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Author Topic: Zero Beat  (Read 1420 times)
SQUASH
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« on: January 10, 2006, 10:36:57 AM »

I will be taking my Tech exam in February, and will have HF privileges on the Novice frequencies having passed the Novice exam some 25 years ago, but having  let my Novice license lapse. When I get back on the air I would like to work CW, but have forgotten what it means to zero beat a frequency and how to go about doing so. I read the description in the licensing manual, but found it less then clear. Thanks.
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WB2WIK
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« Reply #1 on: January 10, 2006, 11:45:31 AM »

You don't have to zero beat anybody unless you're using a separate transmitter and receiver, with independant frequency control of each.

Nowadays, most everybody uses transceivers, and zero-beating is a thing of the past.

However, if you do have "separates" (different VFO control for receiver and transmitter), zero beating only describes a process used to "net" the transmitter onto the receiver's frequency.  One efficient way to do this is to tune the receiver so that the desired signal is "zero beat" (tuned into zero pitch, so the CW signal produces no tone at all from the receiver), and then adjust the transmitter's VFO for exactly the same.  After this is done, the two will be within just "cycles" (Hertz) of each other.

But that takes too long, and you can accomplish the same thing just by tuning in the desired station to a comfortable pitch and adjusting the transmitter VFO to produce that same pitch (approximately, by ear) in your headphones.  That'll get you very close, and close enough 99% of the time.

You don't need to "zero beat" a transceiver, but if you tune most transceivers so the pitch heard in your headphones is the same pitch as that of the CW sidetone produced by the transceiver when you close your own key, you'll be "zero beat" (on the same frequency) with the station you tuned in.  That is to say, the transmitter frequency will be set to the receiver frequency as long as you tune in a station to be the same pitch as the transceiver's sidetone.  Once you get used to this, it takes zero effort or additional time.

WB2WIK/6
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KB9X
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« Reply #2 on: January 10, 2006, 03:25:24 PM »

What WB2WIK says is true, but I have noticed that many people aren't very good at matching the pitch of the sidetone to get on frequency.  One of the advantages of CW is the fact that it requires so little bandwidth -- you can pack a lot of QSOs into a small segment of the band.  But you can only do this if the pairs of stations are on the same frequency.  If you can't match the other station's frequency, you're using more bandwidth than you should, and you might be QRMing a nearby QSO unnecessarily.

Being able to exactly match the frequency of the other station becomes critical when you're working DX, contesting, or doing serious traffic work.  In these cases, it's likely that the other station will be using a narrow filter and won't hear you at all if you're not right on frequency.

That said, most tranceivers have some method of turning on the sidetone (but not keying the transmitter).  This can be used to provide an actual tone to match with the pitch of the incoming station.  With a little practice, you can even hear a zero beat between the tone of the received signal and the sidetone as you tune the receiver.  This puts you right on frequency.

If you're really lucky, the rig might have a zero-beat button that, when you press it, adjusts the sidetone so that you literally tune for a zero beat.  This makes it even easier.
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SQUASH
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« Reply #3 on: January 10, 2006, 03:51:17 PM »

Thank you. That was very helpful. I do have a kenwood transceiver.
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N3EF
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« Reply #4 on: January 10, 2006, 03:57:15 PM »

  Zero beat is The condition reached during a measurement when the beat frequency, the frequency produced when two signals are mixed or combined, between two input signals is no longer detectable. This should be done every time you tune in a cw signal, even on modern transceivers, for two reasons. One reason is so that you are using the minimum necessary bandwidth. You zero beat so that your both transmitting on the same frequency. The second reason is so that when you reply to the cq, the other station will hear his "prefered" cw tone. If I like a 700Hz "tone" and have my offset at 700Hz, if the other station zero beats me, then I'll hear him at 700Hz. If he doesn't, then it will be some other tone and I'll have to use my RIT to get it to my prefered tone. There are different ways to zero beat. If your rig has a "spotting switch", when you press it, you'll get a steady tone of whatever you have set for your offset. Then while holding in the switch, you tune his signal and as the two frequencies get closer together you'll hear another "pulsing" sound that becomes "slower and slower" as you reach zero beat at which time the "other" sound disappears. You don't have to be exact here, just close. One of the nice features of my FT-897, modern transceiver, is that it has a zero-beat led indicator so you can zero-beat very quickly. You can even build your own tuning aid if you find it difficult to do it by ear, but once you figure it out, it becomes easier each time. But again, the method you use depends on the rig. In some rigs such as the Kenwood TS-50, the cw offset does not track the sidetone pitch setting so consult your op manual.
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N1BBR
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« Reply #5 on: January 11, 2006, 05:49:50 AM »

A cool topic.   I really enjoy hearing 2 ops line-up together.  Its a real treat.  Years ago I operated a Ten-Tec that had a built in side-tone w/ momentary button which allowed line-up to other station on recieve.  So, pretty much every active cw audio filter I have ever had, I built this feature into it.  Today I am using a passive design. I like this, as it does not introduce any of its own noise. My prefered center freq is 770hz. I built in a 3 level bandwidth switch and on the most narrow setting there is such a noticable peak as I tune toward a station, that it has taken the place of the built in osc.  I also put in a switch for shifing center freq up/down.
The reall challenge is getting a call from someone who is WAAAAAAAAAAAAAAAAAY off!  In this case, RIT does the duty ;~>
HAVE FUN!!
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SQUASH
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« Reply #6 on: January 11, 2006, 08:14:12 AM »

Thank you.I now understand the reason to zero beat. But, you wrote one thing that is not clear to me. You wrote that you like a 700Hz tone and have your "offset" at 700hz.I don't know what you mean by "offset." Can you clarify for me?
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WB2WIK
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« Reply #7 on: January 11, 2006, 08:26:38 AM »

Offset is the difference between the frequency displayed on the dial or digital readout and the actual carrier frequency, for a CW signal.  Most transceivers have a "default" offset in the 500 Hz to 800 Hz region.  Probably the most popular are 600 or 700 Hz, because this is a pleasing pitch for most people.  But in most transceivers, you can change it to something else, if you wish.

The "zero beating" aspect discussed for transceivers is interesting, but I don't know any serious CW operators who bother.  I certainly don't.  If I turn off my VOX (which works the QSK) and push the keyer paddle, I hear my sidetone in my earphones without transmitting a signal.  I do that, sending continuous dits or dahs, while tuning the receiver across the desired signal, until the tones exactly match.  

Anybody who doesn't have a "tin ear" (that is, anyone who isn't tone deaf) can do this in about a second and land within a couple of Hertz.  That is absolutely, positively close enough.  To attempt to be "exactly zero beat" with another station unless you're in a frequency measuring contest is silly.  Nobody cares, and being a few Hz off surely doesn't occupy excessive bandwidth or put your signal outside of anyone's passband.

I guess it might take practice, though.  I've been doing it for so many years I don't think about it.

Ironically, since some rigs drift, unless you're willing to continuously re-zero another station, it's very possible that two stations will begin a QSO dead on each other and by the end of the QSO be 100 Hz or more apart.  Part of life, and still not band hogging.  I like working guys using old Boat Anchors, and there are a lot of them on the bands -- most of them will drift unless they're using crystal control.

WB2WIK/6
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N3EF
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« Reply #8 on: January 11, 2006, 08:59:57 AM »

WB2WIK Wrote:
"If I turn off my VOX (which works the QSK) and push the keyer paddle, I hear my sidetone in my earphones without transmitting a signal. I do that, sending continuous dits or dahs, while tuning the receiver across the desired signal, until the tones exactly match."

  That IS zero beating unless your just hearing the two tones and not the beat note but as the two tones get close in frequency, the beat note will jump out at you. And as you say, you should NOT be transmitting when doing this. Your rig will show your transmit frequency. Your receive frequency will be the difference between the transmit freq and your offset. If they were the same and the other station zero beat you, then you would hear nothing. But as I said before, make sure that if you change your rigs default sidetone pitch, that the offset tracks it. Otherwise, zero beating to get on his transmit freq will not work. SQUASH, which model rig do you use?
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SQUASH
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« Reply #9 on: January 11, 2006, 01:02:04 PM »

Thanks guys, I got it now. Thanks very much for all of your assistance on this. I have a Kenwwod TS440-s, which will allow me to turn off my VOX,key without sending out a signal, and hear my sidetone in my headphones. I will be taking the exam next month and will then put this learning to the test.
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W5HTW
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« Reply #10 on: January 11, 2006, 02:32:41 PM »

Good luck with the test.  I visit 40 CW Novice band fairly frequently, so perhaps I'll find you there one of these days soon.

If you call CQ, and I answer you, and you hear me, we have done well enough.  There are all kinds of ways to be sure we are within 10 cycles of each other, but if, without involving the RIT, we hear each other, we are doing the job.  

I do, though, use separate transmitter and receiver most of the time.  But don't worry about it.  If I call you, I'll be on your frequency.  If you call me, and I hear you, then I will still be on your frequency.  So unless you are looking for a technical explanation of zero beat, just get on the air and have fun (when you get the ticket.)  If you are using a 500 Hertz filter, and you hear the other guy, you are going to be heard.

Again, good luck.
ed
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SQUASH
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« Reply #11 on: January 12, 2006, 03:34:49 PM »

Thanks, Ed. Once I have my license I will keep a look out for your call on 40 meters.

Ron
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N7DM
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« Reply #12 on: January 12, 2006, 05:05:46 PM »

I don't know that my info will do you any good, BUT... I run Ten-Tec and, frankly, that raspy 'side tone' is so annoying that for Non-Contest work, *I* use a monitor receiver... It happens to be an ICOM R-70, but the point is, I hear a nice, clean signal from my Corsair. I hear what The Other Guy hears.  And since the R-70 listens to BOTH signals, I usually, truly... Zero Beat the other signal. Useless effort, but I do it.  Those that have been around long enough will remember early XCVRs with no RIT/Offset.. and The Chase two CW ops would do with each other as they constantly tuned for their ear...which changed their XMIT freq...  HI HI
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KC9HVN
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« Reply #13 on: January 24, 2006, 02:58:10 PM »

Think of it this way, in a direct conversion reciever (one that has no filters or BFO) detection of the carrier is carried out by mixing the vfo freq with the incoming carrier freq, if the frequencies match, i.e. incoming = 7.0 mhz, vfo = 7.0 mhz the result is two products, one at 0mhz and one at 14mhz, if the vfo is moved up or down a few hundred hertz, you will "hear" the carrier (or more accuratley the product of the offset) on either side of the carrier freq, the silence in the middle is the "zero beat". If you use this same vfo to drive a transmitter, your transmitted frequency will be off by whatever offset sounds right. I.e. in a qso with me, you'd "hear" me at 7.0mhz + - 800hz, and if you replied at 7.0mhz +800hz I would not hear you (I usually use narrow filters Hi!).

73's
Mark.
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N5EAT
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« Reply #14 on: February 03, 2006, 06:19:45 AM »

I find it very useful to zero beat a cw signal on rigs which don't have some kind of illuminated indicator to tell you that you're "on" frequency - like the little blue light on my ft-857 that flashes with the sound of the code when you're right where you should be.  If you're right where you should be and you invoke your really narrow cw filter, you'll still hear your signal.
If you have a tin ear as I do, you punch the filter button and lose your station.  I started zero beating about 15 years ago when a guy told me I was way off frequency.  Just turn your tuning dial in a manner that the signal goes down in frequency until it "disappears".  Then tune up 700 HZ.  At this point, you'll be right on.
For some reason, I like to listen to a signal at a really high pitch.  If I don't zero beat, and the other op has his filter on, he may never hear me calling him.
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