[Elecraft] K3 APF

[Joe Subich, W4TV]

>> I'll count this as another vote in favor of adding the Variable Q
>> setting...

Not on your life.  The lack of ringing on the newer version seems to
go along with a general decline in effectiveness.  If anything I'd
prefer to see higher Q.

Just for grins I reloaded 4.16 to make the same measurements using the
XG-2 as I made on 4.21.  Here is the comparison:

    BW     4.21   4.16
  -------------------------
    0 dB	    1  	   2   Hz
   -1 dB	    8	   9   Hz
   -6 dB	   31	  31   Hz
  -10 dB	   52	  49   Hz
  -20 dB	  165	 162   Hz
  -30 dB	  345	 351   Hz
    Gain	  9.0	 9.1   dB

Unlike W4ZV, I found only a 3 Hz offset in 4.16 (the peak response
was 3 Hz above zero beat - or the indicated spot/shift frequency).
Even though the test results were generally the same within the
measurement tolerances, I still feel the 4.16 version was more effective 
in on air listening.

These measurements were generated with an XG-2 set for 1 uV with the
K3 attenuator engaged for an effective signal level of -118 dBm.

73,

    ... Joe, W4TV

On 11/13/2010 8:07 PM, The Smiths wrote:
>
> I'll count this as another vote in favor of adding the Variable Q setting... At least a choice of 3 perhaps Wide, Med and Narrow.  Even if one perceives the APF as "less ringy" and comments on it being a good thing, that means that they are happy to know that the Q got widened out a little, and things seem to sound "better".
>
>> From: w5wvo at cybermesa.net
>> To: lists at subich.com; elecraft at mailman.qth.net
>> Date: Sat, 13 Nov 2010 21:19:46 +0000
>> Subject: Re: [Elecraft] K3 APF
>>
>> Joe wrote:
>>
>>> I did not make similar measurements with the original alpha
>>> test version but this version seems subjectively less tight
>>> than the original ... there is certainly less ringing with
>>> this one but signals did not seem to "pop" like they did on
>>> the earlier version when I tried it last night on 160/80/40.
>>
>> Joe, I agree with your subjective observation. No, the signals don't "pop"
>> as much -- but there is less ringing. This is a trade-off, of course, and
>> the precise balance of peak gain versus ringing is always going to be a
>> matter of personal preference.
>>
>> I like this less-ringy version better, I think. Haven't had time to play
>> with it a lot yet, but I will. I'm sure we will see many other opinions. So
>> far, I think the current version is very smooth and adequately "peaky".
>>
>> (Opinion subject to revision upon more extensive usage.)
>>
>> Bill W5WVO
>>
>>
>> -----Original Message-----
>> From: Joe Subich, W4TV
>> Sent: Saturday, November 13, 2010 20:35
>> To: elecraft at mailman.qth.net
>> Subject: Re: [Elecraft] K3 APF
>>
>>
>> I made a similar set of measurements ... using the XG-2 and
>> the AFV/dBV capability ...
>>
>> I measure the peak at 1 Hz wide (e.g. -.1dB +/- 1 Hz)
>> the 1 dB points are 8 Hz wide
>> the 6 dB points are 31 Hz wide
>> the 20 dB points are 165 Hz wide
>> the 30 dB points are 345 Hz wide
>> gain is right at 9 dB.
>>
>> The measurements were made on 40 Meters with the XG-2 set to
>> 1 uV and the K3 attenuator activated yielding a -108 dBm test
>> signal.
>>
>> I did not make similar measurements with the original alpha
>> test version but this version seems subjectively less tight
>> than the original ... there is certainly less ringing with
>> this one but signals did not seem to "pop" like they did on
>> the earlier version when I tried it last night on 160/80/40.
>>
>> 73,
>>
>> ... Joe, W4TV
>>
>>
>> On 11/13/2010 1:24 PM, Bill W4ZV wrote:
>>>
>>> For my own curiosity I did some measurements of the latest APF. They agree
>>> with
>>> measurements of the first release with the exception that the filter peak
>>> is
>>> now
>>> zero beat instead of +10 Hz:
>>>
>>> Zero beat = 7040.021
>>> Flat passband = 021-020 (both 0.0 to -0.1 dB)
>>> -1 dB passband = 026-018 (-1.2 dB and -0.8 dB)
>>> -6 dB passband = 037-009 (-5.8 and -6.0 dB)
>>>
>>> Flat = 2 Hz BW (at zero beat)
>>> -1 dB = 8 Hz BW
>>> -6 dB = 28 Hz BW
>>>
>>> I didn't measure the -6 dB BW carefully on the first pass since I was more
>>> interested in the -1 dB BW, but this looks similar and agrees with Lyle's
>>> 30
>>> Hz
>>> design goal. As mentioned previously, the -1 dB BW is important when
>>> trying
>>> to
>>> detect signals below the noise floor since the human ear can detect this
>>> difference in marginal conditions.
>>>
>>> I also checked the gain (APF vs not) which I didn't do before...+9.1 dB
>>> which is
>>> very close to Lyle's design goal of +9 dB.
>>>
>>> Nice job Elecraft!
>>>
>>> 73, Bill
>>>
>>>
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