[Elecraft] K3:New APF what happened?

Steve Ellington n4lq at carolina.rr.com
Wed Nov 17 17:36:01 EST 2010


Bill:

Nice job. I figured all along it was either due to a brain problem or being 
female.

Steve N4LQ


----- Original Message ----- 
From: "Bill VanAlstyne W5WVO" <w5wvo at cybermesa.net>
To: "Bill W4ZV" <btippett at alum.mit.edu>; <elecraft at mailman.qth.net>
Sent: Wednesday, November 17, 2010 2:45 PM
Subject: Re: [Elecraft] K3:New APF what happened?


> Very good summary of the technical facts, Bill.
>
> It's IMPULSE noise, everybody, not white noise or pink noise or any other
> kind of noise. Impulse noise is characterized by a very rapid transient
> rise-time producing a large nearly instantaneous spike in amplitude. It's
> literally the electrical equivalent of striking a bell sharply, as opposed
> to rubbing it.
>
> The other thing that can make this feature seem magical (in the absence of
> excessive ringing) is having it properly tuned, and by "properly" I mean
> within a few Hertz. The K3's CWT/SPOT capability is good, but it's often 
> not
> good enough for this degree of accuracy. Mine usually tunes to within +/- 
> 10
> Hz, but that's not always close enough for the APF to work at its best. 
> The
> signal needs to be fine-tuned by ear, IMO, against the sidetone PITCH
> frequency. Most people can hear the difference between two tones down to 1
> Hz or less. (BUT, some people CAN'T. It's a brain thing. Your brain can
> either do this or it can't. My XYL couldn't do this if her life depended 
> on
> it, as she is completely tone-deaf.)
>
> So maybe we can agree that there are a lot of variables at work here that 
> we
> can't control for. I thought at first that the current release was "less
> ringy" than the earlier release; I was fooled by a difference in band 
> noise.
> Since then, I've seen the APF feature behave quite differently on 
> different
> bands at different times. So, if it makes it easier to copy a given 
> signal,
> use it, and if it doesn't, leave it turned off. It's a tool. All tools are
> not appropriate for all jobs all the time. You have to choose your tools 
> and
> when to use them.
>
> Bill W5WVO
>
>
>
> -----Original Message----- 
> From: Bill W4ZV
> Sent: Wednesday, November 17, 2010 15:35
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3:New APF what happened?
>
>
>
> N2TK wrote:
>>
>> John,
>> Maybe the impact of the APF is a moving target influenced by the band
>> conditions at the time?
>> Yesterday morning 160M was very quiet. I could not hear the VK6 without
>> the
>> APF. When I turned on the APF the VK6 popped out of the band noise and 
>> was
>> easily copyable. There was no hint of ringing even with the bandwidth 
>> down
>> to 50HZ.
>>
>> Last night as usual in the evenings here 160M was noisy. When I turned on
>> the APF it still did its magic. But there was almost a trace of 
>> "ringing".
>>
>> I need to play more with it to see if it is a definite pattern comparing
>> between quiet and noisy band conditions.
>>
>
> Ringing is a function of how much impulse noise (i.e. lightning induced,
> electric fencer "ticks", key clicks, etc) hits the filter.  No impulse 
> noise
> = no ringing,  lots of impulse noise = continuous ringing.  As you said,
> yesterday morning 160m was stone quiet and the background noise was
> non-impulsive or white noise.  Last night a strong cold front moved across
> the Southeastern states which had lightning associated with the front. 
> The
> lightning strikes created impulse noise which caused the filter to ring 
> more
> than in the morning.  This effect is present in any narrow filter, whether
> analog or digital, and there's really not much that can be done to avoid 
> it.
> Reducing AF Gain is about the only solution to attenuate the continuous
> ringing sound but that also attenuates the signal you're trying to hear.
>
> 73,  Bill
> -- 
> View this message in context:
> http://elecraft.365791.n2.nabble.com/RX-architecture-tp5746603p5748164.html
> Sent from the Elecraft mailing list archive at Nabble.com.
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