[Elecraft] K3 - Filter suggestions for new builder

Dale Boresz dmb at lightstream.net
Thu Sep 27 07:05:16 EDT 2012 

No, I'm not a human 'Skimmer' -- but I can pick out an individual cw 
signal within about an 8 KHz span if it's pitch falls somewhere between 
about 200 Hz and 8 KHz, and can probably 'guestimate' by the pitch, to 
which signal it corresponds on the P3, and then quickly place my TX 
signal nearby and make my call.

I guess I'm not conveying very successfully what I was hoping to do. I 
can do this easily w/ the second rx of the FLEX-5K --  but we're talking 
completely different architectures, each with their own pluses and 
minuses. The FM filters and the KRX3 will be here today, so I'll be able 
to experiment soon enough. I suspect that just being able to monitor 
both the dx and the pile-up simultaneously will be a huge help, and I 
may not feel the need for such a wide bandwidth on the pile-up side. 
We'll see...

73, Dale
WA8SRA



On 9/27/2012 12:20 AM, Joe Subich, W4TV wrote:
>> 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).
> Your ears are much better than mine if you can actually copy a full
> 10 KHz wide audio pile-up.  I have enough trouble keeping up with
> 4 KHz or so (200 Hz to 4.2 KHz) if I open everything up in SSB mode.
> Note the K3 limits HI in CW to "Pitch + 1400 Hz" thus if one likes
> a 500 Hz tone, the highest frequency passed in CW is 1900 Hz.  The
> *widest* bandwidth possible in CW is by using an 800 Hz sidetone
> which results in 2.2 KHz ... whether the "roofing filter" is 2.7,
> 2.8, 6 or 13 KHz wide.
>
> 73,
>
>      ... Joe, W4TV
>
>
> On 9/26/2012 9:46 PM, Dale Boresz wrote:
>> 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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