amateur radio band and in close frequency proximity, a bandwidth limitation has little meaning. If an amateur operator can transmit a signal on 3.510 mHz and on anther transmitter on 3.590 mHz, at the same time or alternately (see above), or 3.510 and 3.525 mHz, which would be viewed as a 15 kHz wide signal for the purposes of RM-11708. This 15 kHz signal could be accomplished by using the two transmitters OR by the use of a suitable SSB transceiver modulated with a 1 kHz and a 16 kHz audio tones. The over the air result is the same whether the HF signal is created with two spaced HF transmitters -or- one HF SSB transceiver feed with two AF tones. The result is the same. Two frequency spaced transmitters or one SSB transceiver feed two audio tones, the over the air result is the same. So much for the idea of regulation by bandwidth in the Amateur Radio Service.
Along with many other amateur radio operators, I support the intent of the liberalization of the Federal Communications Commission rules, as proposed in RM-11708, but have some reservation about the use (and eventual enforceability) of an RF bandwidth based criteria in the context of the Amateur Radio Service.
Submitted by: James E. Mc Shane, WA0LHC 38 Ventnor Dr. Edison, NJ 08820