[TenTec] Omni VI filters

[Ken Brown]

It is unclear to me whether you are talking about the NAR or N1, N2 filters
in the 9 MHz IF or the Filters in the 6.3 MHz Pass Band Tuning IF. In
either case there is something not quite right. If the S meter changes at
all between the 2.4 and 1.8 kHz filters it should decrease, not increase,
because of lower total power from lower bandwidth, and because narrower
filters almost always have higher loss.

In the 9 MHz IF there are jumpers that can be set to add attenuation for
wider filters, to sort of compensate for the higher loss you would get from
a narrower filter. It you are talking about 9 MHz filters, then you may
have a jumper in a wrong position.

It is also possible that you have a filter with a fault. Such as a bad
crystal or a cold solder joint. First thing I would do is remove the filter
and re-flow all of the solder connections on the filter. That could fix it.

In the 6.3 MHz Pass Band Tuning IF there are also attenuators on the wider
filters to compensate for higher losses in narrower filters. Those
attenuators are not changeable with jumpers. ( that would be because the
design intention was to always use the same 1.8, .5 and .25 filters from
Ten-Tec with known losses ) Those attenuators are hardwired in. R26, 27,
28, R31, 32, 33, R36, 37, 38 are the T pad attenuators on the wider three
filters.

DE N6KB


On Sun, Aug 6, 2017 at 7:34 PM, Stan Gammons <s_gammons at charter.net> wrote:

> On 08/06/2017 10:58 PM, Ken Brown wrote:
>
> The other thing that really matters is the spectral distribution of the
>> noise and signal power within the filter bandpass. For example if the
>> power
>> of the noise or the signal is distributed uniformly across the whole 2.4
>> kHz bandwidth of the filter, then it would be perfectly normal for the S
>> meter reading to drop by a factor of 1.8 / 2.4 when switching from the 2.4
>> kHz filter to the 1.8 kHz filter.
>>
>
> Hi Ken,
>
> The S meter does not drop when switching from 2.4 to 1.8  The S meter
> increases around 2 S units or so when going from 2.4 to 1.8 With the
> narrower 500 Hertz filter, the S meter is the same as it is with the 2.4
> filter.  Since I'm not familiar with the Omni VI, I don't know if it has
> any compensation for the narrow 2nd IF filters.  Guess I need to read the
> manual :)
>
>
>
> 73
>
> Stan
> KM4HQE
>
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