[Elecraft] K3: roofing filter configuration settings

[Bob McGraw K4TAX]

Filter bandwidth is defined by two points either across the top or at 
the knee of the filter.  If the knee is 250 Hz wide at the 3 dB points 
then measuring the 6 dB points may be 370 Hz wide.  So without the 
position of the filter where the measurement takes place, the number 
relating to bandwidth is inadequate to describe the filter.  There is 
really no standard with regard to filter measurements, thus the value is 
simply arbitrary.

Yes a given filter can be 250 Hz at the 3 dB points, can also be 370 Hz 
at the 6 dB points and also 500 Hz at the 18 dB points. So........what 
is the bandwidth of the filter?

73
Bob, K4TAX
K3S, s/n 10163



On 2/10/2016 5:49 AM, Arie Kleingeld PA3A wrote:
> Hi Dick,
>
> Just do it. If you need a certain bandwidth for a certain mode, use 
> the narrowest roofer you have in there; just like in any other 
> conventional transceiver.
> So if you want 350Hz as bandwidth, use that 250 filter (which is 
> actually 370). That's common sense.
> Don't let the 250Hz tag on the filter fool you. They say they sell you 
> 250Hz, that's just not true. It should have stated 350Hz or so.
>
> And in ham spirit: just try out different settings and decide what 
> works best.
>
> 73
> Arie PA3A
>
> Op 10-2-2016 om 6:05 schreef Dick via Elecraft:
>> snip>
>>   The factory default roofing filter "configuration bandwidth" 
>> setting  is to
>> set the 250hz filter at a setting of "250".  Therefore, the 250hz 
>> roofing
>> filter will engage at the same time as the 250hz DSP filter.
>> However, since the 250hz roofing filter has an actual BW6 of 370hz,  
>> aren't
>> there times when it would be more beneficial to have  the "configuration
>> bandwidth" of the 250hz roofing filter set to 350 or  400?
>> I'm thinking this may be especially true when operating RTTY since the
>> average RTTY bandwidth is aprx. 370hz.  Perhaps there are times when  
>> this
>> would be beneficial when operating other modes as well?
>>   <snip
>>   Dick- K9OM
>
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