The “Getting on the Air” chapter is quite long and covers a bunch of topics. The first section, below, deals with tuning in a CW signal. By the way, I’m almost done with the book. It should be available soon….Dan
Tuning in
To make contacts, the first thing that you need to do is to learn how to tune your radio properly. When you tune in a signal, you want to make sure that you have tuned your radio to a frequency that is as close as possible to frequency on which the station you are receiving is transmitting. This process is often called “spotting” or “zero beating.” To do this, you tune your radio so that the tone you hear is as close to the frequency of the sidetone–the tone that your transceiver generates when you transmit–as possible.
While most experienced operators simply do this by ear, some radios have a SPOT function that you can use for this purpose. What this function does is to inject a continuous tone into the audio output of the radio while you are tuning it. When you’re right on frequency, the signal you’re trying to tune in, will nearly disappear. If you’re off frequency, you’ll continue to hear the characters being sent.
Some radios, such as the Elecraft K3, have an automatic zero beat feature. To use this feature on a K3, you simply press the CWT button, and the right half of the S Meter display becomes a zero-beat tuning meter. As you tune in the signal, you can see if you are getting closer to the signal’s frequency or farther away from it. Once you are close, you can tap the SPOT button, and the K3 will automatically zero beat the signal. How cool is that?
The method that I most often use with my older transceiver is to feed the audio of my radio into the laptop computer in my shack and view the signal with a program that produces an audio spectrograph, such as a PSK-31 program. I then simply tune the radio so that the audio frequency of the received signal matches the sidetone frequency. (I usually set my sidetone frequency to 600 Hz.) This is a very quick and easy way to zero beat a signal.
Sidetone frequency
In the previous section, I mentioned the sidetone frequency setting. This is the frequency of the audio tone that you will hear when your receive frequency matches the frequency of the station you are receiving. Personally, I prefer a 600 Hz tone, and usually set my sidetone frequency to this value. Some operators, though, prefer sidetones as low as 400 Hz and as high as 750 Hz. My suggestion is to play around with this setting and find the frequency at which a CW signal is most understandable.
Another thing to consider is that you may wish to vary the tone of the received signal during a QSO. This helps prevent fatigue, and can actually enhance the readability of the signal. Rather than actually change the sidetone setting, I do this by enabling Receiver Incremental Tuning (RIT) and then varying the RIT frequency to change the audio frequency of the received signal.
Filters
Another consideration when tuning in a CW signal is the choice of filters. In the past, radios would be equipped with fixed bandwidth filters, and for CW operation, 500 Hz was a popular choice. Some radios could be equipped with filters as narrow as 250 Hz.
Most modern radios use digital signal processing filters, and these filters can be set to almost any bandwidth. The reason for this is that the bandwidth is set in software and is not a hardware function at all. With this capability, you can set the bandwidth to exactly the value that you need for a particular contact. With the front panel controls, it is easy to set the bandwidth that you need.
I find that for most operating conditions, 700 Hz is the best setting for the receive bandwidth. Anything more and you hear stations 1 kHz above or below you. Anything less and the sound of the signal isn’t as pleasing to my ear.
That doesn’t mean that I never set the bandwith narrower than 700 Hz. When there is a nearby signal interfering with my contact, I’ll narrow the bandwidth as much as I need to to eliminate the interference. A similar situation occurs when operating a contest. In a contest, there are many stations operating in close proximity, and in that situation, using a narrow bandwidth filter may be necessary.
Some radios have a feature called passband tuning. With this feature, you can not only set the width of of the filter, but also the center frequency of the filter. This is a very useful feature in the event that there is an interfering signal just above or just below your frequency. For example, if the interfering signal is just about your frequency, then you can adjust the upper cutoff frequency so that it is below the interfering signal and filter it out.
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