K3/K3s filter setting with the K3 Utility

[Gary Smith-2]

It seems as intuitive, the filter you use
is the value you select in the K3 utility
under filter configuration. I.e. a 1.8
filter is set at 1.8 in the utility.

Considering there is DSP simultaneously
occurring at the same time;

Is there any advantage to setting the 1.8
above, say as 2. in the utility.

Or to have the 200Hz filter engaged at say
250?

If so, what benefits might be seen by
doing this?

Thanks,

73,

Gary
KA1J
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[Richard Ferch-2]

There can be reasons to configure a roofing filter differently from its
nominal bandwidth.

For example, I have a "250 Hz" filter. According to the filter plots on the
Elecraft web site, the 6 dB bandwidth of this filter is actually closer to
375 Hz. I configured my filter to switch in at 350 Hz, which makes it much
more useful to me than it would be if I had configured it to switch in at
250 Hz.

If this filter is configured to switch in at 250 Hz in agreement with the
label, then when you set your DSP bandwidth to 300 Hz or 350 Hz, you will
be using the next wider filter in your receiver. Strong signals outside the
DSP bandwidth but inside the wider  roofing filter's bandwidth can still
have bad effects, whereas if the filter is configured to switch in at 350
Hz, you can take advantage of its ability to reduce those unwanted signals
with relatively minor impact on signals within the DSP bandwidth.

Of course, if the bandwidth of the 250 Hz filter really was 250 Hz,
configuring it to switch in at 350 Hz would render the 300 Hz and 350 Hz
settings of the DSP filter somewhat less useful, since the actual bandwidth
of the filter combination would now be close to 250 Hz regardless of what
the DSP control said.

There might be reasons to go in the other direction as well, i.e. to
configure a filter to switch in only at a narrower bandwidth than the
bandwidth marked on the filter. For example, if you had 500 Hz and 1000 Hz
filters and often used a digital mode whose bandwidth was, say, 750 Hz, you
could configure the 1000 Hz roofing filter to switch in only at 700 Hz and
below. This would give you better filtering between 500 Hz and 700 Hz than
without the 1000 Hz filter, while still permitting the 750 Hz mode signals
to pass through at DSP settings of 750 Hz and above without being
restricted by the roofing filter.

73,
Rich VE3KI


KA1J wrote:

Is there any advantage to setting the 1.8
above, say as 2. in the utility.

Or to have the 200Hz filter engaged at say
250?
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[Richard Ferch-2]

I muffed the last part of my previous message, didn't I? Still, there are
some higher-order effects that might push someone into configuring a
roofing filter ti switch in at a slightly narrower setting than you might
at first expect.

73,
Rich VE3KI
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[Richard Ferch-2]

Earlier I gave an example of a situation where you might choose to enable a
roofing filter at a bandwidth wider than the bandwidth marked on the
filter. I also gave a poor example of enabling a filter at a narrower
bandwidth. Here is a better one:

You use a variety of digital modes with different bandwidths, one of which
happens to be the same as or close to the bandwidth of one of your roofing
filters. You find that when that roofing filter is engaged, that particular
digital mode does not decode as well as it does with a wider filter
setting. You might find that changing the configuration to switch that
filter in at a narrower setting allows that particular mode to decode well,
without having a noticeable adverse effect on the next narrower bandwidth
mode you normally use. The likelihood of all this happening in combination
with an actual need for a tight roofing filter because of nearby very
strong signals might be quite low, but there is at least a theoretical
possibility of such a scenario. There are probably more likely situations -
just pointing out that it is not impossible that someone might want to do
this. The good thing is, the capability is there if you somehow find that
you need it.

73,
Rich VE3KI
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[Rich-4]

Since we are on this topic.  I have a question regarding the 500hz
filter.   From what I have read it is rated at 525hz.   So would it be
best configured to come on at 500hz or should I set it to 550hz.  I do
not think you can set it to 525hz

Thanks in advance

Rich

K3RWN

On 3/22/2019 17:58 PM, Richard Ferch wrote:

> There can be reasons to configure a roofing filter differently from its
> nominal bandwidth.
>
> For example, I have a "250 Hz" filter. According to the filter plots on the
> Elecraft web site, the 6 dB bandwidth of this filter is actually closer to
> 375 Hz. I configured my filter to switch in at 350 Hz, which makes it much
> more useful to me than it would be if I had configured it to switch in at
> 250 Hz.
>
> If this filter is configured to switch in at 250 Hz in agreement with the
> label, then when you set your DSP bandwidth to 300 Hz or 350 Hz, you will
> be using the next wider filter in your receiver. Strong signals outside the
> DSP bandwidth but inside the wider  roofing filter's bandwidth can still
> have bad effects, whereas if the filter is configured to switch in at 350
> Hz, you can take advantage of its ability to reduce those unwanted signals
> with relatively minor impact on signals within the DSP bandwidth.
>
> Of course, if the bandwidth of the 250 Hz filter really was 250 Hz,
> configuring it to switch in at 350 Hz would render the 300 Hz and 350 Hz
> settings of the DSP filter somewhat less useful, since the actual bandwidth
> of the filter combination would now be close to 250 Hz regardless of what
> the DSP control said.
>
> There might be reasons to go in the other direction as well, i.e. to
> configure a filter to switch in only at a narrower bandwidth than the
> bandwidth marked on the filter. For example, if you had 500 Hz and 1000 Hz
> filters and often used a digital mode whose bandwidth was, say, 750 Hz, you
> could configure the 1000 Hz roofing filter to switch in only at 700 Hz and
> below. This would give you better filtering between 500 Hz and 700 Hz than
> without the 1000 Hz filter, while still permitting the 750 Hz mode signals
> to pass through at DSP settings of 750 Hz and above without being
> restricted by the roofing filter.
>
> 73,
> Rich VE3KI
>
>
> KA1J wrote:
>
> Is there any advantage to setting the 1.8
> above, say as 2. in the utility.
>
> Or to have the 200Hz filter engaged at say
> 250?
> ______________________________________________________________
> Elecraft mailing list
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> Please help support this email list: http://www.qsl.net/donate.html
>

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[K7TV]

If I understand correctly what Rich is saying, it could be exemplified like
this: "If you want e.g. a 2.1 kHz bandwidth to receive a digital signal, and
use a 2.1 kHz roofing filter in addition to a DSP setting of 2.1 kHz, you
may find that it won't decode as well as using a 2.8 kHz roofing filter
along with the 2.1 kHz DSP setting." That reminds me of what I have
sometimes imagined observing in receiving SSB. This may be just my
imagination, but I thought the voice sounded bad if I set the DSP to the
same width as the roofing filter. I have used the utility to make sure the
roofing filter is always at leas slightly wider than the DSP setting. Since
that change I have been much happier with SSB receive voice quality. Is this
just in my head? Flames accepted. If I am right, it suggests that the
crystal filters somehow have a negative effect on voice quality. My guess
would be that this comes from phase non-linearity at the edges of the
crystal filters. Haven't we heard that Elecraft checks/selects roofing
filters to ensure minimal phase distortion? Of course, the phase distortion
would negatively affect digital signal demodulation as well.

73,
Erik K7TV

-----Original Message-----
From: [hidden email] <[hidden email]> On
Behalf Of Richard Ferch
Sent: Friday, March 22, 2019 4:06 PM
To: [hidden email]
Subject: Re: [Elecraft] K3/K3s filter setting with the K3 Utility

Earlier I gave an example of a situation where you might choose to enable a
roofing filter at a bandwidth wider than the bandwidth marked on the filter.
I also gave a poor example of enabling a filter at a narrower bandwidth.
Here is a better one:

You use a variety of digital modes with different bandwidths, one of which
happens to be the same as or close to the bandwidth of one of your roofing
filters. You find that when that roofing filter is engaged, that particular
digital mode does not decode as well as it does with a wider filter setting.
You might find that changing the configuration to switch that filter in at a
narrower setting allows that particular mode to decode well, without having
a noticeable adverse effect on the next narrower bandwidth mode you normally
use. The likelihood of all this happening in combination with an actual need
for a tight roofing filter because of nearby very strong signals might be
quite low, but there is at least a theoretical possibility of such a
scenario. There are probably more likely situations - just pointing out that
it is not impossible that someone might want to do this. The good thing is,
the capability is there if you somehow find that you need it.

73,
Rich VE3KI
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[Gary Smith-2]

Rich,

Interesting food for thought. I just
received my 1.8 for the sub RX and was
wondering what others found most helpful
seeing as there are the options to custom
tailor the settings. At the same time, I
really make great use of the narrow filter
on CW and am always looking for something
I can do with what I have that is better
than I have been doing.

Thanks for your reply.

73,

Gary
KA1J

> There can be reasons to configure a roofing filter differently from
> its nominal bandwidth.
>
> For example, I have a "250 Hz" filter. According to the filter plots
> on the Elecraft web site, the 6 dB bandwidth of this filter is
> actually closer to 375 Hz. I configured my filter to switch in at 350
> Hz, which makes it much more useful to me than it would be if I had
> configured it to switch in at 250 Hz.
>
> If this filter is configured to switch in at 250 Hz in agreement with
> the label, then when you set your DSP bandwidth to 300 Hz or 350 Hz,
> you will be using the next wider filter in your receiver. Strong
> signals outside the DSP bandwidth but inside the wider  roofing
> filter's bandwidth can still have bad effects, whereas if the filter
> is configured to switch in at 350 Hz, you can take advantage of its
> ability to reduce those unwanted signals with relatively minor impact
> on signals within the DSP bandwidth.
>
> Of course, if the bandwidth of the 250 Hz filter really was 250 Hz,
> configuring it to switch in at 350 Hz would render the 300 Hz and 350
> Hz settings of the DSP filter somewhat less useful, since the actual
> bandwidth of the filter combination would now be close to 250 Hz
> regardless of what the DSP control said.
>
> There might be reasons to go in the other direction as well, i.e. to
> configure a filter to switch in only at a narrower bandwidth than the
> bandwidth marked on the filter. For example, if you had 500 Hz and
> 1000 Hz filters and often used a digital mode whose bandwidth was,
> say, 750 Hz, you could configure the 1000 Hz roofing filter to switch
> in only at 700 Hz and below. This would give you better filtering
> between 500 Hz and 700 Hz than without the 1000 Hz filter, while still
> permitting the 750 Hz mode signals to pass through at DSP settings of
> 750 Hz and above without being restricted by the roofing filter.
>
> 73,
> Rich VE3KI
>
>
> KA1J wrote:
>
> Is there any advantage to setting the 1.8
> above, say as 2. in the utility.
>
> Or to have the 200Hz filter engaged at say
> 250?
> ______________________________________________________________
> 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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