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Author Topic: Questions about CW carrier oscillator injection side and CW side tone.  (Read 4694 times)
KK4EOF
Member

Posts: 11




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« on: December 17, 2011, 02:49:17 PM »

Hi, all.

New ham here, no radio or experience.  I'm saving money for a rig and meanwhile reading a lot.  The owner's manual for the Yeasu FT-897D has
a menu selection for "CW carrier oscillator injection side on CW mode".  The options are USB, LSB or AUTO.  My understanding is that CW is the
turning on and off of your carrier, which is not modulated otherwise.  This menu option seems to suggest that the carrier has an audio tone modulated
on it, and that it is transmitting in single sideband mode.  I am confused.  What's the story?

There is also a setting for the pitch of the CW side tone.  Now, I can see that the rig has to make some kind of sound if you are receiving an otherwise
unmodulated carrier, and that you can adjust the pitch of this sound to suit yourself.  That I can understand. The manual mentions a "CW spot"
feature.  "Because the side tone is a representation of the actual pitch of your transmitted signal, it may be used for zeroing in on another station."
The pitch of your transmitted signal?  Shouldn't your signal have no pitch?  How can the side tone be used to zero in on another station?  So very
confused.

Probably contained in answers to the above, but maybe not: what is zero beating another station?  It seems to be a method for adjusting your
transmit frequency exactly to the receive frequency of another station prior to sending a response.  How exactly is this done?
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AA4PB
Member

Posts: 12680




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« Reply #1 on: December 17, 2011, 04:19:02 PM »

What you are missing is that the receiver local oscillator must be set to a slightly different frequency than the transmitted CW signal. For example, if you want to hear a 800Hz tone then the receiver must be set to either 800Hz above or 800Hz below the transmit frequency. The CW USB/LSB selection determines whether you want the received signal to be above or below. Because filters are wider than the actual CW signal they let in other interfering signals. By changing the USB/LSB setting you can often eliminate some of the signals, depending on where they are located in relation to the desired signal.

The sidetone pitch frequency should match the offset that you want to use. If you want to receive signals as an 800Hz tone then you should also set your sidetone to 800Hz. That way (assuming the transceiver is aligned correctly) when you tune a signal so that its pitch matches your sidetone then you will be zero beat or transmitting exactly on the same frequency as the received station.
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K4KRW
Member

Posts: 98




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« Reply #2 on: December 20, 2011, 03:44:47 AM »

Zero beating is just ensuring that you are operating on the same frequency as the station you are receiving.  If you don't do this, the other station may not hear you when you reply.  For example, if the frequencies don't match and he has his filters set narrow your signal may get filtered out.

This is one of the things I like most about the FT-897D.  It is extremely easy to zero beat another station.  There is an LED on the front panel marked 'CW-T'.  Just tune the VFO knob until the LED blinks in time with the received signal.  That is it.  You are zero beat.  Works phenomenally well.

As mentioned by AA4PB, with most rigs if you are zero beat the frequency of the received CW tone matches the frequency of the sidetone when you transmit.  So, you should be able to listen to their signal and then key your transmitter and the two tones should be the same.  With some rigs, that is how you zero beat.  Believe me, that little flashing LED is a much easier and much more convenient way to to this.  I really don't understand why all manufacturers don't adopt this practice.

In fact, I liked the feature so much, I even found a way to add it to a QRP rig I have.

http://www.wb3aal.com/Pages/K6XX/K6XXCWIndicatorKit.htm
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