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Author Topic: How to correctly tune and transmit CW.  (Read 2132 times)

Posts: 11

« on: September 03, 2001, 11:05:19 PM »

I have been a ham for a year now. Most of my time has been spent on PSK. At first I did not have any interest in CW beyond passing the test, but now I am feeling the CW bug starting to tug at me. I have yet to make my first CW contact. How do I correctly tune a CW tone and use the RIT? I have heard of "zero beating" but how is it correctly done?

Posts: 20

« Reply #1 on: September 04, 2001, 04:34:09 PM »

hi Doug,

i got my technician ticket 10 years ago and, if all goes well, will pass my cw exam in December. The following is my understanding of the subject, if i'm wrong i sure hope someone will put us both right !

To start with the tuning:

You are able to hear a cw-station because of the "sidetone" your receiver creates. Suppose the station sends at 14.100,000 MHz. If your sidetone is (set at)600 Hz, the receiver actually listens at 14.100,600 Mhz. This offset is mixed with the keyed signal and produces the beep. Mind you: the vfo still points at 14.000,000 ! If you tune around it, the tone of the beep will go up or down, taking the vfo frequency along. This is ok if your just listening but if the tone is not equal to the sidetone, you'll be transmitting on a -slightly- different frequency than the other station is.

Pheeww, hope you can follow me there !


Let's say you've just finnished a cw-qso and i was listening in. I didn't get the beeptone in line with the sidetone's tone -with me so far ?- and i want to start a qso with you: down goes the key and, if your filters aren't set to narrow, you will hear either a higher or lower tone - or just a sort of "plunk"- than your sidetone. This is where your Receiver Incremental Tuning steps in ! You don't want to change your vfo setting because, because i would loose your signal i badly tuned to before. Instead you only change the Rx frequency a bit to get a proper signal from me.

We have a nice qso but what has happend ? We're taking up two frequencies maybe some 500 Hz apart! This is my fault ofcourse becuase i failed to properly tune in.


how do i tune in properly ?

My rig has a button marked "SPOT". Dunno what you have so i'll stick with mine.

SPOT simply send a tone to the phones or speaker at exactly the same tone as the sidetone. I now hear both rhe signalbeep and the sidetone. Remember they are both in the order of say, 600 Hz.

The beauty of it, you don't have to be an a-class musician to pinpoint a match of the tones: ever heard a big multiengined airoplane ? The WW2 films usually have some in them. The engines are revving at about the same number of revolutions and the sound has a slow change of pitch, usually a couple of times per second. The slower this pitch sounds, the better the match of rpm. Same goes for the spot and sidetone: Don't listen to the tones, listen to the slow pitch or "floating" as textbooks from my younger days call it.

Ok: you hear the North Korean station calling cq and you want to grab him first-time before the big-guns light up the sky ! He will hear you best if your spot on, so hit the spot button and listen to the float, slooowly turn your vfo. If the floating goes slower your in he right direction, if it increases turn the other way. Easy does it and you can turn it down to may once very second, maybe even longer. Presto, another qsl card to be framed ! The Korean operator also heard -maybe- a sortof "plonk" from Holland: he could have used his RIT to get a clearer signal, also using spot to zero the beat, but why bother ? The American with the spot-on sigs is easier to work !

hope this helps Doug,

73' Leo.

Posts: 73


« Reply #2 on: September 07, 2001, 08:49:55 AM »

Tuning a CW 'tone' is very subjective and very personal and the way you learn to do it should be suited to your own personal taste!! In my opinion, the first thing you should always do when tuning is to TURN OFF THE RIT! When I hear someone I want to talk with on CW, I turn on my CW filters (to say, 500Hz) and tune that signal for peak S-mtr reading, which puts that signal in the center of my filters pass-band. I then turn off the filters (unless there is close by QRM) and turn on the RIT. I then use the RIT to adjust the signal for a tone that is pleasant to MY ears. Just that simple! This allows you to (almost) zero beat your xmit frequency to the other stations xmit frequency (meaning he does not have to retune his rcvr or tune his RIT to be able to copy you.).

Generally the rcvr and xmtr are offset (by design), typically 700 cycles, from each others frequency by an amount that will produce a beat-frequency or a certain audio tone from your receiver. This fixed amount of offset is also the frequency center of the rcvr's filters passband. People with very sensitive ears (not mine!) can match the incoming signals audio frequency to the audio of your own xmitted audio tone. (I've been trying to do this for 50 yrs, and still can't do it!) If your ears allows you to be able to tell when you have the two tones matched, that is basically the same effect as a 'zero-beat'.

If your rig has a 'spot' button, such as Leo's has, what that does is shifts your rcvr freq to exactly your xmitter's freq. When you hold the 'spot' button, you then can tune the rcvr signal to 'zero-beat' or you are actually tuning your rig to the exact frequency of the station your going to talk with. When you do this, you will hear his tone get lower and lower in frequency, until you basically can not hear it any more, i.e., meaning the frequency difference, or the beat freq between your rig and his rig is at or is approaching a zero frequency difference.

Just remember, turn your RIT off and then tune your rcvr!!


Posts: 20

« Reply #3 on: September 07, 2001, 10:55:56 PM »

If your radio has a "spot" button that works by setting your receive frequency to zero-beat with the transmitter, I think you may have trouble using this to zero-beat. Why? Because the audio response of your radio's audio amplifier, speaker and/or headphones rolls off below around 100-200 Hz. How you are supposed to find a zero-beat that's 100 Hz below the lowest frequency you can hear in the radio is unclear to me. It would seem to me that using this method, you are very likely to have an error of up to 100 Hz or so. That is almost large enough to be a possible problem.

After all, if the other guy is using a 250 Hz filter, he can still easily hear signals up to 100 Hz on either side of his own (his filter response should be reasonably flat over that spread), but an error of 200 Hz would make him much less likely to hear you.

Leo's method, listening for a "beat" between the two tones, requires you to get within 5 Hz or so before you can even hear the "beat", then he goes on to get you within 1 or 2 Hz. All I can say is, WOW! I would never dream of trying to get that close.

Not only that, but if two stations are actually zero-beat, and if their keyer speeds are the same, it may be impossible for someone eavesdropping to tell when one of them stops and the other begins. This can actually be a disadvantage to a DX station working simplex - any confusion on the part of his listeners raises the chances of the pileup degenerating. For this reason, I believe it may actually be preferable to be just far enough off that other stations can tell the difference. A 20 Hz offset would seem to be sufficient for this.

So, I would advocate trying to get within, say, 50 Hz or so of the other guy, but then not bothering to try to get more exact, because it's hard work and I don't think it is worth the effort.

How close is 50 Hz? Well, the sidetone in my TS-850 (which is slaved to the transmit offset) is adjustable in 50 Hz steps from 400 Hz to 1000 Hz. For the musically inclined, the possible values are (close enough for government work, if not for a musician):
400 Hz: G above middle C
450 Hz: A
500 Hz: B
550 Hz: between C and C#
600 Hz: D
650 Hz: between Eb and E
700 Hz: F
750 Hz: F#
800 Hz: G
850 Hz: Ab
900 Hz: A
950 Hz: Bb
1000 Hz: B (almost two octaves above middle C)
At 400 Hz, a 50 Hz difference is a full tone. Even up at 1000 Hz, it's close to a semitone. If you have a musical ear, you'll easily be able to get the received tone within 50 Hz of your sidetone (and quite a bit closer if you use a low sidetone).

But what do you do if you have a tin ear? Don't despair, I have a solution for you. Connect the audio output of your radio to the line input connector on the sound card in your computer, start up a spectrum analyzer program, and away you go!

You say you don't have a spectrum analyzer program? Well, there's one built in to every sound-card digital mode program. There are lots of these available for free download. If you pick a program with a waterfall display that shows audio frequencies, you can use it to tune your CW signal. I like the waterfall displays in HamScope and MixW, because they are zoomable, so that the tick marks every 100 Hz are well-separated. Digipan, Zakanaka and WinWarbler also have tick marks every 100 Hz, but they are a bit closer together than I would like for this purpose.

Switch MixW or HamScope to CW mode, zoom the display in to a comfortable width, set the software's frequency marker to the frequency of your sidetone, and by adjusting your radio's tuning, you should have no trouble getting to within 50 Hz or better of zero beat. This should work even if you are tone-deaf. Practice with this for a while, and you may even get good enough at it to do away with the spectrum display and tune by ear alone.



Posts: 6

« Reply #4 on: September 08, 2001, 04:03:41 PM »

The PE1OBG explanation of zero beating a cw signal is the most eloquent and simple explanation that I have ever read. Have you considered writing a book?

Posts: 729


« Reply #5 on: September 16, 2001, 11:39:18 AM »

Most transceivers create a built-in off-set.  If you tune across a CW signal, it will be stronger on one side of zero beat than on the other.   If you tune to a comfortable pitch on the stronger side, something like, as already metnioned, 600 cycles, when you press the key to transmit, your transmitted carrier will be automatically shifted so that, even though your receiver is not dead zero beat with the fella you are receiving your transmitter will be nearly so.  In other words, you are not receiving on precisely the same carrier frequency as your transmitter is set to.   Unless you like extremely high or low pitches, if you tune to a "standard" pitch, on the stronger side of the received signal, you will be "close enough" when you transmit.  "Close enough" means well within his passband, even at 250 cycles bandwidth.  If you know the precise offset of your transceiver (and on many modern transceivers this offset is programmable, while on ones from the 60s and 70s it is not) you can learn that "pitch" in your ear and tune to that offset frequency.  That will put you "dead on," but if you even approximate that offset tone in your speaker, you are very close.   If you don't know the offset in your transceiver, you can guess it will be around 600 cps.  So if you tune the received signal to 600 cps audio tone, you are close enough.  It's really very easy to get very close to the precise frequency, but not as easy to get "dead on" from a technical aspect.  

In other words, don't make it harder than it is.  Tune to a comfortable tone for you, that is on the stronger side of the signal using your CW mode, and then transmit.  It's that simple, and need not be more complicated.  

If, though, you are using separate transmitter and receiver, the process of getting "dead on" or even "close enough," may vary quite a bit.  The only way to know is to find out how the specific equipment operates, and for that you need the manuals in order to determine offsets in the receiver's BFO and in the transmitters method of generating a CW signal.  There isn't enough room here to cover the different variations possible!

Bottom line: just enjoy it.  Forget about being technically, positively, absolutely "dead on" zero beat, and just practice tuning a received CW signal to the approximate tone of the offset in your transceiver.  You will, with just a dab of practice, be within 50-60 cycles of zero beat, almost all of the time, and it will become more comfortable the more you use it.  

Have fun.  We are amateurs. Enjoy that aspect of it.

Ed W5HTW  


Posts: 2

« Reply #6 on: September 18, 2001, 03:00:34 PM »

Try this URL:

it contains details of how to build a CW tuning indicator as per the FT1000D and some other up market rigs, essentially you adjust the offset to match the sidetone freq of your rig and then when you correctly tune in a station the LED will glow (assuming the sig is not too weak)
I hope that this helps
73  Tony G3ZRJ

Posts: 787

« Reply #7 on: September 21, 2001, 04:05:18 PM »

Assuming you have a modern rig, where the sidetone pitch matches the CW offset frequency, it ain't that hard. Just send a single dot while listening to the pitch your rig's sidetone makes, then tune the receiver until the CW station has about the same pitch. After you've tuned him in, send a second dot if you want to be sure. You don't have to be absolutely zero beat; his receiver's passband is going to be 250 Hz or more, especially if he is calling CQ.

In an operating session, I only have to send a dot before the first QSO, and only if I am answering a CQ and not calling CQ. After completing a QSO, I have listened to my rig's sidetone pitch for a long enough time that I can easily tune in the next station I want to call. Again, my signal may not be right on, but it will certainly be in his passband.

Tone deafness is real; I have a sister-in-law who cannot carry a tune. If you can't readily hear the relationship between the sidetone dot and the other station's signal (is it higher in pitch or lower), you will have to resort to some of the more elaborate methods described in this thread.

P.S. If you gotta send more than one dot, be sure the rig's power level is turned all the way down. Then you have to remember to turn it back up to make the QSO!

Posts: 31

« Reply #8 on: June 28, 2002, 02:00:30 PM »

  What's a RIT?

Posts: 8

« Reply #9 on: June 28, 2002, 03:38:13 PM »

Hi Bruce,

RIT stands for Receiver Incremental Tuning. It's usually a small knob on the
frontpanel of your rig which lets you adjust the Rx frequency without
changing your Tx frequency.

Suppose you have a qso with someone and you find his frequency drifting up a
bit. You could correct this with your VFO, but that would mean that not only
your Rx, but also your Tx frequency changes. If the other ham uses narrow
filters, he could lose you.

With the RIT control, you can track his frequency while staying put on your
Tx frequency. Careless use of RIT on both sides causes the qso to be held on
two different frequencies, it's allways better to tune in properly, saving

73' Leo.
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