Why avoid frequencies ending with .0 kHz?

A rough survey, which could certainly be conducted with greater quality, shows that an estimated 80% or more amateur radio CW operators use frequencies that end in a round .0kHz. There are a few reasons for this, the most notable are that with the era of digital displays it looks a lot nicer to e.g. have 21023.000 on the dial than some random number.

We can thus say that the main overall reason is psychology: the human minds often like order, and such numbers give a clean impression on the brain, and don’t raise anxiety. However, in the olden days there was much less precision both in frequency readouts and in stability of CW signals which often had a drift in addition to a lovely chirp or a less lovely buzz.

So, why do we advise against using frequencies ending with a round .0 kHz? There are many good reasons to avoid frequencies ending with .0 kHz whenever possible.

Before we lay them out, perhaps have a think as to why there might be disadvantages in using amateur radio CW frequencies which end on a round .0kHz and make a list, mentally or on paper. This exercise helps us to think a little outside the box on operating techniques, and you can use your notes to leave comments on any points that we may have missed.

Ready? Here goes!

First reason is QRM. A CW signal is very narrow and these days extremely narrow and stable. On top of this, many rigs have been calibrated to within a few Hertz in accuracy of transmit frequency compared to the digitally displayed frequency. Let us explore this aspect of the problem further.

You pick a clear area of the band, and adjust your display to read a nice .000 kHz and after checking if the frequency is in use you proceed to call CQ. However, on most HF bands you are going to have a dead skip zone, in addition, your local noise level and antenna performance are going to limit what you hear. Try listening on various remote SDR and you’ll see what we mean.

You are rather unlikely to be the only person calling CQ on that particular frequency. Let’s say, your noise level is low, you have a great vertical antenna, and you are in England and on 20m during the afternoon. At the same time, a station in Japan and another in Panama are using the exact same frequency, no problem, none of you can hear each other.

Then, a station in Russia wants to reply to you but he is also hearing the Japanese station clearly. You are both zero bearing with each other with your CQ calls and so he looks elsewhere.

Meanwhile, a station in California replies to the Panama station, his noise level preventing him hearing the Japanese who is running 200W, while he is running 1kW into a vertical and hearing the Mexican well above his noise level. The Japanese, who was just replied to by a station in Australia, now has QRM from California and cannot hear the Australian during his first over.

During this short time period, a station in Holland, who cannot hear the British station, starts calling CQ, and also a QRO station in Singapore suffering a high local noise level, who is replied to from Indonesia.

This kind of situation is actually very common, especially on the popular areas in the 20s from band edge.

However, a shift of 100Hz or more is usually sufficient for distinguishing signals, depending on signal strength, the ear and brain is a good filter.

This is one of the main reasons why it is a good technique to reply to a CQ caller on a .0kHz by changing your TX frequency to .9 just below or .1 just above. The caller is surely not using a 100Hz filter during a CQ call, they certainly should not be. So they’ll hear you reply, with the benefit that if one of you has QRM zero beat on the frequency, the other won’t and so can be advised to QSY a little.

Those with less than 1kW and a beam would benefit even more from avoidance of .0 kHz frequencies by at least 200Hz , as no amount of CW QRM other than local noise levels and propagation limitations, is likely to affect you if you do so.

There are other reasons to avoid frequencies ending with .0 kHz, including that most of the dreaded 5NN TU low quality high quantity activities take place on such frequencies, while more of the QRP and high quality QSO take place on frequencies 200 Hz or more off a .0 kHz.

You can still get the psychological satisfaction by rounding your display to .200 or .250 or .500 if you wish, still greatly increasing your chances of not being zero beat with anyone anywhere.

In fact, while we have been wondering where those of us who decry the unhealthy low quality fast food of 5NN TU should go to hang out and find others wanting a good QSO, instead of a particular part of the band (Friendship TOP5 for example) we can, or in addition, make sure we’re not within 200 Hz of a point zero and increase our chances of having a good QRM-less real QSO.

Are there any disadvantages in not using a round kHz frequency? I can think of only one: some few rigs and operators may have settings with a narrow filter and tune the band in 1 kHz steps, or 0.5 kHz steps. This can be the case with a QCX mini rig for example. But this is not a frequent issue, and tuning in 500 Hz steps may still pick up signals in between.

So, next time you call CQ, do band occupancy a favour and also increase your chances of getting a QRM free QSO: move at least 200Hz off any round kHz sticking to between .2 and .8 kHz, and, reply to a CQ caller by shifting .1 above or below.

Contesters know this situation well, and you’ll find very random band occupancy during contests.