The Planned Regulation of Subbands by Bandwidth

By Bob Lewis (AA4PB)

Quite a number of hams appear to be concerned that the ARRL's proposed change in regulation would cripple ham radio by placing bandwidth limits on our signals. After carefully reading the proposal, it appears to me that the only limit is at the upper end of 3Khz for most of the HF spectrum. There is an exception to permit AM operation up to 6Khz bandwidth. For those who think this limit is unreasonable, I have to wonder if we really want modes that take up more than 3Khz of HF spectrum. In practice we have those limits now because we are limited to certain modes and a requirement to limit bandwidth to that prescribed by good amateur practice for the particular mode. To me that means that a SSB station operated in accordance with good amateur practice would certainly be limited to not more than 3Khz of bandwidth.

Some are concerned that we will somehow be required to be able to measure our bandwidth in order to ensure it meets the prescribed requirements. That will not be necessary for the majority of people. We have power limits but only those that operate at the limit have to actually measure it. It is not necessary to constantly measure the output power of a 100W transmitter to ensure that it doesn't go over 1500 Watts. We aren't required to have a frequency standard to measure our transmit frequency. We just stay far enough inside the band to be safe. In the digital realm there are presently requirements for some stations to stay within a 500 Hz bandwidth. Those stations are not required to demonstrate that to the FCC. It is accepted that the mode is 500 Hz or less. The same would be true if the proposed regulations are enacted. If you operate SSB with a properly adjusted transmitter then it would be assumed that you are less than 3 KHz wide and permitted to operate in the 3 Khz subband. The 60M band currently has a bandwidth limit of 2.8 Khz and we aren't required to measure our transmitters with laboratory equipment before we operate on 60M. The only people that would need the capability to actually measure the bandwidth would be the developers of a new mode that approaches the 3 Khz limit (or the limit of the subband they wish to operate in). I would hope that they would have measured the bandwidth of their signal anyway before they put it on the air. Once the bandwidth of the mode has been determined then the average user will not need to measure it. He will operate in the subband that has the bandwidth to accommodate that mode.

The 200 Hz subband is intended to permit CW at all speeds that a human operator can copy. ARRL tests show that 150 Hz is adequate for most CW signals. Yes, if you send a string of dits at 60WPM it may indeed exceed 200 Hz. I have to wonder why it would be necessary to send a continuous string of dits at that speed. If that's what you want to do however then you can simply move up to the 500 Hz subband. Hi speed computer generated and decoded CW may exceed 200 Hz as well but it will be permitted in the 500 Hz subband.

Why is it necessary to change the regulations to divide the bands into subbands to contain signals of like bandwidth? The present rules were written at a time when everything was analog. The bands were divided to group stations of a similar bandwidth together but they were prescribed by mode rather than the actual bandwidth. That used to work just fine. Phone was AM and SSB and image was analog slow scan, all of which has a similar bandwidth. They were grouped together in the high end of the band. CW and RTTY were much narrower bandwidth and so they were grouped together in the low end of the bands. With the rapidly changing technology the lines are becoming blurred. It is now possible to send almost anything via a digital means. The day is likely coming when you will be able to send voice, pictures, and data files over the very same digital signal. As the rules stand now you'd have to move to a different subband to transmit a different content, even though the signal is exactly the same. Then there are issues such as if I send my voice via a digital transmission is that phone, belonging in the phone subband or is it digital, belonging in the digital subband? With the present rules every time a new mode is developed there is the issue of whether the rules permit it at all. The FCC has “bent” many of the current rules to permit new modes to be utilized but you still find much of the experimentation being done outside the U.S. because our rules are no longer clear. Packet, for example, was not permitted in the U.S. for quite a while. This resulted in most of the early work being done in Canada. The FCC finally “bent” the rules by deciding that since ASCII characters were imbedded inside the packets then it was permitted under the rule that allows ASCII to be transmitted. PSK31 (also developed outside the U.S.) required even more of a “bend” since it transmits a different code entirely. The FCC finally ruled that since the new characters are translated from ASCII it too could be permitted under the rule that allows ASCII to be transmitted. Under that thinking I guess any mode that is typed on a computer keyboard can be considered ASCII since it began life as an ASCII character, regardless of how it was altered before being transmitted.

I believe the FCC is open to permitting new modes and experimentation. It is just that they are tied down by old, cumbersome rules and bureaucracies move slowly. The FCC actually proposed moving to assigning subbands by bandwidth some years ago but it never made it into the regulations.

By moving to assigning subbands by the bandwidth of the signal, every mode (including new modes yet to be developed) gets a place determined by its bandwidth. We no longer have to be concerned with having the mode authorized by the FCC before we can use it or experiment with it. The FCC no longer needs to “bend” rules to permit new modes to be used. It no longer matters what the content of the transmission is. All we have to do is put it in the appropriate slot for its bandwidth. Rather than imposing an additional burden on amateurs it will free us to experiment by accommodating new modes automatically. The rules will become much clearer and no longer require “liberal interpretation” to permit some of the existing modes.

In addition, the ARRL has done a good job in proposing bandwidth assignments that will have very little, if any, impact on any existing operation. If the proposed rules are enacted you will not have to move to a different band segment. Most of us can continue to operate exactly as we do now.