[Elecraft] Roofing Filters - An Empirical Test

[Wayne Burdick]

I should have pointed out that this effect is most noticeable with CW or narrow data modes, where there's a large difference in bandwidth between "wide" and "narrow" filters. In SSB mode, a somewhat narrower filter (say 1.8 kHz) will provide additional margin on an active band with strong signals, but some of the advantage is lost due to IMD products inherent in the received voice signals.

Wayne


On May 12, 2014, at 1:19 PM, Wayne Burdick <n6kr at elecraft.com> wrote:

> It's quite simple. If you have a very strong interfering signal that falls inside the SSB filter passband (2.7 or 2.8 kHz), but outside an installed narrow filter, the hardware AGC will not get "pumped".
> 
> Lacking such a filter, a strong enough signal (typically S9+20 or higher) *will* activate hardware AGC, which can be annoying in mild cases and debilitating if it's really strong, has key clicks, etc.
> 
> This is why the K3 has slots for narrow filters. On a very busy band with lots of strong signals, it's the difference between a usable radio or not. 
> 
> 73,
> Wayne
> N6KR
> 
> On May 12, 2014, at 12:54 PM, "Dauer, Edward" <edauer at law.du.edu> wrote:
> 
>> I would be interested in knowing if anyone has done an empirical test and
>> observed the difference directly.  Specifically, since the sub receiver is
>> identical to the main receiver in every way, if someone has a K3 with, for
>> example, a 400 Hz filter in the main but only a wider set in the sub, and
>> then set the DSP bandwidth on both receivers to 200 Hz or so, what
>> differences they actually noticed.  I have no doubt the theory and the
>> engineering are sound - just curious what the difference sounds like in
>> the field . . . 
>> 
>> Ted, KN1CBR
>> 
> 
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