[Elecraft] K3 - Filter suggestions for new builder

[Dale Boresz]

Joe,

Good observations, all. I agree that 4.2 KHz is certainly good enough 
for communications audio.

The only reason I had for putting the FM filter in the 2nd receiver was 
to be able to hear more of the split in a broad pileup situation (like 
the extremely large split widths that we saw a few months ago with 
7O6T), figuring that being able to simultaneously hear the wider 
bandwidth and see it on the P3 would be a great combination. I'll just 
have to be a bit quicker with the VFO-B knob  ;-)

73, Dale
WA8SRA


On 9/26/2012 8:10 PM, Joe Subich, W4TV wrote:
> 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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