[TenTec] 9Mhz filters

[Dave Sublette]

There was (is?) also the p/n221 filter.  It is centered at 9.000500 and 
is 250 hz BW. Using this filter results in a CW offset of 500 hz instead 
of the "industry standard" 750 hz offset. The lower offset is much 
easier on the ears and creates less fatigue from operating long hours in 
contests, etc. This filter has 14 dB loss and I'm wondering if this is 
useful as a roofing filter in the Orion?

I thought there was a corresponding 6 mhz, 250 hz filter to match the  
low offset 221 filter and I thought I had it in my OMNI VI+, but I can't 
find the invoice where I bought it. I found the invoice for all my other 
filters.  I do have a p/n 282, 6 mhz, 250hz BW filter in my VI+, 
according to my records. Perhaps this works with the low offset 9 mhz 
filter without a need for another filter at 6Mhz.

Dave, K4TO

Zivney, Terry L. wrote:

>Barry N1EU said:
>
>  
>
>>>Correct me if I'm wrong, but Bill is ordering filters
>>>      
>>>
>with a center frequency of 9.001500, which isn't what
>the Omni VI is looking for.
>
>Correctomundo, Barry!  But, 9.001500 isn't correct for
>the Orion, either.  The 9.001500 "standard" for
>wider TenTec filters is derived from the idea of
>
>0-300  stop band
>300-2700 pass band (i.e., 2400Hz bandwidth)
>2700-3000 stop band
>
>and the symmetry of switching sidebands by moving
>the BFO frequency 3 kHz.  If you get a center frequency
>of 9.001500 with a narrow bandwidth, 400, 500 or 600 HZ,
>you are assuming you want a CW tone of 1500Hz with
>a BFO of 9 MHz.  The correct center frequency for
>the narrow filter is 9.000750, which results in a 
>default CW pitch of 750 Hz, +/- the adjustment.
>
>In summary, I believe a better choice for a special
>order frequency is 9.000750, which would accomdate
>both Orion and OMNI VI users.
>
>Thanks for pointing out the offset problem.
>
>Terry ZIvney, N4TZ/9
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