Elecraft › [K3]

Fw: K-3 Roofing filter comment

Classic

List

Threaded

2 messages Options

Richard Fjeld

Fw: K-3 Roofing filter comment

I failed to CC the group.

----- Original Message -----
From: "Richard Fjeld" <[hidden email]>
To: <[hidden email]>
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" <[hidden email]>
> To: <[hidden email]>
> 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" <[hidden email]>
>> To: "Richard Fjeld" <[hidden email]>
>> Cc: "elecraft posting" <[hidden email]>
>> 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
>>>>
>>
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Don Wilhelm-4

Re: Fw: K-3 Roofing filter comment

And for those interested, this was my private reply to Dick:
--------------------------------------------------------------
Dick,

The only dumb questions are those that are not asked.
Yes, you most likely would have seen the same thing with the 5 pole
filter. I believe the DSP skirt goes to greater than 90 dB which is
about the limit of hearing, and it is close to straight sided. DSP can
produce almost an ideal filter shape - the limitations imposed are those
of the ADC and DAC used - the number computations done by the DSP engine
can be as perfect as the math.

73,
Don W3FPR

On 7/12/2011 3:13 PM, Richard Fjeld wrote:

> I failed to CC the group.
>
> ----- Original Message -----
> From: "Richard Fjeld"<[hidden email]>
> To:<[hidden email]>
> 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"<[hidden email]>
>> To:<[hidden email]>
>> 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"<[hidden email]>
>>> To: "Richard Fjeld"<[hidden email]>
>>> Cc: "elecraft posting"<[hidden email]>
>>> 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
>>>>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>