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Author Topic: Use of Computer Generated CW  (Read 2972 times)
AA4PB
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Posts: 12854




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« Reply #15 on: January 28, 2008, 09:41:39 AM »

Mike, please explain to me what the output of a SSB transmitter with a single audio tone of 1000Hz injected into the transmit audio looks like on a spectrum analyzer. I've been in engineering for many years and looked at a lot of transmitter outputs. Every engineering book you read will tell you that the output of a SSB transmitter with a single tone input is a single RF frequency. It's CW - a steady carrier - there is nothing "modulated" about it. If the output is "modulated" then by definition there must be more than one RF signal output. If you key the tone on and off then the CW output keys on and off. For all practical purposes it is exactly the same a CW signal generated by any other means.

Of course there is a small amount of suppressed carrier and unwanted sideband but they are so far down from the main signal that for all practical means they do not exist beyond a very short distance.

If the output is MCW then please explain to me why modulating a SSB transmitter with mark and space tones is not AFSK (in lieu of FSK) and therefore illegal to use on the HF bands. Are you then saying that all of those using the digital sound card modes are operating illegally?
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W5RKL
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Posts: 891




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« Reply #16 on: January 28, 2008, 09:50:47 AM »


MCW is described in the FCC's part 97 rules and
regulations under section 97.3(46(c(4)) and
97.3(46(c(5)) titled "Definitions".

The list of authorized emissions and frequencies MCW
is permitted on are listed in part 97 rules and
regulations under  section 97.305(c) "Authorized
Emission Types".

Where section in the FCC's part 97 of the rules and
regulations does it say that audio generated tones,
whether it be from a computer sound card or any other
device, for PSK, RTTY, and SSTV, might be illegal? I
can't find it anywhere.

73
Mike
W5RKL
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W3LK
Member

Posts: 5639




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« Reply #17 on: January 28, 2008, 10:08:09 AM »

<< Thought I would get a simple yes or no answer. What I got is a definite maybe......or maybe not!!!! >>

It's still a good question. I'm interested in the FCC's response, because I think AA4PB is wrong on this and W5RKL and I are correct.

73,

Lon - W3LK
Naugatuck, Connecticut
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AA4PB
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Posts: 12854




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« Reply #18 on: January 28, 2008, 10:29:04 AM »

If you dig into the Part 97 it defines MCW as having an emmission designator beginning with the letter A, C, D, F, G, H, or R. SSB has a designator beginning with J which means one sideband, suppressed carrier. If you put a keyed tone into a SSB transmitter thats what you get out - one sideband and a suppressed carrier. The designator is therefore J and it doesn't fit the FCCs designation of MCW.

I still haven't had anyone here describe what comes out of a SSB transmitter when a single frequency tone is input to it. How is that output different than that of a CW transmitter? You are hung up on the term "modulation". Think about what the RF output of the transmitter looks like. If its a single RF frequency then its a CW signal regardless of how it was created.

Part 97.305 prohibits the use of MCW below the 6M band.
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AA4PB
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Posts: 12854




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« Reply #19 on: January 28, 2008, 10:53:32 AM »

Where section in the FCC's part 97 of the rules and
regulations does it say that audio generated tones,
whether it be from a computer sound card or any other
device, for PSK, RTTY, and SSTV, might be illegal?
-----------------------------------------------------
Part 97.305 note 8 is only authorized at 6M and above. Note 8 lists the designators where the digital tone is "modulated" onto a carrier. If the output contained a carrier and modulation (as in MCW or AFSK) then it would NOT be permitted below 6M. Since I am correct Smiley that injecting AFSK or keyed CW tones into a SSB transmitter does NOT result in an AFSK or MCW transmitter output the rules DO NOT prohibit creating the signals in this manner below 6M.

If you guys were correct in saying that the output of the SSB transmitter IS a modulated signal then the rules would indeed prohibit its use below 6M.
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N8UZE
Member

Posts: 1524




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« Reply #20 on: January 28, 2008, 10:54:55 AM »

Best thing to do would be to visit a ham that has a spectrum analyzer and the capability of generating CW the "normal" way by on/off keying and generating CW by injecting a tone into the radio when set on SSB.  These will look the same to the spectrum analyzer.  Either way, all that will show on the spectrum analyzer is a carrier that is being turned on and off.

Then look at an MCW signal.  It will not look the same.  You will see the carrier and two sidebands.

The FCC is concerned with how it looks on the output, not what you had to do to get there.
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W5RKL
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Posts: 891




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« Reply #21 on: January 28, 2008, 11:06:04 AM »

"Mike, please explain to me what the output of a SSB
transmitter with a single audio tone of 1000Hz
injected into the transmit audio looks like on a
spectrum analyzer"

A 1Khz tones injected into a sideband transmitter's
speech amplifier will display, on a spectrum analyzer,
a single RF signal containing a 1Khz sideband.

"If the output is "modulated" then by definition there
must be more than one RF signal output"

No, not true. There are varying audio frequencies
that's true, but only "one" RF frequency.

"If the output is MCW then please explain to me why
modulating a SSB transmitter with mark and space tones
is not AFSK (in lieu of FSK) and therefore illegal to
use on the HF bands."

Never said or indicated that AFSK, in lieu of FSK, is
not mark and space tones nor did I say it was illegal
on the HF bands.

"Are you then saying that all of those using the
digital sound card modes are operating illegally?"

No, never said that either.

73
Mike
W5RKL




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AA4PB
Member

Posts: 12854




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« Reply #22 on: January 28, 2008, 11:50:17 AM »

A 1Khz tones injected into a sideband transmitter's
speech amplifier will display, on a spectrum analyzer, a single RF signal containing a 1Khz sideband.
----------------------------------------------------
Exactly. And how is that signal any different than a CW signal? It's a pure RF sine wave that is a single signal offset from the suppressed carrier by 1KHz. Since the suppressed carrier isn't there then you can't tell the difference between the signal generated by a SSB transmitter and a signal generated by a pure CW transmitter. Therefore the output of that SSB transmitter is NOT modulated at all - its a CW signal plain and simple.

If I don't tell you, you don't have any idea how I generated that signal (with a CW transmitter or a SSB transmitter).

Again, you all are getting hung up on the term "modulation" rather than looking at the output of the transmitter.
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W5RKL
Member

Posts: 891




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« Reply #23 on: January 28, 2008, 02:19:51 PM »

Try answering the following 3 questions then apply
the answers to the issue of MCW in a single sideband
suppressed carrier transmitter.

1. How and where does modulation occur in a single
sideband suppressed carrier transmitter?

2. How or where is the "MCW" tone applied to the
single sideband suppressed carrier transmitter?

3. How is "normal" CW generated in a single sideband
suppressed carrier transmitter?



73
Mike
W5RKL
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W3LK
Member

Posts: 5639




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« Reply #24 on: January 28, 2008, 03:48:32 PM »

<< Again, you all are getting hung up on the term "modulation" rather than looking at the output of the transmitter. >>

The modulation IS the difference.

The output of the transmitter is NOT the same in both modes. In  true CW (interrupted carrier) all that is generated is a carrier being switched on and off with no audio modulation. The "tone" on the receiving end is generated by the receiver's BFO.

 In the case of MCW, an audio signal, with or without carrier, is being modulated by a tone generator and the result is a modulated audio signal, NOT an interrupted carrier.

While the net effect can be construed to be the same, the method of generating the CW is not. And the FCC says sending CW by modulating an audio signal is not allowed below 50 mHz.

73,

Lon - W3LK
Naugatuck, Connecticut
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KG6AF
Member

Posts: 357




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« Reply #25 on: January 28, 2008, 04:42:13 PM »

AA4PB and N8UZE are correct: there is no difference between a keyed-carrier transmission and the feeding of a (clean, of course) keyed tone into an SSB transmitter.  Provided the SSB transmitter is properly adjusted--i.e., the carrier's completely suppressed--there's absolutely no way the FCC could distinguish between two such signals by listening to them on the air, any more than they could tell what kind of PA transistor your rig is using.  The spectra are identical.

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AA4PB
Member

Posts: 12854




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« Reply #26 on: January 28, 2008, 06:56:13 PM »

The output of the transmitter is NOT the same in both modes.
-----------------------------------------------------
Lon, I don't want to sound mean, but you need to go back and look at some technical books on SSB. The output IS EXACTLY the same in both cases (a CW transmitter and a SSB transmitter fed with a single audio tone). When you feed a single tone into a SSB transmitter the output is a single (one and only one) frequency. Have you ever looked at the output? I have and I saw only one narrow frequency that looked exactly like any other unmodulated carrier.
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AA4PB
Member

Posts: 12854




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« Reply #27 on: January 28, 2008, 08:20:17 PM »

The Collins KWM-2 generated CW by applying an audio tone to the SSB transmitter audio input stage. The KWM-2 was used by hams and military world wide for many years.

Here's a quote from THE RADIO HANDBOOK by Bill Orr, W6SAI, page 5-1: "A single audio tone in a perfect ssb system remains a sine wave at all points in the system and cannot be distinguished from a cw signal generated by more conventional means".

And here's a quote from the FCC RULE BOOK, 11th edition: "It isn't MCW, however, unless a carrier is transmitted, as in the case of tone keying an FM or AM transmitter. If a keyed tone is transmitted over an SSB transmitter, there is no carrier, so the Morse transmission is CW, not MCW, and a BFO is needed in the receiver".
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N3OX
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Posts: 8847


WWW

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« Reply #28 on: January 28, 2008, 09:13:21 PM »

Given the crappy keying on some rigs, I bet you could do *better* on CW on some  using an audio tone with a well shaped rise and fall on SSB mode ;-)

Wonder what it would sound like to run error-function envelope  audio tone into the SSB...


http://fermi.la.asu.edu/w9cf/articles/click/index.html


may be able to set up a test with my rig using Matlab to generate tones... would be an interesting experiment some day if I could get a cleaner tighter CW spectrum using the sound card into the rig.

AA4PB is right on this one

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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W3LK
Member

Posts: 5639




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« Reply #29 on: January 29, 2008, 06:15:19 AM »

I yield. I was taught wrong all these years.

73,

Lon - W3LK
Naugatuck, Connecticut
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