Thanks for the research Martin.
I am a retired FAA type that worked at a long range radar (ARSR-1D) that fed
the Memphis Center (ARTCC). The method that the radar generated a signal
was kinda like CW. A magnetron was keyed with a pulse (dit) at about 363
pulses per second (high speed dits hi). Of course this keying was a very
high pulse of shaped negative voltage about 2 microseconds wide applied to a
magnetrons cathode. A pulse forming network shapped this pulse. During
this pulse, the magnetron a "cross field device" went into oscillation at a
frequency in the "L" band that was determined by its cavity. Now we have a
pulse consisting of RF energy. Again kinda like CW with rapd short dits.
Of course this was a "P" type of modulation not A type but still very
similar. And of course CW does have sidebands, determined by the rate and
shape of the dit/dah (duh).
I of course with my CW sending do not have to worry about generating a wide
bandwidth as my speed is slow enough to be safe!
73 to all, de wd4air
From: "Martin, AA6E" <martin.ewing@gmail.com>
Reply-To: "Martin, AA6E" <martin.ewing@gmail.com>,Discussion of Ten-Tec
Equipment <tentec@contesting.com>
To: Steve Baron - KB3MM <SteveBaron@starlinx.com>,Discussion of Ten-Tec
Equipment <tentec@contesting.com>
Subject: Re: [TenTec] cw creation
Date: Wed, 27 Apr 2005 11:39:43 -0400
On 6/26/06, Steve Baron - KB3MM <SteveBaron@starlinx.com> wrote:
> How does the FCC define CW?
>
Having nothing better to do, I went to the FCC website to read up on
Part 97 and what they say about CW. The relevant sections are 97.3
which refer back to 2.201 and 2.202. Some excerpts are at the end.
Classical amateur CW might be 100HA1A, specifying 100 Hz bandwidth,
or simply A1A. The ARRL FCC Rule Book has some useful material, too.
It seems that the FCC is interested in the signal that shows up on the
air and not how it is generated. Fair enough. Everything we have
been talking about in this forum is A1A, I believe. Some generation
methods (like tones into a poor SSB rig) are worse than others. FCC
requires signal purity to observe good engineering practices, or words
to that effect, and that may rule out the KWM-1 technique nowadays.
The DSP method (e.g., Orion = TenTec content!) can be as perfect as
you're willing to pay for.
As the Rule Book (8th ed.) explains, it would be possible to narrow
the "100 Hz" DSB spectrum of an A1A signal by eliminating one sideband
(50 Hz) and suppressing the carrier. (However you make it, CW does
have a carrier and sidebands just like a voice signal.*) I wonder if
anyone has ever done it, and whether a half-width carrier-less CW (or
psk31?) signal would be decodeable after HF propagation. You'd need
really tight frequency and passband control.
73, Martin AA6E
*A carrier? What about between characters? Yes, mathematically the
carrier is still there -- even after you turn your rig off. Of
course, there are also very low freq sidebands that conveniently
cancel out the voltage... So your rig had better be very very linear
or it won't be safe to shut off the power! Don't lose sleep over it.
;-)
================================
97.3(c)
(1) CW. International Morse code telegraphy emissions having
designators with A, C, H, J or R as the first symbol; 1 as the second
symbol; A or B as the third symbol; and emissions J2A and J2B.
2.201
(c) 1st symbol
(2) Emission in which the main carrier is amplitude-modulated
(including cases where sub-carriers are angle-modulated):..........
--Double-sideband................................................. A
--Single-sideband, full carrier................................... H
--Single-sideband, reduced or variable level carrier.............. R
--Single-sideband, suppressed carrier............................. J
...
--Vestigial sideband.............................................. C
...
(d) Second Symbol--nature of signal(s) modulating the main carrier:
...
(2) A single channel containing quantized or digital information 1
without the use of a modulating sub-carrier, excluding time-
division muliplex..................................................
(3) A single channel containing quantized or digital information 2
with the use of a modulating sub-carrier, excluding time-division
multiplex..........................................................
...
(e) Third Symbol--type of information to be transmitted:\2\
---------------------------------------------------------------------------
\2\ In this context the word ``information'' does not include
information of a constant, unvarying nature such as is provided by
standard frequency emissions, continuous wave and pulse radars, etc.
...
(2) Telegraphy--for aural reception................................ A
(3) Telegraphy--for automatic reception............................ B
(Also see 2.202 for the bandwidth designators which precede the
emission type designation.)
==========================================
--
martin.ewing@gmail.com
http://blog.aa6e.net
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|