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

[Ken Brown]

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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