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HaroldZ, Variable bandwidth filter, etc

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William Carver

HaroldZ, Variable bandwidth filter, etc

What is the two tone dynamic range of the K3 when both signals are
inside the roofing filter bandwidth?

Close-in IMD measurements are virtually always done using a CW bandwidth
filter. None of the published data (ARRL, Sherwood Engineering) tests
IMD inside the DSP process without xtal filter selectivity.

My experience with a homebrew K3-like topology, except a strong diode
second mixer (instead of NE602-type mixer), is the limiting factor
INSIDE THE ROOFING FILTER bandwidth can be the DSP performance. If you
put a FLEX DSP processor behind a K3 2.8 KHz SSB filter you would have
FLEX numbers close in, K3 numbers outside the roofing filter. The
advantages of both.

So rather than bandaid by buying more filters, or push for a variable
filter, if the dynamic range inside the filter is not good enough one
should concentrate on (1) strengthening the post-xtal-filter intercept
of the receiver circuits and (2) reducing the close-in phase noise of
the LO.

Bill - W7AAZ

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Joe Subich, W4TV-4

Re: HaroldZ, Variable bandwidth filter, etc

> What is the two tone dynamic range of the K3 when both
> signals are inside the roofing filter bandwidth?
>
> Close-in IMD measurements are virtually always done using a
> CW bandwidth filter. None of the published data (ARRL,
> Sherwood Engineering) tests IMD inside the DSP process
> without xtal filter selectivity.

With roofing filters that are matched to the appropriate bandwidth
for the operating mode dynamic range inside the roofing filter is
not a consideration. Once the interfering signal gets inside the
roofing filter, it's interference and nothing is going to get rid
of it.

For example, the point of a 200 Hz filter is not so much to reduce
IMD (remember the interfering signals need to be 200 Hz and 400 Hz
(or 300 Hz and 600 Hz, etc. away to cause IMD "on frequency") but
to prevent close in signals from effecting AGC, etc. As Rob Sherwood
has said many times, the problem with close in interference is just
as likely to be "dirty" signals (phase noise, key clicks, and
transmitter IMD) as it is to be receiver effects as long as the
dynamic range is 90 dB or more.

73,

... Joe, W4TV

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of William Carver
> Sent: Thursday, August 06, 2009 9:56 PM
> To: [hidden email]
> Subject: [Elecraft] HaroldZ, Variable bandwidth filter, etc
>
>
> What is the two tone dynamic range of the K3 when both
> signals are inside the roofing filter bandwidth?
>
> Close-in IMD measurements are virtually always done using a
> CW bandwidth filter. None of the published data (ARRL,
> Sherwood Engineering) tests IMD inside the DSP process
> without xtal filter selectivity.
>
> My experience with a homebrew K3-like topology, except a
> strong diode second mixer (instead of NE602-type mixer), is
> the limiting factor INSIDE THE ROOFING FILTER bandwidth can
> be the DSP performance. If you put a FLEX DSP processor
> behind a K3 2.8 KHz SSB filter you would have FLEX numbers
> close in, K3 numbers outside the roofing filter. The
> advantages of both.
>
> So rather than bandaid by buying more filters, or push for a
> variable filter, if the dynamic range inside the filter is
> not good enough one should concentrate on (1) strengthening
> the post-xtal-filter intercept of the receiver circuits and
> (2) reducing the close-in phase noise of the LO.
>
> Bill - W7AAZ
>
>
>
>
>
>
> ______________________________________________________________
> 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

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Steve Ellington

Re: HaroldZ, Variable bandwidth filter, etc

Joe et. al.
Someone mentioned combining the Flex I/Q mixer with the roofing filters of
the K3. I've noticed Icom started using the I/Q mixer with the IC-7800,
IC-7700 and now the IC-7600. This seems to be how they can get by with only
a broad skirted 3 kHz roofing filter and still have respectable performance.
I'm wondering what it would be like if Elecraft did use a similar DSP but
with narrow xtal filters ie. 200 Hz? It does sound like a good mix but I'm
no expert on DSP.
Steve
N4LQ
[hidden email]
----- Original Message -----
From: "Joe Subich, W4TV" <[hidden email]>
To: <[hidden email]>
Sent: Thursday, August 06, 2009 11:47 PM
Subject: Re: [Elecraft] HaroldZ, Variable bandwidth filter, etc

>
>> What is the two tone dynamic range of the K3 when both
>> signals are inside the roofing filter bandwidth?
>>
>> Close-in IMD measurements are virtually always done using a
>> CW bandwidth filter. None of the published data (ARRL,
>> Sherwood Engineering) tests IMD inside the DSP process
>> without xtal filter selectivity.
>
> With roofing filters that are matched to the appropriate bandwidth
> for the operating mode dynamic range inside the roofing filter is
> not a consideration. Once the interfering signal gets inside the
> roofing filter, it's interference and nothing is going to get rid
> of it.
>
> For example, the point of a 200 Hz filter is not so much to reduce
> IMD (remember the interfering signals need to be 200 Hz and 400 Hz
> (or 300 Hz and 600 Hz, etc. away to cause IMD "on frequency") but
> to prevent close in signals from effecting AGC, etc. As Rob Sherwood
> has said many times, the problem with close in interference is just
> as likely to be "dirty" signals (phase noise, key clicks, and
> transmitter IMD) as it is to be receiver effects as long as the
> dynamic range is 90 dB or more.
>
> 73,
>
> ... Joe, W4TV
>
>
>
>> -----Original Message-----
>> From: [hidden email]
>> [mailto:[hidden email]] On Behalf Of William Carver
>> Sent: Thursday, August 06, 2009 9:56 PM
>> To: [hidden email]
>> Subject: [Elecraft] HaroldZ, Variable bandwidth filter, etc
>>
>>
>> What is the two tone dynamic range of the K3 when both
>> signals are inside the roofing filter bandwidth?
>>
>> Close-in IMD measurements are virtually always done using a
>> CW bandwidth filter. None of the published data (ARRL,
>> Sherwood Engineering) tests IMD inside the DSP process
>> without xtal filter selectivity.
>>
>> My experience with a homebrew K3-like topology, except a
>> strong diode second mixer (instead of NE602-type mixer), is
>> the limiting factor INSIDE THE ROOFING FILTER bandwidth can
>> be the DSP performance. If you put a FLEX DSP processor
>> behind a K3 2.8 KHz SSB filter you would have FLEX numbers
>> close in, K3 numbers outside the roofing filter. The
>> advantages of both.
>>
>> So rather than bandaid by buying more filters, or push for a
>> variable filter, if the dynamic range inside the filter is
>> not good enough one should concentrate on (1) strengthening
>> the post-xtal-filter intercept of the receiver circuits and
>> (2) reducing the close-in phase noise of the LO.
>>
>> Bill - W7AAZ
>>
>>
>>
>>
>>
>>
>> ______________________________________________________________
>> 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
>
> ______________________________________________________________
> 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