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Author Topic: CW... Noob qestion.  (Read 2774 times)
N6SBN
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« on: January 05, 2013, 12:19:06 AM »

Kenwood TS-590

When listening to 20  meter USB, I can hear CW.   I switch modes to CW and (being on the same frequency), I can't hear the CW...  Sometimes, it's just the oposite, I can hear the CW on the CW mode, but not on the USB mode. (?)           Is CW done on USB or the CW mode or both?  I suspect this is pretty basic, but I don't understand it.

Thanks in advance...
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M0LEP
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« Reply #1 on: January 05, 2013, 12:39:40 AM »

Check what frequency offset your sidetone oscillator is using, and whether it's set higher or lower.  When you hear CW with the rig in USB but can't hear it when you flip to CW, tune up and down a bit 'til you find the CW signal again...

You'll hear CW when in USB mode if the CW tone is within the SSB passband, and the tone frequency will be the offset between the (suppressed) SSB carrier frequency and the CW frequency.
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AA4PB
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« Reply #2 on: January 05, 2013, 06:56:31 AM »

You can copy both SSB and CW stations (AM stations too) in SSB mode. In fact, you can receive SSB stations in CW mode, although it usually doesn't sound too good due to the often narrower filter bandwidth. As stated in the previous post, the receiver frequency shifts when changing between SSB and CW modes so you may have to tune around a bit to get the signal into your receiver IF filter passband.

Essentially, selecting a mode on the receiver doesn't somehow "block" all other modes from entering the receiver. Any signal will pass through the receiver if it is tuned so that some part of the signal falls inside the IF filter passband.
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N6SBN
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« Reply #3 on: January 05, 2013, 07:20:06 AM »

  So, the issue is the accuracy of the receiver between modes.
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AA4PB
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« Reply #4 on: January 05, 2013, 07:52:54 AM »

It's not a matter of "accuracy". It is that by design, the receiver frequency must shift in order to put the desired signal in the IF filter passband. The result is that you often have to retune the VFO knob in order relocate the signal when you change between SSB and CW modes.

On SSB the dial displays the suppressed carrier frequency. On USB the received signal occupies from that frequency to about 3KHz higher. On LSB the received signal occupies from that frequency to about 3KHz lower.

On CW the dial displays the frequency of the properly tuned CW signal. The actual VFO frequency is offset by about 600Hz so that you get a 600Hz beat note that you can hear. That offset and beat note is often different on different receivers and adjustable on some but it is always in the low audio range so you can easily hear it.

So, I wouldn't call it "accuracy" because its VFO offset by design.
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N6SBN
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« Reply #5 on: January 05, 2013, 02:17:31 PM »

  Okay...  Perfect explanation.  Thanks so much....
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WB2WIK
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« Reply #6 on: January 08, 2013, 01:57:48 PM »

It's not a matter of "accuracy". It is that by design, the receiver frequency must shift in order to put the desired signal in the IF filter passband. The result is that you often have to retune the VFO knob in order relocate the signal when you change between SSB and CW modes.

On SSB the dial displays the suppressed carrier frequency. On USB the received signal occupies from that frequency to about 3KHz higher. On LSB the received signal occupies from that frequency to about 3KHz lower.

On CW the dial displays the frequency of the properly tuned CW signal. The actual VFO frequency is offset by about 600Hz so that you get a 600Hz beat note that you can hear. That offset and beat note is often different on different receivers and adjustable on some but it is always in the low audio range so you can easily hear it.

So, I wouldn't call it "accuracy" because its VFO offset by design.


I agree, but the offset isn't always 600 Hz.  Different manufacturers settled on different fixed offsets for many years, but most of the modern DSP transceivers allow you to select the offset (pitch) to anything you wish.  ~500 Hz to 1000 Hz has been used by those not giving you the option.
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AA4PB
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« Reply #7 on: January 08, 2013, 02:40:43 PM »

Yes, "about 600Hz" means 500 to 1000 Hz  Grin
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M0LEP
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« Reply #8 on: January 11, 2013, 09:52:59 PM »

Yes, "about 600Hz" means 500 to 1000 Hz  Grin
I've heard an old-timer say he sometimes uses an offset as low as 300Hz in some conditions, because he can pick the lower notes out more easily...
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PA0BLAH
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« Reply #9 on: January 12, 2013, 09:43:59 AM »

I've heard an old-timer say he sometimes uses an offset as low as 300Hz in some conditions, because he can pick the lower notes out more easily...

I can confirm that. Turn the qrm station zero beat. And the bandwidth of the brain filter is about one octave.
« Last Edit: January 12, 2013, 09:54:59 AM by PA0BLAH » Logged
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