K3 and spectrogram: dual passband

[Cloud Runner-3]

The dual passband on spectrogram was most informative.  It turns out my ear had little idea what was going on.

I have the 2.7 khz and the 500 khz (but the radio is set to 600 khz).  I think this function will act differently with different filters on board.

Here is what happens.  When one puts on "dual passband," the inner passband that is at full sensitivity is fixed at the 600 hz of the narrower roofing filter.  That PB does not change with any PB tuning adjustments.

The outside PB is about 25 DB down.  For me, that is too much!!!  I would rather this be down more like 15 DB.  At 25 DB down, I can hear there are stations outside the inner PB, but I can not copy them at the same time as the station in the center.

The outer PB is tipped, that is, the high frequency side of the inner filter is five to ten DB stronger than the low side.  Seems like it ought to be in balance.

PB shift or PB Hi / Lo cut, both do exactly the same thing when in dual PB mode.  They narrow up the outer filter, down to the inner filter at the narrowest.  They do not, for example, I might have thought the in HI /Lo mode, you might be able to chop off the upper or lower context independently, but you can not.

73,  Fred - kt5x

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[dave.wilburn]

Any screen shots?
-  

David Wilburn
[hidden email]
K4DGW
K2 S/N 5982


On Wed, 2007-12-26 at 20:18 -0700, cloud runner wrote:

> The dual passband on spectrogram was most informative.  It turns out my ear had little idea what was going on.
>
> I have the 2.7 khz and the 500 khz (but the radio is set to 600 khz).  I think this function will act differently with different filters on board.
>
> Here is what happens.  When one puts on "dual passband," the inner passband that is at full sensitivity is fixed at the 600 hz of the narrower roofing filter.  That PB does not change with any PB tuning adjustments.
>
> The outside PB is about 25 DB down.  For me, that is too much!!!  I would rather this be down more like 15 DB.  At 25 DB down, I can hear there are stations outside the inner PB, but I can not copy them at the same time as the station in the center.
>
> The outer PB is tipped, that is, the high frequency side of the inner filter is five to ten DB stronger than the low side.  Seems like it ought to be in balance.
>
> PB shift or PB Hi / Lo cut, both do exactly the same thing when in dual PB mode.  They narrow up the outer filter, down to the inner filter at the narrowest.  They do not, for example, I might have thought the in HI /Lo mode, you might be able to chop off the upper or lower context independently, but you can not.
>
> 73,  Fred - kt5x
>
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[KK7P]

> The outer PB is tipped, that is, the high frequency side of
> the inner filter is five to ten DB stronger than the low side.
>  Seems like it ought to be in balance.

I think if you plot the response at whatever width you have set, you'll
see the low frequency rolloff before you engage Dual PB.  This is likely
due to the relationship of the filter skirts and BFO.  If you then turn
on Dual PB, you'll see the former passband suppressed about 25 dB and
the 150 Hz wide peak rising above it.

Alternately, set the pitch higher to get away from the wide filter's
passband edge and you'll see the suppression is in fact symmetrical
about the peak.

73,

Lyle KK7P

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