Prev: Difference between pi/4 QPSK and pi/4 DQPSK
Next: Achieving 'equal loudness' for A/B testing
From: glen herrmannsfeldt on 27 May 2010 15:48
Tim Wescott <tim(a)seemywebsite.now> wrote:
> On 05/27/2010 11:14 AM, BobG wrote:
>> Whats the rule of thumb for how far to detune the two outside filters
>> for third octave bandwidth?
(snip)

> It sounds like you're trying to make a filter in 2010 using design rules
> from 1940. There's nothing inherently bad in this, but there are
> certainly faster ways.

When I bought my first FM tuner 30 years ago (which I still have,
though don't use so much), I was told that I would have to retune
the IF every some number of years. Of course I never did that,
though I did buy the service manual for it.

Does anyone tune the IF section of FM tuners to correct
for any drift? (Especially after 30 years.)

-- glen
From: glen herrmannsfeldt on 27 May 2010 15:54
Jerry Avins <jya(a)ieee.org> wrote:
(snip)

> Do you perhaps have analog filters in mind? The design procedures for
> digital filters don't usually go in that direction.

There not being a comp.asp newsgroup, it seems that analog
questions end up here.

When I was in high school I had my grandfather's Heathkit
vacuum tube amplifier and tuner to play with. I have written
about them before, the preamp that is powered by the amplifier
through an octal socket connector. Among other features,
there are about four choices for phono equalization,
though I was reminded that RIAA was always the right one.
(I never tried to find any really old records.)

-- glen
From: Steve Pope on 27 May 2010 15:57
glen herrmannsfeldt <gah(a)ugcs.caltech.edu> wrote:

>Does anyone tune the IF section of FM tuners to correct
>for any drift? (Especially after 30 years.)

Sure. Tune precisely to a strong RF signal, and trim the
little IF filters until you see a maximum at their output
on a scope.

I haven't done this for maybe 40 years but that doesn't
mean it isn't still done....


S.
From: Jerry Avins on 27 May 2010 16:30
On 5/27/2010 3:57 PM, Steve Pope wrote:
> glen herrmannsfeldt<gah(a)ugcs.caltech.edu> wrote:
>
>> Does anyone tune the IF section of FM tuners to correct
>> for any drift? (Especially after 30 years.)
>
> Sure. Tune precisely to a strong RF signal, and trim the
> little IF filters until you see a maximum at their output
> on a scope.

That gets you maximum sensitivity at the expense of distortion at higher
volumes. Low distortion is achieved by stagger tuning to broaden the
response. This is best done with a sweep generator, but if one is good
at it (I was once) it can be done fairly well by ear.

> I haven't done this for maybe 40 years but that doesn't
> mean it isn't still done....

It's been longer than that for me.

Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
From: Jerry Avins on 27 May 2010 16:31
On 5/27/2010 3:29 PM, Tim Wescott wrote:
> On 05/27/2010 12:25 PM, Jerry Avins wrote:
>> On 5/27/2010 2:14 PM, BobG wrote:
>>> Whats the rule of thumb for how far to detune the two outside filters
>>> for third octave bandwidth? Is the middle filter supposed to have a
>>> little less gain to flatten the passband out? Is the Q of all 3
>>> filters the same? Do the skirts roll off at 18dB per octave? (I
>>> searched for 'triple tuned' but no hits, so I hope I dont get flamed
>>> for asking)
>>
>> Do you perhaps have analog filters in mind? The design procedures for
>> digital filters don't usually go in that direction.
>>
>> I remember doing the math for stagger-tuned IF strips in the early
>> 1050s. It wasn't all that hard, but I don't remember off hand. There's
>> an old paper in the Proceedings of the IRE.
>
> Whoa! Jerry, I knew you were old, but I didn't realize you were _that_
> old. For that matter, I didn't realize that they were building IF strips
> in the middle ages.
>
> Were you in England for the Battle of Hastings? What was it like?

Oops!

Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
First  |  Prev  |  Next  |  Last
Pages: 1 2 3
Prev: Difference between pi/4 QPSK and pi/4 DQPSK
Next: Achieving 'equal loudness' for A/B testing