[Test-Equipment] Q and filters

[Carl]

----- Original Message ----- 
From: "David" <davidwhess at gmail.com>
To: "Discussion of Electronic Test Equipment" 
<test-equipment at mailman.qth.net>
Sent: Sunday, June 22, 2014 5:12 PM
Subject: Re: [Test-Equipment] Q and filters


>I do not disagree.  I am just saying that poor phase response is a choice 
>when
> designing bandpass filters and this can be traded off for filter shape. 
> Linear
> phase response bandpass filters respond to an impulse with an output that 
> has a
> symmetrical envelope which could be considered to have less ringing but 
> like you
> say, the uncertainty is still there.



** The uncertainy does become evident to the ear in favor of the LC in 
actual receiving tests. Signals do have to be strong to compare filter types 
and at some higher level even the LC will ring.


>
> For voice applications this is irrelevant (unless a high Q section 
> overloads)
> but for data communications it can be important.  I believe the reason 
> phasing
> type modulators and demodulators have better voice characteristics is that 
> the
> channel had to be better designed anyway to preserve the amplitude and 
> phase
> response.

** Im not sure what you are saying there. The audio phase shift network is 
not that complicated but requires precision components that were available 
in the 1950's on special order. The RF network is less complicated but 
requires care to set up and they do drift with age. With modern components 
it is rather easy to rebuild the audio part and some SS can replace tubes in 
the RF section and most everybody can afford better test equipment than what 
was available even to labs back then.

Fast forward to 2014 and you find SDR's using phasing again and with far 
more precision, reliability, and stability.

Carl



>
> On Sun, 22 Jun 2014 19:18:06 +0000, you wrote:
>
>>  Some how folks confuse linear phase response, bandpass ripple and 
>> ringing.
>>Mathematically, you can't avoid ringing with narrow bandpass. You don't 
>>even have
>>to use resonance to determine this. Just understanding simple Fourier 
>>transform.
>>  Fortunately both analysis agree. In fact one analysis leads to 
>> Heisenberg's uncertainty
>>principle.
>>Delta F= bandwidth
>>Delta T= time resolution or ringing so to speak
>> delta F x delta T > 1, then using Plank's constant E=hF and simple 
>> algebra you get
>> delta E x Delta T>h published in Heisenberg's first paper on the subject.
>>This can be used to derive the relationship of position and momentum
>>
>>73
>>Bill wa4lav
>>
>>From: Test-Equipment [test-equipment-bounces at mailman.qth.net] on behalf of 
>>David [davidwhess at gmail.com]
>>Sent: Sunday, June 22, 2014 1:58 PM
>>To: Discussion of Electronic Test Equipment
>>Subject: Re: [Test-Equipment] Q and filters
>>
>>From what I remember, the tradeoff is high Q versus higher order.  For a 
>>given
>>bandwidth the two can be traded off and the later will yield a lower Q per
>>section and cleaner phase response.
>>
>>On Sun, 22 Jun 2014 08:34:46 -0700, you wrote:
>>
>>>Hello Carl,
>>>
>>>~ Ive built several of his passive filters to get rid of high frequency
>>>hiss, they work great compared to noisy and distorted active filters.
>>>
>>>What I can't quite believe is that it's possible to build a narrow 
>>>passband
>>>filter (high Q?) without ringing. Am I missing something here?
>>>
>>>Cheers,
>>>
>>>Brian
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