CW Filter and Roofing Filter

[rclark01]

Hi all:
I currently own a Yaesu FT-950 and am considering selling it to move the the Elecraft K3S line. My question is about filters. My FT-950 has a roofing filter and a variable CW filter down to 200hz. Quite frankly, I can't tell much different when I switch in the roofing filter but the variable CW filter makes a big difference. I also have a 1970's TenTen Century 21 which has a 500Hz filter that, to me, seems to do a better job than the FT-950. So..when I read that a 500 Hz roofing filter is an option for the Elecraft K3S, what am I actually reading? Could there be a 500Hz roofing filter and a 500Hz CW filter or are they the same? In several Youtube videos, I've seen operators using the variable width the filter signals. What am I seeing? Are they adjusting the roofing filter or the cw filter? And...is the cw filter variable (like my FT-950) or fixed (like the Century 21)?
Thanks!

Robert NJ4j
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[wayne burdick]

Hi Robert,

For best overall performance in CW mode with the K3S, I suggest using our 400-Hz 8-pole filter. The 250-Hz 8-pole filter is a further optimization, with very steep skirts to help with close-in QRM. 5-pole filters are also available but they won't have as steep skirts. (The 500-Hz 5-pole is not appreciably wider than the 400-Hz 8-pole.)

With either filter selected, high-performance, variable-bandwidth DSP filtering is applied within the crystal filter passband. As you adjust the bandpass controls, the K3S will automatically select the right crystal filter. The DSP filtering can go to as narrow as 50 Hz, and as wide as the widest crystal filter installed that is compatible with CW mode (up to 2.8 kHz, another one of our 8-pole filters.)

In addition, the DSP also provides a switchable audio peaking filter in CW mode (APF). This is a special filter type that can make signals very close to noise floor seem to emerge from the noise ("magically," some have said), without adding the ringing associated with traditional "brick-wall" filters.

Other weapons in the K3S's weak-signal arsenal include CW REVerse mode, DSP and IF noise blankers, noise reduction, and both auto- and manual notch.

73,
Wayne
N6KR



On Jun 23, 2015, at 11:42 AM, [hidden email] wrote:

> Hi all:
> I currently own a Yaesu FT-950 and am considering selling it to move the the Elecraft K3S line. My question is about filters. My FT-950 has a roofing filter and a variable CW filter down to 200hz. Quite frankly, I can't tell much different when I switch in the roofing filter but the variable CW filter makes a big difference. I also have a 1970's TenTen Century 21 which has a 500Hz filter that, to me, seems to do a better job than the FT-950. So..when I read that a 500 Hz roofing filter is an option for the Elecraft K3S, what am I actually reading? Could there be a 500Hz roofing filter and a 500Hz CW filter or are they the same? In several Youtube videos, I've seen operators using the variable width the filter signals. What am I seeing? Are they adjusting the roofing filter or the cw filter? And...is the cw filter variable (like my FT-950) or fixed (like the Century 21)?
> Thanks!
>
> Robert NJ4j
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[Guy Olinger K2AV]

Hi Robert,

K3(S) operators often set the DSP bandwidth to the roofing filter width
having bought the filter with operating at that bandwidth in mind. However
the DSP bandwidth is variable. As this is varied the radio will use the
roofer equal to or next larger than the DSP bandwidth.

Operating a K3(S) roofing filter and DSP with coinciding skirts produces
exceptional quick rejection of close interference, which is very useful
"running" in a contest, particularly on CW.

Hope this helps.

73, Guy K2AV

On Tuesday, June 23, 2015, <[hidden email]> wrote:

> Hi all:
> I currently own a Yaesu FT-950 and am considering selling it to move the
> the Elecraft K3S line. My question is about filters. My FT-950 has a
> roofing filter and a variable CW filter down to 200hz. Quite frankly, I
> can't tell much different when I switch in the roofing filter but the
> variable CW filter makes a big difference. I also have a 1970's TenTen
> Century 21 which has a 500Hz filter that, to me, seems to do a better job
> than the FT-950. So..when I read that a 500 Hz roofing filter is an option
> for the Elecraft K3S, what am I actually reading? Could there be a 500Hz
> roofing filter and a 500Hz CW filter or are they the same? In several
> Youtube videos, I've seen operators using the variable width the filter
> signals. What am I seeing? Are they adjusting the roofing filter or the cw
> filter? And...is the cw filter variable (like my FT-950) or fixed (like the
> Century 21)?
> Thanks!
>
> Robert NJ4j
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email] <javascript:;>
>
> 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] <javascript:;>
>

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[Don Wilhelm-4]

Robert,

Actually there is no good comparison with either your Yaesu or the TenTec.
The DSP sets the ultimate signal bandwidth and is continuously variable
from greater than 2.8kHz down to 50 Hz.  There is no specific CW
filter.  Adjust for a width that is appropriate for your mode, band
conditions and your personal choice of a good filter width.

That leaves the question of the roofing filter(s) unanswered.  The K3
(or K3S) will work with only the stock 2.7kHz or the 8 pole 2.8kHz
filter - you must have one or the other in the K3.
Other roofing filters may be desirable in your K3 when you are working
in crowded band conditions where there may be strong nearby signals that
are outside your DSP filter, yet are within the passband of the roofing
filter - in other words, you may not hear them.  Those strong signals
will activate the hardware AGC (which is there mainly to protect the A
to D converter from overload).  If those signals activate the Hdwr AGC,
you will hear "AGC Pumping" in the receiver and the receiver sensitivity
will be reduced when that strong signal transmits.
The cure for the effects above is to add narrow roofing filters to
reduce the K3 response to those nearby strong signals.  The roofing
filters are automatically switched in as you narrow the DSP filter
bandwidth.

73,
Don W3FPR

On 6/23/2015 2:42 PM, [hidden email] wrote:
> Hi all:
> I currently own a Yaesu FT-950 and am considering selling it to move the the Elecraft K3S line. My question is about filters. My FT-950 has a roofing filter and a variable CW filter down to 200hz. Quite frankly, I can't tell much different when I switch in the roofing filter but the variable CW filter makes a big difference. I also have a 1970's TenTen Century 21 which has a 500Hz filter that, to me, seems to do a better job than the FT-950. So..when I read that a 500 Hz roofing filter is an option for the Elecraft K3S, what am I actually reading? Could there be a 500Hz roofing filter and a 500Hz CW filter or are they the same? In several Youtube videos, I've seen operators using the variable width the filter signals. What am I seeing? Are they adjusting the roofing filter or the cw filter? And...is the cw filter variable (like my FT-950) or fixed (like the Century 21)?
>

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[k6dgw]

Robert, I don't think you can make the comparison as you suggest, very
different radios.  I don't remember when the term "roofing filter"
entered the ham vocabulary but it has caused a lot of confusion, some
angst, and possibly some over-buying of filters.

In the K3 and K3S, the bandwidth that you actually hear in your
headphones or speaker is set by the DSP with the WIDTH knob.  It's
essentially a brick-wall filter, built with binary arithmetic.  If the
signal is not inside the passband, you don't hear it.

Our bands are full of signals, some very strong which will activate the
hardware AGC and reduce the level of *all* signals at the input to the
ADC ... including the one weak one you're listening to.  All the roofing
filter does is restrict the BW of the energy applied to the ADC to
exclude most of the other signals on the band.  I'm not at all surprised
that you don't notice much effect from the 1st IF filter, you won't
unless there are very strong signals that will activate the AGC.

Matching the roofer BW and DSP BW offers a small benefit since two
filters are cascaded.  But, since the roofers are not adjustable, you
have to find a happy compromise for your operating style.  My K3 came
with a 2.7 KHz 5-pole filter for SSB and I added a 500 Hz for CW.
That's all I have.  I contest some [not anywhere near hard core], nearly
all CW, and I operate casually, nearly always at 250 or 200 Hz DSP BW.
For SSB, I usually run the DSP BW at 2.1 KHz, that's what the Collins
mech filter was in my S-Line and I'm used to the sound.  I've never
noticed a strong signal, outside the DSP BW but inside the roofer
activate the K3's hardware AGC.  Now, you asked questions ...

"When I read that a 500 Hz roofing filter is an option for the Elecraft
K3S, what am I actually reading?"

Elecraft offers a 500 Hz filter [and maybe a 250 Hz] for narrow-band
modes which will restrict the BW of the energy presented to the ADC.  If
you operate CW or other narrow-band modes a lot, I think it's a good
buy.  If you're mainly a phone guy, you might not ever encounter a
situation where it would make a difference.  I think the filters are
really Inrads, I had a 250 Hz Inrad in a TS-850, and it was pretty "ringey."

"Could there be a 500Hz roofing filter and a 500Hz CW filter
or are they the same?"

K3?  If so, no, they are not the same if "500Hz CW filter" means what
you set in the DSP.  You can have a 500 Hz roofer, I do.  You can set
the DSP BW on CW to 500 Hz [you can set it much wider than that in
fact].  The K3 will select the 500 Hz roofer, and you'll have two
cascaded filters.  Keep in mind, the roofers are analog crystal filters,
not adjustable.   They are nominally xxxx Hz wide, but the skirts are
not vertical.

"In several Youtube videos, I've seen operators using the variable width
the filter signals. What am I seeing?"

If they're using a K3, they're adjusting the DSP WIDTH control.

"is the cw filter variable (like my FT-950) or fixed (like the Century 21)?"

There is no "CW" filter in a K3/K3S.  There is a roofing filter that
restricts the BW going into the ADC, and there is a DSP filter
controlled by knobs on the front panel which can be set to anything
within its range, regardless of operating mode.  The roofer isn't
adjustable.  The knobs do the same thing whether your listening to CW,
RTTY, PSK31, SSB, or anything else.

Small exception to the above:  Separate from the roofing and DSP
filters, the K3/K3S has a switchable [on/off] audio peaking filter for
CW.  It too is done in binary arithmetic, is totally separate and only
good for CW, and under some conditions it can render an unreadable
signal quite readable.

Hope this helps,

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 50th Running of the Cal QSO Party 3-4 Oct 2015
- www.cqp.org

> On 6/23/2015 2:42 PM, [hidden email] wrote:
>> Hi all:
>> I currently own a Yaesu FT-950 and am considering selling it to move
>> the the Elecraft K3S line. My question is about filters. My FT-950 has
>> a roofing filter and a variable CW filter down to 200hz. Quite
>> frankly, I can't tell much different when I switch in the roofing
>> filter but the variable CW filter makes a big difference. I also have
>> a 1970's TenTen Century 21 which has a 500Hz filter that, to me, seems
>> to do a better job than the FT-950. So..when I read that a 500 Hz
>> roofing filter is an option for the Elecraft K3S, what am I actually
>> reading? Could there be a 500Hz roofing filter and a 500Hz CW filter
>> or are they the same? In several Youtube videos, I've seen operators
>> using the variable width the filter signals. What am I seeing? Are
>> they adjusting the roofing filter or the cw filter? And...is the cw
>> filter variable (like my FT-950) or fixed (like the Century 21)?

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