[Elecraft] AM with FM filter

[Joe Subich, W4TV]

 > Since modulation involves imposing one signal on a second signal to
 > obtain the wanted third signal, technically there is no modulation in
 > a K3.  The desired signal is directly formed digitally via algorithm
 > and placed without further processing into the linear TX string at the
 > 15 kHz IF via a DAC.

I don't know how Lyle does it but one "DSP Modulation" technique is
simply to convert the incoming audio to digital create a quadrature
version of the digital audio stream, multiply each of those streams
with either an in phase or quadrature version of the "carrier" and
combine (add) the resulting data streams.  In this case the "modulator"
is identical to a phasing SSB modulator only in the digital domain.

 > The K3 uses firmware directed direct signal generation.

It's still nothing more than doing mathematically what was previously
done in circuitry.

> It's comforting to call that voltage scalar pot plus an ADC the "RF"
> gain. But it's real hard to find the RF gain lead going to the CPU,
> cause the digital variable gain advice is time division multiplexed
> with a bunch of other stuff sent on a single lead to the CPU. It's
> "advice" because it has no direct affect on anything unless the
> firmware and CPU want it to, in very severe contrast to our daddies'
> analog radios.

Again, it's simply doing in mathematics what our fathers' radios did
in circuitry.  Simply because we can no longer point to a specific
diode and capacitor that converts a series of RF waves of varying
amplitudes into an audio frequency doesn't mean there isn't an envelope
detector (or an AGC detector depending on the size of the capacitor).

73,

    ... Joe, W4TV


On 11/7/2011 9:37 PM, Guy Olinger K2AV wrote:
> On Mon, Nov 7, 2011 at 8:23 PM, Joe Subich, W4TV<lists at subich.com>  wrote:
>
>> Since modulation is performed in DSP, there is no change in the TX
>> width.
>
> DSP modulation is an oxymoron of sorts.
>
> Since modulation involves imposing one signal on a second signal to
> obtain the wanted third signal, technically there is no modulation in
> a K3.  The desired signal is directly formed digitally via algorithm
> and placed without further processing into the linear TX string at the
> 15 kHz IF via a DAC.  And we don't normally refer to up-conversion to
> the TX frequency as "modulation."  So there is no modulation.  The K3
> uses firmware directed direct signal generation.
>
> We have SUCH a hard time walking away from our analog roots.  It's
> comforting to call that voltage scalar pot plus an ADC the "RF" gain.
> But it's real hard to find the RF gain lead going to the CPU, cause
> the digital variable gain advice is time division multiplexed with a
> bunch of other stuff sent on a single lead to the CPU.  It's "advice"
> because it has no direct affect on anything unless the firmware and
> CPU want it to, in very severe contrast to our daddies' analog radios.
>
> 73, Guy.
>