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I know that the amateur bands are not channelized. I know that anyone can pick an arbitrary frequency and they're not wrong, and you are not obligated to have a calibrated VFO. But if everyone picks frequencies at random during a period of heavy usage, there's likely to be inefficient allocation due to not-quite-wide-enough gaps to fit in.

Do there exist, then, any conventions for what frequencies to use, that are more widespread than each individual operator's idea for best practice?

Thinking about this once, I said to myself: SSB is 3 kHz wide, so we can divide that neatly into XXX0000, XXX3000, XXX6000 Hz with only a little bit of waste.

More recently while I was operating on Field Day this year, I noticed a lot of people using XXXX500 Hz frequencies, and it occurred to me that if we consider the bandwidth as 2.4 or 2.5 kHz (as it apparently typically is as transmitted, even if receive filters aren't that sharp) then four channels fit into 10 kHz that way. Is that something people try do? (Reviewing my logs, some but not all of the 500 Hz frequencies fit this pattern.)

But trying to spot the pattern this way is an exercise in numerology. Are there any deliberately promoted, or somewhat accepted, schemes for SSB frequency selection?

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    $\begingroup$ +1 for question idea. I know that Maritime Mobile use 3 kHz channel raster, for example there's a list here. I think it's also the same for Aeronautical mobile service, but can't find a channel raster yet. $\endgroup$ – AndrejaKo Jul 1 '15 at 4:59
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I am not sure I understand the question but I will attempt to answer a part of what you are asking.

Thinking about this once, I said to myself: SSB is 3 kHz wide, so we can divide that neatly into XXX0000, XXX3000, XXX6000 Hz with only a little bit of waste.

No one does that. When you choose a particular frequency for SSB, you usually will look for empty space and that means probably at least 3 KHz distant from other signals. But, not always. As previously stated, if the band is crowded, such as during contests, this 3 KHz rule goes out the window. On modern radios today, many SSB operations will work with filters narrowing down their operating window to maybe 2 KHz. I sometimes have operated at 1.8 KHz since I have a 1.8 KHz roofing filter on my Elecraft K3. Yes, you can understand SSB at 1.8 KHz and it is not quality but who cares for SSB work especially in a contest.

Often I will arrange schedules with some buddies for late night 80 meter SSB chats. For some unusual reason, we have a habit of picking 3767 KHz or something like that. I like the odd numbers because it allows some kind of distance from a lot of regularly scheduled things that have a tendency to chew up the 1 KHz 0 digit (e.g. 3760, 3770, 3780,...). And, if not the 0 mark, they go for the 5 KHz intervals (e.g. 3760, 3765, 3770, 3775,...). So, regularly scheduled nets that can crowd the 80 meter band usually end up on the 0 and 5 1 KHz digit place so I avoid those for my schedules which are not regular.

And, when you make a schedule, you always inform the other party (parties) that if not found on such-and-such frequency, scan up 5 to 10 KHz and down 5 to 10 KHz looking.

But, no one that I know of has ever planned or thought of channelizing the bands into 3 KHz chunks. No one would obey that rule anyway so it is probably a waste of time.

On CW though or other digital modes, anything goes because the average signal width is much less than 1 KHz.

In my experience, on the 80 meter band, in the evening hours, no matter where you pick your frequency you are probably stepping on someones skirt or right on top of them. You raise QRL? to find if anyone is there but their answer may not be heard by you even though you may be heard by them so you may likely stomp on them anyway. This is especially true in the range 3900 to 3990 KHz.

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The answer to your question is no. There is not any internationally recognised standard of channelisation on the amatuer radio HF bands when operating SSB. There is a suggested band plan to keep different modes separated and give priority for specific usage but this is only a "gentleman's agreement".

The standard accepted "good conduct" is to ensure that your transmission is at least 3KHz away from any other that you can hear to avoid causing interference.

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There is no standard, but I note that many SSB stations transmit on an even kHz. I suppose this is just for tuning convenience for those who have accurately calibrated digital VFOs. It's very easy to scan the band with a 1 kHz step on many rigs. It means you don't have to fine tune if you're talking with someone who also has accurate frequency setting.

Using 1 kHz steps with ~2.4 kHz bandwidth means there aren't likely to be big gaps in spectrum usage. (Besides, plenty of people do not use 1 kHz "channels".) Sure you could pack people more efficiently with a finer step size, but when you consider variable propagation (the "hidden transmitter" problem), things work reasonably well.

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For normal, i.e. not contest operations, the convention is to try to be at least 3 kHz from the nearest station. During contests, however, that convention is regularly violated, and whatever interference such operation may cause is chalked up to there being a contest in progress. Contest operators learn to deal with such interference.

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    $\begingroup$ I'm afraid this doesn't answer my question. You're specifying a distance from existing signals; I'm asking about choosing (the last digits of) a frequency given the freedom to choose, i.e. you have an gap more than 3 kHz wide to work in. (I've now removed "spacing" from my question's title to avoid possible confusion.) $\endgroup$ – Kevin Reid AG6YO Jul 3 '15 at 0:09
  • $\begingroup$ The answer to the question, "Are there any deliberately promoted, or somewhat accepted, schemes for SSB frequency selection?" is "no." You answered your question in the first sentence, "I know that the amateur bands are not channelized." As far as it being inefficient, I'd say that it's as efficient as it needs to be. For one thing, I've never seen the bands so crowded that stations needed to be efficiently packed together--except during contests. For another, it's a dynamic system. Stations can always adjust their frequencies to maximize the number of QSOs on a band and minimize interference. $\endgroup$ – Dan KB6NU Jul 4 '15 at 1:09
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    $\begingroup$ I agree with the other answers and comments. That said, lots of people seem compelled to choose integer numbers of KHz for no good reason. I think it's a mild form of obsessive compulsive disorder. Someone on the qrz.com forums once said that he called CQ and someone came back and told him he was off frequency. :) Of course, this was pretty much a meaningless question before digital displays. $\endgroup$ – KT1F Jul 10 '15 at 17:30

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