Posted by
Don Wilhelm-4 on
Jul 20, 2011; 2:10am
URL: http://elecraft.85.s1.nabble.com/need-some-roofing-filter-advice-tp6581353p6601087.html
Ed is entirely correct.
Those who attempt to manipulate the shift and width to obtain an
intelligible response on SSB are creating more trouble than it is worth.
For maximum voice intelligibility, the low frequency corner of the
filter must remain at 300 Hz (or slightly lower). The high frequency
end can be cut drastically and the signal will still be intelligible.
Try it - set the Lo Cut to 250 or 300 Hz, and then reduce the HI-Cut to
narrow the bandwidth. You can achieve a very narrow bandwidth and still
maintain intelligibility.
I have been setting K2 SSB filters to achieve that same result for a
very long time. Cut the highs, but leave the lows in place, and you can
use a filter as narrow as 1500 Hz (or less) with excellent results.
73,
Don W3FPR
On 7/19/2011 9:51 PM, Ed Muns wrote:
> The K3 is entirely different. I've been operating SSB with a 1.5 kHz
> bandwidth for three years now and it is perfectly intelligible. On prior
> radios, though, I couldn't even get a 2.1 kHz filter to sound intelligible
> enough to be useful. I think the difference is where the filter is located
> relative to the signal. In the K3, narrow filtering on SSB sounds best if
> you simply reduce the HI CUT to get the desired bandwidth. If you first
> reduce the WIDTH, then you have to also adjust SHIFT to optimize
> intelligibility. (Note the word "intelligibility", not "high fidelity", the
> emphasis being on communication and the ability to copy.)
>
> You don't need to buy a crystal filter to try narrow SSB bandwidths. Just
> use the DSP HI CUT control. If you find a narrow SSB bandwidth you like to
> use regularly, AND also you need to protect the IF from very strong nearby
> signals, then consider a crystal filter of the appropriate bandwidth, ahead
> of the DSP.
>
> Ed - W0YK
>
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