[Elecraft] K3 - Filter suggestions for new builder

[Dale Boresz]

Joe,

Understood. I wanted to be able to simultaneously hear and see 12 Khz or 
so of cw signals, thinking that I could more quickly identify the 
station being worked. For example, if I know the dx station is listening 
from 14.010 to 14.020 (admittedly pretty wide), I figured I could 
include that entire range within the FM filter bandwidth (which I still 
can do), AND also hear all 10 KHz of those signals (which I've learned I 
cannot do). Oh well; the FM filter will still let me hear a wider swath 
of the pile-up than my present 2.8KHz filter will...

73, Dale
WA8SRA


On 9/26/2012 9:25 PM, Joe Subich, W4TV wrote:
>> 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),
> The width of the roofing filter has nothing at all to do with hearing
> more of the pile-up (unless you're talking about literally "listening"
> to all the signals at one time like a pile-up tape).  The P3's pick-
> up point is ahead of any roofing filter - it can "see" up to 200 KHz
> at a time.  The K3 transmitter and receiver can be split anywhere in
> the band and if the KRX3 is used with a separate antenna the K3 and
> KRX3 can literally transmit on one band and listen on another.
>
> 73,
>
>      ... Joe, W4TV
>
>
> On 9/26/2012 8:58 PM, Dale Boresz wrote:
>> 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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