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K3: roofing filter configuration settings

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K3: roofing filter configuration settings

A question regarding roofing filter "configuration bandwidth" settings on
the K3:

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?

Likewise, the 400hz roofer has a BW6 of 450hz, so perhaps for certain modes
a "configuration bandwidth" setting of 450 rather than 400 could be
beneficial as well?

If anyone is wondering where I'm getting the term "configuration bandwidth"
from, it's a configuration heading on the K3 Utility programs filter
configuration page.

Thanks & 73,

Dick- K9OM

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Arie Kleingeld PA3A-2

Re: K3: roofing filter configuration settings

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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Bob McGraw - K4TAX

Re: K3: roofing filter configuration settings

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
>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]
>

Guy Olinger K2AV

Re: K3: roofing filter configuration settings

What the K3 contesters around here have done with the "400" and "250"
roofing filters is assign them 450 and 350. For someone running in a
contest, those are meaningful settings where is is *desired* to have the
DSP and roofing skirts concurrent for sharp adjacent channel rejection.

As to where those numbers came from they are the exact same filter
(different mounting) as the INRAD 8 MHz 400 and 250 Filters for the Yaesu
MP series. Those are part of a *cascade pair* with a 455 kHz IF filter that
give razor sharp performance at 400 and 250 bandwidth, where the pairs
really are 400 and 250. In the MP you put the "400" filters in the 500
slots. The MP skirts are still going down at -100 dB. I've never been able
to measure the bottom.

In any event, E's use of the 8 MHz as a roofing filter makes perfect sense.
When needing very narrow settings, the DSP skirts inside the 350 roofer's
skirts works well enough for me so far.

73, Guy K2AV

On Wed, Feb 10, 2016 at 8:32 AM, Bob McGraw K4TAX <[hidden email]>
wrote:

> 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
>>>
>>
>> ______________________________________________________________
>> 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
>> Message delivered to [hidden email]
>>
>>
>
> ______________________________________________________________
> Elecraft mailing list
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>

john@kk9a.com

Re: K3: roofing filter configuration settings

In reply to this post by Elecraft mailing list

This sounds like a great idea. I used Inrad 250Hz filters in my Yaesu
FT1000MP Mark-V and they worked great on RTTY but I found the 250Hz
setting to be too narrow on my K3S. Is anyone doing this?

John KK9A

RLVZ at aol.com RLVZ at aol.com
Wed Feb 10 00:05:30 EST 2016

A question regarding roofing filter "configuration bandwidth" settings on
the K3:

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?

Likewise, the 400hz roofer has a BW6 of 450hz, so perhaps for certain modes
a "configuration bandwidth" setting of 450 rather than 400 could be
beneficial as well?

If anyone is wondering where I'm getting the term "configuration bandwidth"
from, it's a configuration heading on the K3 Utility programs filter
configuration page.

Thanks & 73,

Dick- K9OM

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Joe Subich, W4TV-4

Re: K3: roofing filter configuration settings

On 2/10/2016 11:12 AM, [hidden email] wrote:
> This sounds like a great idea. I used Inrad 250Hz filters in my Yaesu
> FT1000MP Mark-V and they worked great on RTTY but I found the 250Hz
> setting to be too narrow on my K3S.

The INRAD filters are spec'd for -3dB bandwidth. This goes way back to
the original "International Radio" as a spin off of the Fox Tango club.
Yaesu (and Kenwood) specified their filters for operational bandwidth -
with two filters (1st and 2nd IF) in cascade. Thus 250 Hz at - 3dB in
each filter/IF resulted in an overall 250 Hz at -6dB for the two in
cascade.

A *single* 250 Hz filter - typically the 1st IF - was a very good RTTY
filter since it had a 370 - 400 Hz bandwidth and relatively low group
delay (phase distortion) at the "corners".

Unfortunately, that doesn't quite work with the K3 where the DSP is set
to 250 Hz because the DSP has very sharp skirts (high levels of phase
distortion). However, it will work if the "250 Hz" filter is set to
kick in at 390 Hz in RTTY and the DSP is also set for 390 Hz. You
achieve a very sharp 390 Hz bandwidth (the DSP "cleans up" the skirts
of the IF filter) with minimum required bandwidth for 45 baud 170 Hz
shift RTTY.

Going back to the original question in this thread ... setting the 400
Hz filter as a 450 Hz and the 250 Hz filter as a 370 Hz filter results
in the sharpest skirts with overall bandwidth (at - 6dB) roughly the
same as the 450/370 settings. That may not be enough difference to
justify the cost (price and "slot") of both IF filters and is one reason
I prefer the "400 Hz" along with the Elecraft 200 Hz - 5 pole filter
when it is available. I don't see enough improvement with the "250 Hz"
filter in RTTY to justify both.

73,

... Joe, W4TV

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Ed Muns

Re: K3: roofing filter configuration settings

In reply to this post by Elecraft mailing list

"Configuration bandwidth" is the DSP bandwidth at which the given crystal
filter engages in the K3/K3S. This crystal filter remains engaged as the
DSP bandwidth is narrowed, to the point where another crystal filter's
"configuration bandwidth" is reached.

In choosing the configuration bandwidth, one consideration is the cascade
effect of the crystal and DSP filter bandwidths. In general, the cascade
bandwidth will be less than either of these two filter bandwidths. The
extent to which this is true depends on how close the two filter bandwidths
are to one another.

This reduced cascade bandwidth is the underlying reason for the KFL3A-250
crystal filter from INRAD being called "250 Hz" but actually measuring about
370 Hz at -6 dB and about 310 Hz at -3 dB. (See
http://www.elecraft.com/K3/K3_filter_plots.htm.) This filter was originally
designed for the Yaesu first IF and intended to be used in conjunction with
another "250 Hz" filter in the second IF. Each filter is actually wider
than its marketing name because when the two are cascaded, the resulting
bandwidth is about 250 Hz.

The cascade effect of the K3 crystal and DSP IF filters is less than the
Yaesu and Kenwood cases where both filters were crystal filters, each with a
somewhat "round" shape. The K3 DSP filter is more "square" in the
transition between passband and stopband.

Since the K3 DSP bandwidth is continuously variable, it becomes more
important to consider this cascade effect because it may or may not be
significant depending on how close the crystal and DSP filter bandwidths are
to one another. It is also more important with the K3 to be aware of the
actual crystal filter bandwidths.

For RTTY operation, the minimum cascaded bandwidth should be about 400 Hz.
This is because modern software decoders, e.g., MMTTY and 2Tone, use
algorithms that make use of the sidebands of each tone in order to minimize
error rate. Using narrower IF filters, including the DTF, in the radio
attenuates these useful sidebands.

For the same reason, the K3 (and, Icom) dual-tone filter removes sideband
information that could be used by the decoder to improve copy. Anecdotally,
in pileup and QRM situations such as DXpeditions and contests, I've found a
cascaded IF bandwidth of 400-500 Hz to be superior to the narrower
bandwidths, including the DTF, that I used several years ago.

Accordingly, I've chosen the INRAD 500 Hz 8-pole filter for CW and RTTY,
setting my DSP bandwidth to 400-500 Hz as desired. I think this gives
marginally better, and more versatile, filtering than the KFL3A-250.

For very heavy QRM CW situations, e.g., 160 meter contests, the 5-pole 200
Hz crystal filter is useful.

Ed W0YK
____________________________________________________________________________
___

Dick K9OM wrote:

A question regarding roofing filter "configuration bandwidth" settings on
the K3:

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?

Likewise, the 400hz roofer has a BW6 of 450hz, so perhaps for certain modes
a "configuration bandwidth" setting of 450 rather than 400 could be
beneficial as well?

If anyone is wondering where I'm getting the term "configuration bandwidth"
from, it's a configuration heading on the K3 Utility programs filter
configuration page.

______________________________________________________________
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