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Can someone explain CW-USB, CW-LSB modes?

Discussion in 'General Technical Questions and Answers' started by N4NVD, Apr 9, 2018.

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  1. N4NVD

    N4NVD Ham Member QRZ Page

    I have just bought my first new rig in many years, a Yaesu FT-991A. I see that instead of simply having a CW mode, this radio has CW-USB and CW-LSB modes. This is confusing to me - can anyone explain to me why there's no longer a CW mode and why I should care about running CW-USB or CW-LSB?

    73 de N4NVD
    W6KCS likes this.
  2. N9XV

    N9XV Premium Subscriber QRZ Page

    C-U injects the BFO on the high side of the carrier & C-L injects the BFO on the low side of the carrier. Same function as CW & CW-R (CW REVERSE) where the BFO is injected on the "other side" of the carrier. Functionally, if you have QRM in either position you'll likely eliminate it by injecting the BFO on the "other side" of the carrier. Its actually a nice feature to have.
    AK5B, W4NNF, KC3RN and 4 others like this.
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    N9XV explained it nicely above, but here's another way to think about it:

    When you receive CW your transmitter and receiver aren't tuned to exactly the same center frequency, the transmit frequency and the receive center frequency are shifted a bit relative to one another as in 600-1000 Hz or so depending on the specific CW offset of your rig. In many rigs that CW offset is always shifted in one direction as in the transmitter being shifted up 750 Hz during transmit. Your rig allows the choice of whether that CW offset is to the high side or to the low side of the receiver center frequency which as posted above can sometimes be helpful in fighting QRM when there's another station close to your operating frequency.

    So think about these two situations assuming you have a 750 Hz CW offset:

    You're well zero beated and working a ham that's transmitting on 7.040 MHz. If your rig is in USB CW mode your receiver center frequency would be tuned to 750 Hz (the CW offset) below that frequency so that you'd be receiving the signal through your upper side band filters. IOW, your receiver center frequency would be 7.039250 MHz to hear the CW signal with a 750 Hz tone.

    But if you switch your rig to LSB CW mode you'd have to retune your receiver up to 7.040750 to listen to the station with that same 750 Hz tone but now through the lower side band receiver filters. In both cases you and the other ham would be transmitting on 7.040 MHz, the transmit frequency hasn't changed, all that's changed is the center frequency of your receiver that gives you the expected 750 Hz audio tone when the other ham transmits.

    The part that might not be immediately obvious is that it doesn't matter whether you and other hams use the same CW offset direction (USB vs LSB) and doesn't even matter if the specific CW offset is the same (e.g. 600 Hz, 750 Hz, 1000 Hz, etc.) as long as you both zero beat correctly you'll be transmitting on the same frequency and hear each other just fine even though your receive center frequencies would differ and depending on the rig the displayed frequency may differ as some rigs display transmit frequency in CW mode, others display receiver center frequency.
    AK5B, DB5DY, K8DQ and 4 others like this.
  4. K7GQ

    K7GQ Subscriber QRZ Page

    It would be well to remember which CW mode you're in when approaching a band edge ...
    AK5B, KS2G, KX4UL and 3 others like this.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    CW-U or CW-L is very important!

    If you're feeling low, use CW-L. If you're feeling high, use CW-U.

    Glad to help.:p
    PU2OZT, AB0XE and 9A5O like this.
  6. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    I thought it was the other way around to try and even things out! :confused:
    I stand corrected. :D
    AK5B and PU2OZT like this.
  7. K8AC

    K8AC XML Subscriber QRZ Page

    There's one other consideration: some people (me included) have a preference for how the CW note changes depending upon knob rotation. In other words, as I tune towards the low end of the CW band, I prefer the CW note to decrease in frequency with counterclockwise rotation of the tuning knob. On my rig, that is accomplished by using CW-L. For those who like it the other way, they can select CW-U and then the CW note will increase in frequency with counterclockwise tuning knob rotation.
    G6YYN and KX4UL like this.
  8. W0IS

    W0IS Ham Member QRZ Page

    It shouldn't make any difference, because in either case (at least on Yaesu), the frequency displayed is the carrier frequency. So if the VFO says 7001.0, you're OK either way.

    I normally don't pay attention. The only time you might want to switch is if you are working cross-mode with an SSB station. In that case, you'll need to use the same one they are using. (And you'll note that your VFO will read 600 Hz different from theirs, since their VFO displays their suppressed carrier frequency, and you are transmitting 600 Hz above that on USB, or 600 below on LSB.
    WD4IGX likes this.
  9. G3YRO

    G3YRO Ham Member QRZ Page

    To explain it another way, it just means that on Receive you can choose whether you listen in the same way as either LSB or USB, even though you are transmitting CW. (it doesn't affect your transmitted signal, or its frequency). So you are listening on one side of the carrier or the other, depending on which you select.

    On older rigs, the manufacturer simply chose for you . . . on some it was LSB, on others, USB.

    On some rigs, even when it doesn't give you the choice of whether you're listening to CW in LSB or USB mode, you can re-align the oscillators to your own personal preference.

    Being a mainly 160m operator, I'm used to tuning around in LSB mode . . . so I have set my rigs to do the same when on CW. As K8UC said, it's mainly about which way you prefer to hear the carrier change pitch as you rotate the dial !

    Even if you have narrow CW filters, you are still listening on that side of the carrier that you have chosen.

    Roger G3YRO
    AK5B, PU2OZT, K8DQ and 1 other person like this.
  10. KM3F

    KM3F Ham Member QRZ Page

    On my Kenwood TS2000 I can tune in SSB either side and chose the option to key CW without any other changes.
    It's in the menu.
    Or use the reverse button on the front panel when in CW mode.
    This is really not a new function.
    The trick is to understand the receive has to be offset or you would not hear the signal as a tone.
    The tone is the amount of difference between the radio oscillator and the received signal. ie 800 hz, 600 hz etc.
    And you can adjust the offset for the tone you most like to hear.
    On the 2000, more control is done with the DSP when in CW mode. Filter width and offset to help separate two signals close together.
    You can actually tune SSB in the CW mode by selecting the sideband to be tuned by using the CW reverse function. Some radio designs may or may not have this capability.
    Don't let that radio be smarter than you. Read the user manual as many times as needed, to get it.

    Good luck.
    Last edited: Apr 13, 2018

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