[Elecraft] K3 - Filter suggestions for new builder

[Joe Subich, W4TV]

The limit occurs several places ... adjust the "HI" setting and one
will find 4.20 is the maximum available.  There is also an analog
lowpass filter in the audio (headphone and speaker) between the DAC
and the headphone/speaker amplifiers.

I'm sure this limitation derives from the roughly 10 KHz clock/sample
rate used for the DAC ... Nyquist says the maximum frequency can not
be more than half the sample (clock) rate.  4.2 KHz is plenty good
enough for communications audio ... and not bad for AM with fading,
noise, and interference typical of medium and high frequencies.

The FM filter still provides noticeably better double sideband AM
response (4.2 - 4.5 KHz with DSP/LPF skirts) than the AM filter
(3.0-3.3 KHz depending on the IF filter response).

73,

    ... Joe, W4TV


On 9/26/2012 7:23 PM, Don Wilhelm wrote:
> Sorry, but yes, the K3 audio is limited at 4 kHz, no matter whether it
> is to the headphones or to the speaker.  Please do not "shoot the
> messenger". but that information is in the archives of this reflector in
> several places - it has been discussed periodically.
>
> If you want to lobby for extended audio response, that is fine, but I am
> just saying what the limits are today.  Whether those can be extended or
> not is for the DSP designer to answer.
>
> 73,
> Don W3FPR
>
> On 9/26/2012 7:11 PM, Dale Boresz wrote:
>> On 9/26/2012 1:35 PM, Edward R Cole wrote:
>>> ...  But I learned that audio is limited to 4-KHz
>>> regardless of IF filter so I ended up selling the extra 13-KHz filter.
>>>
>>> ...
>>>
>>> 73, Ed - KL7UW
>> I really hope that this does not apply to received audio to the
>> headphones or loudspeaker!   I just purchased two FM filters (one for
>> sub-receiver to monitor wide splits) specifically to open up the receive
>> passband (audio included) for SWL and BCB reception. I have no intention
>> of actually transmitting FM or AM for that matter -- just want the wider
>> audio bandwidth for receive.
>>
>> So... is the received audio bandwidth *really* limited to 4 KHz?
>>
>
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