[Elecraft] Fw: K-3 Roofing filter comment

[Richard Fjeld]

I failed to CC the group.

----- Original Message ----- 
From: "Richard Fjeld" <rpfjeld at embarqmail.com>
To: <don at w3fpr.com>
Sent: Tuesday, July 12, 2011 2:03 PM
Subject: Fw: [Elecraft] K-3 Roofing filter comment


> Don,
> I realize that last reply seemed like a dumb question, but it's hard for 
> me to realize that the DSP can do that so well.
>
> Dick
>
> ----- Original Message ----- 
> From: "Richard Fjeld" <rpfjeld at embarqmail.com>
> To: <don at w3fpr.com>
> Sent: Tuesday, July 12, 2011 1:47 PM
> Subject: Re: [Elecraft] K-3 Roofing filter comment
>
>
>> That's beautiful. Thanks for explaining. I'm coming from the non-DSP 
>> world. (The 'old world'.)
>> So, would it have been the same with the 5 pole 2.7 Khz filter?
>>
>> 73, Dick n0ce
>>
>> ----- Original Message ----- 
>> From: "Don Wilhelm" <w3fpr at embarqmail.com>
>> To: "Richard Fjeld" <rpfjeld at embarqmail.com>
>> Cc: "elecraft posting" <elecraft at mailman.qth.net>
>> Sent: Tuesday, July 12, 2011 1:33 PM
>> Subject: Re: [Elecraft] K-3 Roofing filter comment
>>
>>
>>>  Richard,
>>>
>>> You were not hearing the effect of the 2.8 MHz roofing filter, but 
>>> instead the DSP filter.
>>> In order to hear the effect of the 2.8 kHz filter skirt, you would have 
>>> to widen out the DSP bandwidth to max or greater.  The DSP forms the 
>>> ultimate filter, and does have nearly vertical slope.
>>>
>>> The purpose of the roofing filter is to keep adjacent strong signals 
>>> from activating the hardware AGC and causing the resulting AGC pumping. 
>>> It is the DSP that sets the actual filter width.
>>>
>>> 73,
>>> Don W3FPR
>>>
>>> On 7/12/2011 2:22 PM, Richard Fjeld wrote:
>>>> FYI,
>>>> I don't want to open up a 'can of worms', and Rob Sherwood could better 
>>>> speak to this, but this is an observation I made using a P-3.
>>>>
>>>> Not long ago, there was quite a string of threads about the 5 pole 2.7 
>>>> Khz roofing filter versus the 8 pole 2.8 Khz filter. Before I ordered 
>>>> my K-3, I had studied the filter skirts of each. I don't remember how I 
>>>> found the plot for the 5 pole filter, but I remember that the span of 
>>>> each was different. At the same span width, the 2.8 Khz filter skirts 
>>>> seemed to me to be considerably straighter when compared to the 2.7 Khz 
>>>> filter, so I ordered the 2.8 filter.
>>>>
>>>> The other day, I was on a qso with a group and while watching the SSB 
>>>> signal on the P-3, I noticed a carrier much taller appear right on the 
>>>> edge of the filter bandwidth as shown by the brackets at the bottom of 
>>>> the P-3. The carrier was on the far end of the filter, or 2.8 Khz away 
>>>> from the center frequency.
>>>>
>>>> I could not hear it, but expected to, so I tuned over slightly to get 
>>>> it within the filter bandwidth and heard it strongly. I seem to recall 
>>>> that a filter's width is rated at something like 6 dB down, so I 
>>>> thought I would have heard it within the skirts at their wider limits. 
>>>> I still wonder about that, but I'm very pleased.
>>>>
>>>> (Just a comment; I'd hate to do without the P-3)
>>>>
>>>>
>>>> Richard Fjeld, n0ce
>>>>
>>
>