On 6/24/06, Steve Baron - KB3MM <SteveBaron@starlinx.com> wrote:
>
> ----- Original Message -----
> From: "Martin, AA6E" <martin.ewing@gmail.com>
> To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
> Sent: Monday, April 25, 2005 00:18
> Subject: Re: [TenTec] cw creation
>
> > In theory, there really is no difference. The math is equivalent and
> > there's no way you can distinguish a CW signal that starts life as a
> > keyed AF tone and gets mixed up to RF and one that starts as "RF" or
> > some intermediate frequency oscillator.
>
> You mean the spectra of the output signals is identical, including sidebands
> ?
I'm not sure I understand your drift (no pun). The idea of "CW" is
that you have a keyed oscillator at some frequency, and that
oscillator may get translated (or even multiplied, in the old days) to
the TX output frequency. I'd say it doesn't matter if the osc
frequency is AF, IF, or whatever. The waveforms at the final TX will
be the same in a perfect system. This is just saying that translation
is translation; the carrier moves up or down, but the sidebands stay
the same. (100 Hz sidebands stay at 100 Hz relative to the translated
carrier, etc.)
There are provisos, of course.
The keyed oscillator frequency needs to be well above the keying rate.
The keying sideband widths should be a small fraction of keyed
"carrier" frequency. At least it's easier that way. Anything over
maybe 400 Hz should be OK unless you're a demon keyer. [Probably you
can use a lower carrier freq. if you key both I and Q versions
simultaneously ;-) ]
The mixing (translation) process needs to be clean. If you're using
an old rig with imperfect carrier and sideband suppression, you've got
troubles.
"Keying" an oscillator needs to be shaped, not just on-off, if you're
going to avoid clicks.
73, Martin AA6E
--
martin.ewing@gmail.com
http://blog.aa6e.net
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|