[GreenKeys] filters, dead or alive

[Lee Mushel]

You know, folks, your talk of the ST-6 and passive vs. active filters is
making me feel that I have progressed so far into my declining years that
it's almost depressing!
I can remember spending fully three years before I was even able to locate a
machine for sale in some reasonable driving distance. And 88Mh toroids
(known as "zeroids" to my xyl) were something to treasure.   When the ST-6
first appeared, first as bare boards, as I'm sure a lot of you remember, I
bought the ones I felt I needed and incorporated them into my own version of
the "ultimate TU."   That  project actually landed a job for me in 1974
since it demonstrated that I did know something about electronic
construction.  I do find all of this discussion to be extremely interesting.
And I did see my "tuning fork" frequency reference the other day when
digging around in my shed for things I can use on new projects.   And I do
not recall "tuning" to be pleasurable. And, yes, I do find the fact that ham
radio has dramatically changed saddening, indeed.

And, Don, your Model 43 manual is sitting beside me along with a new box and
as soon as I find some panic reason to drive to the Post Office it will be
returned, along with my considerable gratitude and thanks!

Lee    K9WRU
----- Original Message -----
From: "David Freeman" <ww8s at zoomshare.com>
To: <GreenKeys at mailman.qth.net>
Sent: Monday, July 17, 2006 7:55 AM
Subject: Re: [GreenKeys] filters, dead or alive


> My experience was the opposite. I always had better luck with passive
filters than active filters way back when I was building experimental TUs.
Perhaps it was just my lack of ability but I found that active filters tuned
with a Q equal to passive filters would "ring" on static crashes causing
more printing errors. That said, the Dovetrons don't use LC circuits and
they work very well. I'm sure most newer TU designs don't use LC circuits
either.
>
> Dave, WW8S
>
>
>
>
> On Sun 7/16/2006  7:52 PM, "WB6BLV" <wb6blv at inreach.com> wrote :
>
> > I notice that most here seem to run passive filters
> > rather than active ones using op amps.  Is there
> > some advantage to using these older LC circuits?
> > For me it has always been much easier to just
> > adjust a single pot to set the filter right on the money.
> > Filter gain, Q, and of course center frequency are all
> > set with ease in most active filters, using three resistors.
> >
> > For MARS I had a set of passive filters made by
> > Grant Storey, and they worked well, but not as well as
> > simple active filters.
> >
> > Sidenote -  yes actual shift is the critical parameter for
> > HF vice actual frequency for VHF AFSK.  That is why
> > the URA-8A (CV-89) will work well on HF using the
> > lower in frequency tone pairs.  Anybody running the 89
> > in diversity mode?  Getting dizzi from the 'flippin line'?
> >
> > John
> > WB6BLV at inreach.com
> >
> > _______________________________________________
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> > http://mailman.qth.net/mailman/listinfo/greenkeys
> >
> >
> >
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