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Author Topic: On Using CW-R (reverse)  (Read 3603 times)
K7PEH
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Posts: 1124




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« on: March 14, 2009, 08:03:20 PM »

I am trying to figure out why I want to use CW-R (on my Pro III).  Now, I did a search on the CW forum here for CW-R (Reverse) and read the posts.  I am still not sure what it is all about.

My Pro III manual merely describes how to use it, not why I want to use it.  I have read where you can use CW-R for zero-beating a signal, OK that is fine, but was it invented for that.

I suppose the biggest mystery is that I am not even sure what it does.  I tried a google search but unfortunately there are a lot of hits of other junk when you type in CW-R or "CW-R"

So, part of what I have discovered is that this seems to have something to do with "lower sideband".  When I hear "lower sideband" I think of SSB, not CW.  Isn't CW merely on-off keying on the designated frequency.  Sure, side-bands are generated due to the on-off keying, but this is just the physics of the matter, not a design choice such as SSB (LSB, USB), right?

My CW experience I admit is rather limited.  I was a novice back in the 1960s and none of this CW-R stuff existed back then (as far as I can remember).  And, so far, with 2 years of CW back under my belt, I haven't found a reason to use CW-R.  But, I have lots of questions, maybe I want to use it.  I have no idea.
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KC2MJT
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Posts: 59




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« Reply #1 on: March 14, 2009, 08:08:45 PM »

This site may clear this up for u. In short CW-r (reverse) is a way to shift your passband to avoid QRM.

http://kb6nu.com/cw-bass-ackwards/
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K0RS
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Posts: 788




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« Reply #2 on: March 14, 2009, 08:13:09 PM »

A CW signal has both an upper and lower sideband on either side of zero beat.  CW reverse simply lets listen to opposite sideband from the receiver's "normal" CW passband.  If there's an interfering signal on the one sideband of the station you're trying to receive, the CW-R function lets you switch to the opposite sideband which may well be in the clear of the interfering QRM.
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VK3GDM
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Posts: 28




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« Reply #3 on: March 15, 2009, 05:13:38 AM »

The CW reverse mode changes the BFO frequency from upper side to lower side injection, or visa-versa depending on the rig design.  

This allows you to change the tone frequency of an interfering signal that is just off frequency from the wanted signal.

If you are zero beat with the wanted signal and change to CW-R mode the wanted signals audio pitch will not change.

I find it very useful in eliminating high pitched interfering signals.

Here is an example:
I am zero beat with a wanted CW signal on 7010 kHz.
I have my CW pitch set to 600Hz and in normal CW mode my BFO frequency is on the low side of the carrier. Therefore my BF0 freq is 600Hz lower than the IF in order to produce the required 600Hz tone.

An interfering signal arrives 400Hz higher than my wanted signal, thus producing an annoying 1000Hz tone in my speaker.

I quickly hit the CW-R button and my BFO frequency shifts up 1200Hz, putting it 600Hz above the wanted signal and only 200Hz above the unwanted carrier.
My wanted signal still appears at the speaker as before at 600Hz.
The unwanted signal audio frequency has been shifted into the sub-audible area and affectively eliminated.

I use this feature of my little ic718 often. I don't use very narrow filters though and I guess it would be less affective if you use narrow filters.  But even just shifting the interfering signals pitch a little can help your CW brain lock onto the one you want.

73
David




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W4YA
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Posts: 317




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« Reply #4 on: March 17, 2009, 07:21:56 PM »

I always try to use CW and CW-R on my 746PRO to zero beat as described by VK3GDM.
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W9OY
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« Reply #5 on: March 18, 2009, 07:36:51 AM »

CW does not have sidebands.  It is not modulated (at least it shouldn't be).  

You have to offset your receiver's frequency from the carrier's actual frequency or what you would hear is a zero beat signal.  If you offset you can offset either to the upper side or to the lower side.  So what you are choosing when you choose CW-U or CW-L is which side you offset your receiver so you can get a tone instead of being zero beat.  Some radios follow the convention of 40M and below is L and 30M and above is U.  Personally I prefer all L, since the radio tunes the same way no matter what band I am on.  

73  W9OY
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K7PEH
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Posts: 1124




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« Reply #6 on: March 18, 2009, 07:49:49 AM »

W9OY says "CW does not have sidebands.  It is not modulated (at least it shouldn't be)."


Actually, I think your description is correct in how the upper and lower side of the "center" frequency is used by the BFO for generating the audio tone.  But, your statement I quote above is not really correct.

CW that is truely continuous, that is key-down, does not have sidebands as you say, or very nearly zero side bands.  But, on-off keying is indeed a modulation of the signal.  And, this modulation creates sidebands.  Now, these generated sidebands though are not pertinent to this discussion of CW-R.  CW-R works in the same way, as you describe, whether the sidebands are there or not.  

In think that there is confusion though in how the term "sideband" is used.  The more usual interpretation, as in LSB and USB, is the focus of the signal represented by energy carried by that sideband.  But, in this discussion, my focus and I think the focus of others, is that the sideband is merely the upper and lower portion of the frequency spectrum in the close neighborhood of the center frequency.
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