Found this referenced on the QRPL list, and thought it a good simple, wake
up call-reminder, and one which will cause me to make sure my side tone is
set as required. HTH, Wb4idu.
Zero beating, what is it, how do we do it and why should we do it
By N3EF
First, lets define what zero beating is in general. Zero beat is the
condition reached during a measurement or calibration when the beat
frequency between two input signals is no longer detectable. And the beat
frequency is the frequency produced when two signals are mixed or combined.
The beat frequency equals the difference or offset between the two
frequencies. In cw, we are using two audio frequencies to do this. One
frequency is your sidetone and the other is the pitch of the received cw
signal which changes as you adjust the tuning dial. In reality, we are not
listening for the beat frequency. We are listening for the sound of the two
signals going in and out of phase with each other as the two frequencies get
close to each other. The two frequencies are so close, you can barely tell
the difference between them, but you can hear a change in intensity as they
go in and out of phase with each other adding and subtracting in level. It
is a "wow...wow...wow.." sound that gets slower and slower as the two
signals get closer and closer in frequency. It is more pronounced if the two
signal levels are the same so you may need to adjust your volume and/or
sidetone level. It is easier to hear the "wow...wow" sound when listening to
two steady tones, but you can also detect it with one steady tone and one
switching on and off such as cw morse code. Once you get the hang of it, it
becomes second nature and you can do it very quickly. Here is the sound of
two steady tones of around 750hz that start out at 50 cycles apart and
gradually get closer until they are identical in frequency. The sound of the
two frequencies going in and out of phase with each other is very
distinctive. wowwow.mp3 And here is what it sounds like when receiving a
cw signal as I tune above and below his frequency. You can clearly hear the
distinctive sound made when the two frequencies are at or very near each
other. They start out with just the received cw and then you hear my
sidetone come on. zerobeat.mp3, zerobeat1.mp3, zerobeat2.mp3.
Now, some of the old timers will tell you that this isn't "real"
zero-beating. They will tell you that zero-beating is the way we use to do
it when we had separate transmitters and receivers. Well, they are wrong in
telling you that. The way they did it was just another way of getting your
transmit frequency the same as the one you are receiving and was also known
as zero-beating. The way we do it now is different, but it is still
zero-beating.
So why should we zero-beat anyway? Well, if we don't, then we are
transmitting on two different frequencies and using more bandwidth than
necessary. You may be QRM'ing another nearby station. The other op may not
like the pitch of the tones he hears and must use his RIT to change it. The
other op may be using a narrow filter and not even hear your reply. I
recently operated with a special event callsign during the Straight Key
Century Club's first anniversary special event. There were operators from
each call district using the same callsign appended with their respective
call district. I was calling CQ 1Kz away from another SKCC operator. People
answering just threw out their callsign without indicating who they were
responding to. This is normal and acceptable as a response but some of them
were 500Hz off frequency directly between us...so who were they responding
to? And what about the QRM they were causing because they didn't take the
time and effort to zero-beat. There was no big pile-up going on here as it
is an often used tactic to be heard when there IS a pile-up. I was amazed at
how many stations were calling me so far off frequency. Some people don't
know what zero-beating is, some do but don't know how to do it, and some
know how but think it is totally unecessary. You don't have to spend a lot
of time and be exactly on frequency, but you should try to get close. There
are many aspects of working CW that mark you as a good operator. I think
zero-beating is one of them.
There are other ways to zero-beat the other station. If your rig has a
cw-reverse mode, you can just switch back and forth from cw to cw-reverse
and adjust your dial until the tone sounds the same in each mode. You can
tune until you think your close and then turn on a narrow filter and tune
for max signal level. Some rigs like the Yaesu FT-897 have a zero-beat
indicator lamp. There are also zero-beat indicator kits that you can adapt
to your rig. If you have an audio output to your computer you can use one of
several programs available to do it via your soundcard.
One other thing you need to be aware of is that some rigs have an adjustable
sidetone pitch that does not track the rigs transmit offset. If you change
the sidetone pitch, you can't use it to zero-beat properly.
I hope this article and sound files have been of help and I hope you
consider zero-beating an important part of your operating practices.
Long live CW!
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