[TenTec] Omni Vi+ 1.8 kHz filter response (2nd IF @ 6.3 MHz)

[Barry N1EU]

filter info also at http://omni6.wikidot.com/filters

73 Barry N1EU

On Sat, Jan 5, 2019 at 8:23 PM Ken Brown <kenradiobrown at gmail.com> wrote:

> I made a fairly comprehensive list of Ten-Tec filter model numbers, stock
> numbers, bandwidths, etc. It has been posted on a website. Using only my
> phone it's too hard for me to find. If you don't find it sooner, I will
> tell you where to find in a few days when I get back to my PC. DE N6KB.
>
> On Fri, Jan 4, 2019, 18:38 Phil Erickson <phil.erickson at gmail.com wrote:
>
> > Hi all,
> >
> >   If this list will indulge a further curiosity:
> >
> >   With my VI+ back together, I measured the filter response of the two
> SSB
> > filters @ 2nd IF : the default one (2.4 kHz nominal) and the one that I
> > thought was 1.8 kHz (supposed to be Ten-Tec #288).
> >
> >   Procedure for each filter:
> >
> > - Injected a test tone from signal generator at a known frequency
> > - set the radio for LSB
> > - AGC off
> > - slowly move the tuning dial upwards 100 Hz at a time away from the
> > frequency
> > - record freq offset and approximate tone amplitude in V using a Tek
> scope
> > (1 Mohm input) clipped to the External Speaker leads
> > - plotted 20*log10(V) as a function of frequency
> >
> >   To my surprise, the 1.8 kHz has almost exactly the same response width
> as
> > the 2.4 kHz.  It makes me think that someone accidentally installed a 2.4
> > kHz in that position, as I definitely expected the 1.8 to be narrower.
> >
> >   Is there any marking on the standard TT filters that allows you to tell
> > them apart?  I couldn't find any, but I didn't lift the filters off the
> PBT
> > board to see the underside.  (I note with some interest as well that
> Inrad
> > didn't bother to make anything narrower than 2.1 kHz for the 2nd IF.  Was
> > SSB somewhat of an afterthought on this radio?)
> >
> > 73
> > Phil W1PJE
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> >
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