[Elecraft] K3 AFSK TX Filter

[Lyle Johnson]

In the case of the K3, the FSK mode uses DSP-generated IF frequencies in 
the 15 kHz range for the Tx, and simultaneously creates audio tones at 
the selected pitch-pair.

In AFSK mode, the radio requires that you supply audio to a Mic 
connector or the Line In connector.  The AFSK Tx filter may optionally 
be employed, but its use is not required and with later versions of DSP 
code is probably of marginal utility.

In the case of the KX3, the tones are generated at baseband.

73,

Lyle KK7P (who emphatically agrees these products are SDRs

> On 04/12/14 18:20, Joe Subich, W4TV wrote:
>
>> The K3 does not generate AFSK internally. AFSK is only transmitted
>> in response to external audio.
>
> But that is exactly how SDR architecture transmitters do generate FSK. 
> The only difference from what is popularly called AFSK is that the 
> tone starts as digital sine waves.
>
> The ones may be a bit higher pitch than one normally expects from 
> AFSK, but they are still audio tones.
>
> (As the K3 uses an I/Q structure, you could, theoretically, generate 
> the two tones as positive and negative tones at the same frequency, 
> but the problems with handling the DC crossover means that it is 
> unlikely that anyone would do that.)
>
> In case it is not clear, I consider both the K3 and KX3 to be SDR 
> designs.
>