On Thu, May 1, 2014 at 9:38 PM, Bob McGraw - K4TAX <RMcGraw@blomand.net>wrote:
> Otherwise, if you live in an area 5 to 10 miles from town and the nearest
> ham does not operate on the same band the same time as you, then they
> aren't necessary but, certainly nice to have available.
>
>
As far as their minimal necessity - you need at least one roofing filter
installed to hear anything. And any signal wider than your widest roofing
filter will be attenuated outside the passband. So at minimum, install a
single roofing filter as wide as the widest signal(s) you want to listen to.
Hardware AGC kicks in by any signal on the band that is over ~ s9 +25dB, to
protect the DAC dynamic range. Roofing filters prevent AGC riding by such
a strong signal outside the passband. Signals of that strength are not
uncommon here on the east coast on the low bands, especially during
contests - also on 20M from European powerhouse contest stations. So
serious contesters and low band dx'ers DO need roofing filters.
73, Barry N1EU
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