Re: [Elecraft] [K3] Roofing Filter Question

[Joe Subich, W4TV]

If one sets a DSP bandwidth greater than the wisest installed roofing
filter the bandwidth will be determined strictly by the characteristics
of the roofing filter and the lowpass filter (4.2 KHz) in the audio
chain.

73,

   ... Joe, W4TV

On 6/30/2016 10:10 AM, rick jones via Elecraft wrote:

I understand that the DSP is after the roofing filters but I don't understand 
why one can dial in a bandwidth wider then the installed roofing filter. When I 
do so, am I hearing the skirts of the filter and the attenuated signals outside 
of the filter's passband as well? Thank you.
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[Elecraft] [K3] Roofing Filter Question

[rick jones via Elecraft]

I understand that the DSP is after the roofing filters but I don't understand 
why one can dial in a bandwidth wider then the installed roofing filter. When I 
do so, am I hearing the skirts of the filter and the attenuated signals outside 
of the filter's passband as well? Thank you.  
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Re: [Elecraft] K3: roofing filter configuration settings

[Ed Muns]

"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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Re: [Elecraft] K3: roofing filter configuration settings

[Bob McGraw K4TAX]

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. Sowhat 
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?
  

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Re: [Elecraft] K3: roofing filter configuration settings

[Guy Olinger K2AV]

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 
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. Sowhat 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?
>>>   >>   Dick- K9OM
>>>
>>
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>
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Re: [Elecraft] K3: roofing filter configuration settings

[j...@kk9a.com]

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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Re: [Elecraft] K3: roofing filter configuration settings

[Arie Kleingeld PA3A]

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?
  
  
Dick- K9OM
  


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Re: [Elecraft] K3: roofing filter configuration settings

[Joe Subich, W4TV]

On 2/10/2016 11:12 AM, j...@kk9a.com 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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[Elecraft] K3: roofing filter configuration settings

[Dick via Elecraft]

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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[Elecraft] K3: Roofing Filter

[John Reilly]

Has the 200 Hz, 5-pole roofing filter (KFL3A-200) been discontinued?
Thanks,
  - 73, John, N0TA
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Re: [Elecraft] K3: Roofing Filter

[Wayne Burdick]

As I mentioned earlier, we're considering various alternatives.

73,
Wayne
N6KR


On Sep 25, 2015, at 3:20 PM, Kevin Stover  wrote:

> Yep.
> INRAD isn't making/selling  them anymore either so 250Hz is as tight as you 
> can go until/if Elecraft comes up with a suitable replacement. I'm not 
> holding my breath.
> 
> 
> On 9/25/2015 3:28 PM, John Reilly wrote:
>> Has the 200 Hz, 5-pole roofing filter (KFL3A-200) been discontinued?
>> Thanks,
>>  - 73, John, N0TA
>> _


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Re: [Elecraft] K3: Roofing Filter

[Kevin Stover]

Yep.
INRAD isn't making/selling  them anymore either so 250Hz is as tight as 
you can go until/if Elecraft comes up with a suitable replacement. I'm 
not holding my breath.



On 9/25/2015 3:28 PM, John Reilly wrote:

Has the 200 Hz, 5-pole roofing filter (KFL3A-200) been discontinued?
Thanks,
  - 73, John, N0TA
_



--
R. Kevin Stover
AC0H
ARRL
FISTS #11993
SKCC #215
NAQCC #3441

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Re: [Elecraft] K3: Roofing Filter

[Jerry Moore]

I just purchased my K3s and had gotten the 400hz 8 pole from the reflector
here. I've been very happy to find the DSP filtering goes down to what
appears to be 50hz and works VERY WELL so far for me. Of course I've not
been under CW contest type conditions but haven't had any issues filtering
between two close signals. 
Just sharing my experiences as a new owner.



Jerry Moore
AE4PB, K3S - S.N. 010324
An Amatuer is - Considerate, Loyal, Progressive, Friendly, Balanced, and
Patriotic.



-Original Message-
From: Elecraft [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Wayne
Burdick
Sent: Friday, September 25, 2015 7:06 PM
To: Kevin Stover
Cc: elecraft@mailman.qth.net
Subject: Re: [Elecraft] K3: Roofing Filter

As I mentioned earlier, we're considering various alternatives.

73,
Wayne
N6KR


On Sep 25, 2015, at 3:20 PM, Kevin Stover <kevin.sto...@mediacombb.net>
wrote:

> Yep.
> INRAD isn't making/selling  them anymore either so 250Hz is as tight as
you can go until/if Elecraft comes up with a suitable replacement. I'm not
holding my breath.
> 
> 
> On 9/25/2015 3:28 PM, John Reilly wrote:
>> Has the 200 Hz, 5-pole roofing filter (KFL3A-200) been discontinued?
>> Thanks,
>>  - 73, John, N0TA
>> _


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delivered to je...@carolinaheli.com

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[Elecraft] K3 Roofing filter--KFL3A-2.1k

[Steve]

Hi agn,  My buyer of the KFL3A-2.1k filter backed 
out, so it's available for $125.00 shipped to ur qth.
Tnx es vy 73'
Steve W8CRH
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Re: [Elecraft] K3 Roofing Filter Gain Setup

[drewko]

If I use a 50uv signal generator to set the filter gains for equal
readings on my K3's AFV meter I arrive at the following compensations:

2.70 KHz = 0db
500 Hz = 4 db
250 Hz = 8 db

This is way more aggressive than the suggested amounts but these
figures do sound equalized to my ears for real signal conditions. The
factory settings are noticeably weak. Maybe my particular filters are
just not up to par.

73,
Drew
AF2Z


On Sat, 28 May 2011 14:18:45 -0700, you wrote:

There are recommendations in the K3 Owner's manual (see Crystal Filter
Setup, indexed, on page 46) :

Use VFO A to set the gain in dB. In general, you'll want to add 1-2 dB for
400-500 Hz filters, and 3-4 dB for 200-250 Hz filters. 

and there is a table (with essentially the same guidance) in K3 Utility Help
for the Filter Configuration page. I've lost the table formatting in
cut/paste from Help, but here's the information:

Narrow crystal filters tend to have more passband loss than wide filters.
You can compensate for this effect by specifying an amount of added gain to
use for each filter in receive mode. Enter the desired gain boost, in
decibels, for each filter. You may specify a value between 0 and 8 dB. 

Elecraft recommends using the initial loss compensation values below. You
may wish to further adjust the values for your particular filters. 

Part Number Bandwidth Gain 

KFL3A-200 0.20 kHz 3-4 dB 
KFL3A-250 0.25 kHz 3-4 dB 
KFL3A-400 0.40 kHz 1-2 dB 
KFL3A-500 0.50 kHz 1-2 dB 
KFL3A-1.0K 1.00 kHz 0 dB 
KFL3A-1.8K 1.80 kHz 0 dB 
KFL3A-2.1K 2.10 kHz 0 dB 
KFL3A-2.7K 2.70 kHz 0 dB 
KFL3A-2.8K 2.80 kHz 0 dB 
KFL3A-6K 6.00 kHz 0 dB 
KFL3B-FM 13.00 kHz 0 dB

73 de Dick, K6KR



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Re: [Elecraft] K3 Roofing Filter Gain Setup

[Brian Alsop]

On 5/29/2011 13:43, drewko wrote:
 If I use a 50uv signal generator to set the filter gains for equal
 readings on my K3's AFV meter I arrive at the following compensations:

 2.70 KHz = 0db
 500 Hz = 4 db
 250 Hz = 8 db

 This is way more aggressive than the suggested amounts but these
 figures do sound equalized to my ears for real signal conditions. The
 factory settings are noticeably weak. Maybe my particular filters are
 just not up to par.

 73,
 Drew
 AF2Z


 On Sat, 28 May 2011 14:18:45 -0700, you wrote:

 There are recommendations in the K3 Owner's manual (see Crystal Filter
 Setup, indexed, on page 46) :

 Use VFO A to set the gain in dB. In general, you'll want to add 1-2 dB for
 400-500 Hz filters, and 3-4 dB for 200-250 Hz filters.

 and there is a table (with essentially the same guidance) in K3 Utility Help
 for the Filter Configuration page. I've lost the table formatting in
 cut/paste from Help, but here's the information:

 Narrow crystal filters tend to have more passband loss than wide filters.
 You can compensate for this effect by specifying an amount of added gain to
 use for each filter in receive mode. Enter the desired gain boost, in
 decibels, for each filter. You may specify a value between 0 and 8 dB.

 Elecraft recommends using the initial loss compensation values below. You
 may wish to further adjust the values for your particular filters.

 Part Number Bandwidth Gain

 KFL3A-200 0.20 kHz 3-4 dB
 KFL3A-250 0.25 kHz 3-4 dB
 KFL3A-400 0.40 kHz 1-2 dB
 KFL3A-500 0.50 kHz 1-2 dB
 KFL3A-1.0K 1.00 kHz 0 dB
 KFL3A-1.8K 1.80 kHz 0 dB
 KFL3A-2.1K 2.10 kHz 0 dB
 KFL3A-2.7K 2.70 kHz 0 dB
 KFL3A-2.8K 2.80 kHz 0 dB
 KFL3A-6K 6.00 kHz 0 dB
 KFL3B-FM 13.00 kHz 0 dB

 73 de Dick, K6KR



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Re: [Elecraft] K3 Roofing Filter Gain Setup

[Brian Alsop]

On 5/29/2011 13:43, drewko wrote:
 If I use a 50uv signal generator to set the filter gains for equal
 readings on my K3's AFV meter I arrive at the following compensations:

 2.70 KHz = 0db
 500 Hz = 4 db
 250 Hz = 8 db

 This is way more aggressive than the suggested amounts but these
 figures do sound equalized to my ears for real signal conditions. The
 factory settings are noticeably weak. Maybe my particular filters are
 just not up to par.

 73,
 Drew
 AF2Z


 On Sat, 28 May 2011 14:18:45 -0700, you wrote:

 There are recommendations in the K3 Owner's manual (see Crystal Filter
 Setup, indexed, on page 46) :

 Use VFO A to set the gain in dB. In general, you'll want to add 1-2 dB for
 400-500 Hz filters, and 3-4 dB for 200-250 Hz filters.

 and there is a table (with essentially the same guidance) in K3 Utility Help
 for the Filter Configuration page. I've lost the table formatting in
 cut/paste from Help, but here's the information:

 Narrow crystal filters tend to have more passband loss than wide filters.
 You can compensate for this effect by specifying an amount of added gain to
 use for each filter in receive mode. Enter the desired gain boost, in
 decibels, for each filter. You may specify a value between 0 and 8 dB.

 Elecraft recommends using the initial loss compensation values below. You
 may wish to further adjust the values for your particular filters.

 Part Number Bandwidth Gain

 KFL3A-200 0.20 kHz 3-4 dB
 KFL3A-250 0.25 kHz 3-4 dB
 KFL3A-400 0.40 kHz 1-2 dB
 KFL3A-500 0.50 kHz 1-2 dB
 KFL3A-1.0K 1.00 kHz 0 dB
 KFL3A-1.8K 1.80 kHz 0 dB
 KFL3A-2.1K 2.10 kHz 0 dB
 KFL3A-2.7K 2.70 kHz 0 dB
 KFL3A-2.8K 2.80 kHz 0 dB
 KFL3A-6K 6.00 kHz 0 dB
 KFL3B-FM 13.00 kHz 0 dB

 73 de Dick, K6KR



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Re: [Elecraft] K3 Roofing Filter Gain Setup

[Brian Alsop]

Sorry guys, having trouble with email program today. Please ignore 
multiple messages.

Drew,

Interesting.

Did the same with a signal generator, S3 signal, AGC off and Spectrogram 
to match the peak.  I'm primarily interested in weak signal CW work and 
don't want to fool with the AF gain when filter settings changed.

My results:
2.7 0 db
1.8 2
400 5
250 8
200 8

Have others say they didn't think 8db gain was enough for the narrowest 
filters.  The only way I can see to get 4db for the narrowest filters is 
to somehow set a negative value for the 2.7 filter.  That might not be 
all that bad to have such a capability.

I wish somebody would explain excatly what the RF gain calibration does 
and how it works. This is typically done after the crystal filter gains 
are set.  The procedure asks one to set the filter width to 100 Hz. 
That of course would kick in the 200 Hz filter here.  But some have said 
this procedure sets the gain of the stage before the filters.  So why 
specify a filter width setting?  What is monitored during the RF gain 
adjustment process?

73 de Brian/K3KO


On 5/29/2011 14:02, Brian Alsop wrote:
 On 5/29/2011 13:43, drewko wrote:
 If I use a 50uv signal generator to set the filter gains for equal
 readings on my K3's AFV meter I arrive at the following compensations:

 2.70 KHz = 0db
 500 Hz = 4 db
 250 Hz = 8 db

 This is way more aggressive than the suggested amounts but these
 figures do sound equalized to my ears for real signal conditions. The
 factory settings are noticeably weak. Maybe my particular filters are
 just not up to par.

 73,
 Drew
 AF2Z


 On Sat, 28 May 2011 14:18:45 -0700, you wrote:

 There are recommendations in the K3 Owner's manual (see Crystal Filter
 Setup, indexed, on page 46) :

 Use VFO A to set the gain in dB. In general, you'll want to add 1-2 dB for
 400-500 Hz filters, and 3-4 dB for 200-250 Hz filters.

 and there is a table (with essentially the same guidance) in K3 Utility Help
 for the Filter Configuration page. I've lost the table formatting in
 cut/paste from Help, but here's the information:

 Narrow crystal filters tend to have more passband loss than wide filters.
 You can compensate for this effect by specifying an amount of added gain to
 use for each filter in receive mode. Enter the desired gain boost, in
 decibels, for each filter. You may specify a value between 0 and 8 dB.

 Elecraft recommends using the initial loss compensation values below. You
 may wish to further adjust the values for your particular filters.

 Part Number Bandwidth Gain

 KFL3A-200 0.20 kHz 3-4 dB
 KFL3A-250 0.25 kHz 3-4 dB
 KFL3A-400 0.40 kHz 1-2 dB
 KFL3A-500 0.50 kHz 1-2 dB
 KFL3A-1.0K 1.00 kHz 0 dB
 KFL3A-1.8K 1.80 kHz 0 dB
 KFL3A-2.1K 2.10 kHz 0 dB
 KFL3A-2.7K 2.70 kHz 0 dB
 KFL3A-2.8K 2.80 kHz 0 dB
 KFL3A-6K 6.00 kHz 0 dB
 KFL3B-FM 13.00 kHz 0 dB

 73 de Dick, K6KR



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Re: [Elecraft] K3 Roofing Filter Gain Setup

[Lyle Johnson]

RF Gain Calibration  measures the effect of the hardware AGC voltage on 
the K3's receive gain, in dB.

It uses a narrow filter setting to improve the S/N of the signal 
measured by the DSP as the gain decreases and the signal being measured 
is reduced in amplitude due to that decrease.

The hardware AGC voltage is applied after the 8.215 MHz roofing filters, 
so the accuracy of the filter gain compensation is of no practical 
consequence as long as the roofing filter selection is not changed 
during the calibration process.

Becasue the hardware AGC calibration may affect the reported S Meter 
values, S Meter calbration should be checked and adjusted if required, 
after RF Gain Calibration is completed.

73,

Lyle KK7P

 I wish somebody would explain excatly what the RF gain calibration does
 and how it works. This is typically done after the crystal filter gains
 are set.  The procedure asks one to set the filter width to 100 Hz.
 That of course would kick in the 200 Hz filter here.  But some have said
 this procedure sets the gain of the stage before the filters.  So why
 specify a filter width setting?  What is monitored during the RF gain
 adjustment process?

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[Elecraft] K3 Roofing Filter Gain Setup

[goldtr8]

Gents,

I am searching without much luck for recommendations for the gain 
setting recommendations for roofing filters.

Specfically I have a 700 hz 8 pole and a 200 hz filter 5 pole.   There 
is a gain setting in the k3 setup menue and I remember there were 
recomendations on how to choose this setting.  However, I have not been 
able to find reference on the net.

Please can anyone provide some guidance as the performance when these 
filters are engaged with digital modes is rather disapointing.What I 
mean by this is that a signal can be very clean with the 2.7 or 2.1 
filter engaged but if  I use on of these filters the signal becomes very 
poor.  I want to use these to isolate close in signals but there appears 
to be a lot of distortation so they are basically of little use.

I am betting that there is more to this gain setting than meets the eye 
and that is where my problem is.  I have put the gain for these two 
filters at 1 and the 2.1  2.7 at zero.

I will be playing around with the settings, but there is a method to set 
this parameter so I need to learn what and why so I can make them work 
the way they are supposed to work.

Thanks and have a great holiday.

Don
KD8NNU
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Re: [Elecraft] K3 Roofing Filter Gain Setup

[Matt Zilmer]

From D9 Owner's Manual (may be downrev at this point), p49:

Use VFO A to set the gain in dB. In general,
you’ll want to add 1-2 dB for 400-500 Hz
filters, and 3-4 dB for 200-250 Hz filters.

I left the 1.8, 2.8, 6 and 13K filters alone.  The 250 Hz I have set
for 3 dB gain.

matt W6NIA

--
On Sat, 28 May 2011 15:17:23 -0400 (EDT), you wrote:

Gents,

I am searching without much luck for recommendations for the gain 
setting recommendations for roofing filters.

Specfically I have a 700 hz 8 pole and a 200 hz filter 5 pole.   There 
is a gain setting in the k3 setup menue and I remember there were 
recomendations on how to choose this setting.  However, I have not been 
able to find reference on the net.

Please can anyone provide some guidance as the performance when these 
filters are engaged with digital modes is rather disapointing.What I 
mean by this is that a signal can be very clean with the 2.7 or 2.1 
filter engaged but if  I use on of these filters the signal becomes very 
poor.  I want to use these to isolate close in signals but there appears 
to be a lot of distortation so they are basically of little use.

I am betting that there is more to this gain setting than meets the eye 
and that is where my problem is.  I have put the gain for these two 
filters at 1 and the 2.1  2.7 at zero.

I will be playing around with the settings, but there is a method to set 
this parameter so I need to learn what and why so I can make them work 
the way they are supposed to work.

Thanks and have a great holiday.

Don
KD8NNU
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Re: [Elecraft] K3 Roofing Filter Gain Setup

[Gary Hvizdak]

Don (KD8NNU) writes ...

I am searching without much luck for recommendations for the gain 
setting recommendations for roofing filters.

=== = = = ===

Don,

See Wayne's K3 crystal filter offset/bandwidth/gain setting guidelines
post, dated 13 FEB 2009.  You will find it in the Reflector archives at
http://mailman.qth.net/pipermail/elecraft/2009-February/105445.html 

73,
Gary  KI4GGX



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Re: [Elecraft] K3 Roofing Filter Gain Setup

[goldtr8]

Dear All

I am looking at PSK31 signals not SSB and my definition of distortion is 
my visual observation on the PC waterfall in DM780 and the fact that 
decode of the signal by the PC starts to fail when I engage the narrow 
filters.   This is observed when I have clean signals using the 2.1 or 
2.7 filters and only DSP.  I do understand the how strong signals can 
create havoc in the band which is why I have the narrow filters.  The 
issue is until I get them setup to work well without interference I will 
not expect them to help much when I have close signals or weak signals 
that I want to pull out.

I do have all the offsets per the documentation with the filters so this 
should not be the issue.

Folks have pointed to some articles regarding the setting of the filter 
gain and have privided insight on how to use information on the K3 
display to help quantify signals.

My biggest problem is I have zero results when I do searches on these 
types of topics.  One of the responses was a link directly to a writeup 
that I had been searching for, go figure. :-)

All I know for sure is that again the user community has helped me get 
to the info I needed and now I have a basis of logic on what I will be 
looking at when I make some adjustments.

Now I need to get in front of the radio and follow the advice of the 
wise ones.

Thanks Everyone!!!


Don
KD8NNU


On Sat, May 28, 2011 at 3:17 PM, gold...@charter.net wrote:

 Gents,

 I am searching without much luck for recommendations for the gain 
 setting recommendations for roofing filters.

 Specfically I have a 700 hz 8 pole and a 200 hz filter 5 pole.   There 
 is a gain setting in the k3 setup menue and I remember there were 
 recomendations on how to choose this setting.  However, I have not 
 been able to find reference on the net.

 Please can anyone provide some guidance as the performance when these 
 filters are engaged with digital modes is rather disapointing.What 
 I mean by this is that a signal can be very clean with the 2.7 or 2.1 
 filter engaged but if  I use on of these filters the signal becomes 
 very poor.  I want to use these to isolate close in signals but there 
 appears to be a lot of distortation so they are basically of little 
 use.

 I am betting that there is more to this gain setting than meets the 
 eye and that is where my problem is.  I have put the gain for these 
 two filters at 1 and the 2.1  2.7 at zero.

 I will be playing around with the settings, but there is a method to 
 set this parameter so I need to learn what and why so I can make them 
 work the way they are supposed to work.

 Thanks and have a great holiday.

 Don
 KD8NNU
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Re: [Elecraft] K3 Roofing Filter Gain Setup

[Dick Dievendorff]

There are recommendations in the K3 Owner's manual (see Crystal Filter
Setup, indexed, on page 46) :

Use VFO A to set the gain in dB. In general, you'll want to add 1-2 dB for
400-500 Hz filters, and 3-4 dB for 200-250 Hz filters. 

and there is a table (with essentially the same guidance) in K3 Utility Help
for the Filter Configuration page. I've lost the table formatting in
cut/paste from Help, but here's the information:

Narrow crystal filters tend to have more passband loss than wide filters.
You can compensate for this effect by specifying an amount of added gain to
use for each filter in receive mode. Enter the desired gain boost, in
decibels, for each filter. You may specify a value between 0 and 8 dB. 

Elecraft recommends using the initial loss compensation values below. You
may wish to further adjust the values for your particular filters. 

Part Number Bandwidth Gain 

KFL3A-200 0.20 kHz 3-4 dB 
KFL3A-250 0.25 kHz 3-4 dB 
KFL3A-400 0.40 kHz 1-2 dB 
KFL3A-500 0.50 kHz 1-2 dB 
KFL3A-1.0K 1.00 kHz 0 dB 
KFL3A-1.8K 1.80 kHz 0 dB 
KFL3A-2.1K 2.10 kHz 0 dB 
KFL3A-2.7K 2.70 kHz 0 dB 
KFL3A-2.8K 2.80 kHz 0 dB 
KFL3A-6K 6.00 kHz 0 dB 
KFL3B-FM 13.00 kHz 0 dB

73 de Dick, K6KR


-Original Message-
From: elecraft-boun...@mailman.qth.net
[mailto:elecraft-boun...@mailman.qth.net] On Behalf Of gold...@charter.net
Sent: Saturday, May 28, 2011 12:17 PM
To: Elecraft
Subject: [Elecraft] K3 Roofing Filter Gain Setup

Gents,

I am searching without much luck for recommendations for the gain setting
recommendations for roofing filters.

Specfically I have a 700 hz 8 pole and a 200 hz filter 5 pole.   There 
is a gain setting in the k3 setup menue and I remember there were
recomendations on how to choose this setting.  However, I have not been able
to find reference on the net.

Please can anyone provide some guidance as the performance when these 
filters are engaged with digital modes is rather disapointing.What I 
mean by this is that a signal can be very clean with the 2.7 or 2.1 filter
engaged but if  I use on of these filters the signal becomes very poor.  I
want to use these to isolate close in signals but there appears to be a lot
of distortation so they are basically of little use.

I am betting that there is more to this gain setting than meets the eye and
that is where my problem is.  I have put the gain for these two filters at 1
and the 2.1  2.7 at zero.

I will be playing around with the settings, but there is a method to set
this parameter so I need to learn what and why so I can make them work the
way they are supposed to work.

Thanks and have a great holiday.

Don
KD8NNU
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Re: [Elecraft] K3 - Roofing filter for SWLing

[David Woolley (E.L)]

[EMAIL PROTECTED] wrote:

I read, with interest, the discussion about the K3's inability to

+ copy (or perhaps a better way to say it is to reproduce the audio of)
+ shortwave broadcast stations well without a wide FM filter. I just

The problem isn't for shortwave broadcast stations in general, most of 
which are already restricted to the AM filter bandwidth, but for certain 
ones, particularly intra-USA ones, that use more than one 5kHz channel.


+ wondered if there is not, or could not be made, a provision to have no
+ roofing filter for someone who wants to listen to shortwave. I haven't

This has already been covered, more than once.  Without the filter, one 
will get image responses at 30kHz less twice the DSP IF filter 
bandwidth.  You will also, probably, get aliasing at other frequencies. 
 You may also get desensitisation and IMD, as the result of signals 
that not actually aliased into the DSP filer bandwidth.


The LC filter, that others have  proposed, may be enough to constrain to 
reject BC to BC interference, unless you are listening to something well 
out of area, but no filter at all is a non-starter.


I believe there is a certain amount of LC filtering built in, but that 
will not be designed to provide adequate image rejecting and elimination 
of other close in aliases.



--
David Woolley
The Elecraft list is a forum for the discussion of topics related to 
Elecraft products and more general topics related ham radio

List Guidelines http://www.elecraft.com/elecraft_list_guidelines.htm
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Re: [Elecraft] K3 - Roofing filter for SWLing

[David Woolley (E.L)]

David Woolley (E.L) wrote:

This has already been covered, more than once.  Without the filter, one 
will get image responses at 30kHz less twice the DSP IF filter 


Sorry, I meant twice the audio bandwidth.  For AM it is the IF bandwidth.

bandwidth.  You will also, probably, get aliasing at other frequencies. 



--
David Woolley
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Elecraft products and more general topics related ham radio

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[Elecraft] K3 - Roofing filter for SWLing

[jpk5lad]

I read, with interest, the discussion about the K3's inability to copy (or 
perhaps a better way to say it is to reproduce the audio of) shortwave 
broadcast stations well without a wide FM filter.  I just wondered if there is 
not, or could not be made, a provision to have no roofing filter for someone 
who wants to listen to shortwave.  I haven't done a lot of shortwave listening 
but is there actually even a need to have the selectivity benefits of a roofing 
filter for SWLing?  Perhaps there is.

I am still awaiting my K3 so I ask this as an anxious observer, but I do have 
the 
extra bandpass filters as part of my order.  Since receivers for years did not 
have roofing filters, it's obvious that some receivers can operate without one. 
 This would just let the DSP provide the necessary selectivity.  The K3 may not 
have, or want, that ability.

I realize that asking for a super-deluxe receiver to be able to remove a 
roofing 
filter is a bit like buying a Rolls Royce without the engine and replacing the 
engine with a riding lawnmower engine.

Just a curious question... while I impatiently wait.

Jim - K5LAD

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[Elecraft] K3 roofing filter IMD

[Dave Hachadorian]

I was perusing the Sherwood Engineering receiver evaluation 
data, http://www.sherweng.com/table.html , and I noticed 
that the K3 2 KHz dynamic range is reported to be 
significantly better with the 200 Hz 5-pole roofing filter 
than with the 400 or 500 Hz filter.


Then I came across some IMD data on the K3 Wiki, 
http://www.zerobeat.net/mediawiki/index.php/K3_Roofing_Filters , 
which does not show much difference between those filters, 
but has an interesting footnote:
It should be mentioned that in a published review of the 
K3, G4AON observed degradation of close-spaced IMD 
measurements with the 400 Hz, 8 pole filter: These figures 
are for a 400 Hz bandwidth with the 8 pole 400 Hz roofing 
filter, the rather surprising discovery was the dynamic 
range improved by almost 10 dB when the 2.8 KHz 8 pole 
filter was selected. G4AON's findings haven't yet been 
independently

confirmed however.

Any thoughts on resolving these apparent inconsistencies?

Dave Hachadorian, K6LL
Yuma, AZ






















.


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[Elecraft] K3 roofing filter IMD

[Bill Tippett]

K6LL:

I was perusing the Sherwood Engineering receiver evaluation
data, 
http://www.sherweng.com/table.htmlhttp://www.sherweng.com/table.html 
, and I noticed

that the K3 2 KHz dynamic range is reported to be
significantly better with the 200 Hz 5-pole roofing filter
than with the 400 or 500 Hz filter.

Then I came across some IMD data on the K3 Wiki,
http://www.zerobeat.net/mediawiki/index.php/K3_Roofing_Filtershttp://www.zerobeat.net/mediawiki/index.php/K3_Roofing_Filters 
,

which does not show much difference between those filters,
but has an interesting footnote:
It should be mentioned that in a published review of the
K3, G4AON observed degradation of close-spaced IMD
measurements with the 400 Hz, 8 pole filter: These figures
are for a 400 Hz bandwidth with the 8 pole 400 Hz roofing
filter, the rather surprising discovery was the dynamic
range improved by almost 10 dB when the 2.8 KHz 8 pole
filter was selected. G4AON's findings haven't yet been
independently
confirmed however.

Any thoughts on resolving these apparent inconsistencies?

My guess is G4AON had a measurement problem when
he originally published that.  The current version of Dave's
review has no such comment anywhere to be found:

Two tone dynamic range testing was only possible on 14 MHz as I only 
have one signal generator, the other being a well buffered 14 MHz 
fixed crystal oscillator based on the design for dynamic range 
testing from the book Solid state design for the radio amateur. 
Both these were combined in a hybrid coupler and fed via a variable 
attenuator to the K3. The factory figures give a 100 dB dynamic range 
at 5 KHz spacing and 95 dB for a 2 KHz spacing, both using a 400 Hz 
(8 pole) filter. My measurements give a two tone dynamic range at 2 
KHz signal spacing of 100dB with the pre-amp off. These figures are 
for a 400 Hz bandwidth with the 8 pole 400 Hz roofing filter, similar 
high dynamic range figures exceeding 100 dB at close signal spacing 
were also obtained by the ARRL (review in April 2008 QST), two other 
amateurs and also by Rob Sherwood the well known receiver tester, 
these tests were independent of each other and on different K3s. 


http://www.astromag.co.uk/k3/

It should have been a clue that there was a measurement
problem when better performance was obtained with a wider
filter...that simply doesn't make sense.  ARRL has published
a few strange results (like better performance with preamp on
versus preamp off) for other products so I think everyone makes
a few measurement or data recording errors at times.  It's also
important to remember that everything we read on the Internet
is not always true!

I believe the results from Sherwood, ARRL and Elecraft
have all been consistent so far (with the exception that Sherwood
uses a classical technique of measuring IMD which may result in
phase noise limited measurements).  ARRL and Elecraft use a
narrow bandwidth spectrum analyzer (which eliminates phase noise
effects) which makes their results look better that is actually
achievable in practice (i.e. phase noise masks IMD performance).

73,  Bill  W4ZV




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[Elecraft] K3 roofing filter IMD

[Dave G4AON]

Dave

The measurement was real, however re-testing gave inconsistent results 
and varied depending on which side of the two signals the IMD 
measurement was taken. It is possible the 8 pole 400 Hz filter may have 
a blip in it's response, equally my home made signal source and hybrid 
coupler may introduce a strange artefact. However, switching the filters 
between 8 pole 400 Hz and 8 pole 2.8 KHz gave a clear spurious signal on 
the narrower filter that wasn't present with the wider one.


As others weren't able to reproduce the effect with their K3s, it seemed 
to make sense to remove reference to the issue from my web site. I 
didn't want to add to the existing debate over which filters to buy!


73 Dave, G4AON
K3/100 #80


I was perusing the Sherwood Engineering receiver evaluation
data, http://www.sherweng.com/table.html , and I noticed
that the K3 2 KHz dynamic range is reported to be
significantly better with the 200 Hz 5-pole roofing filter
than with the 400 or 500 Hz filter.

Then I came across some IMD data on the K3 Wiki,
http://www.zerobeat.net/mediawiki/index.php/K3_Roofing_Filters ,
which does not show much difference between those filters,
but has an interesting footnote:
It should be mentioned that in a published review of the
K3, G4AON observed degradation of close-spaced IMD
measurements with the 400 Hz, 8 pole filter: These figures
are for a 400 Hz bandwidth with the 8 pole 400 Hz roofing
filter, the rather surprising discovery was the dynamic
range improved by almost 10 dB when the 2.8 KHz 8 pole
filter was selected. G4AON's findings haven't yet been
independently
confirmed however.

Any thoughts on resolving these apparent inconsistencies?

Dave Hachadorian, K6LL
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[Elecraft] K3: Roofing Filter passband specs

[Larry Molitor]

It was my intent to order a K3 when they were
available from stock. Looking at the demand/supply
curve, it would seem I will be long dead and buried
before that will happen so I'm now looking very
closely at those attributes which directly affect the
usability of the radio in my particular environment. 

The roofing filter plots I see published have poor
resolution and it's not possible to determine the
passband ripple from them. I think this has been
addressed on the list in the past, but I don't
remember any better data being mentioned. If there is
better passband data can someone point me to it?

I'm concerned because in the past when I've
characterized INRAD crystal filters, they have had
very poor passband response resulting in degraded weak
signal performance. In their defense, I have not had
the opportunity to look at any recent production
filters so maybe it's not an issue anymore.

Lacking any better data it appears to me the best
roofing filter option for very weak signal CW and data
modes is the standard 5 pole 2.7 kHz filter.

Thanks.

Larry - W7IUV



  

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Re: [Elecraft] K3 roofing filter group delay

[John, KI6WX]

Don;
Don't forget Bessel filters.  These are maximally flat for group delay, but 
have a much slower rolloff.


A 5-pole 500-Hz 0.5 dB Chebyshev will be down 80 dB at 1 kHz and will have a 
group delay of 16 ms at band center and 44 ms at -3 dB.  A 5-pole 500-Hz 
Bessel filter will be down 40 dB at 1 kHz and have a constant group delay 
across the passband of 10 ms.


You can have a flat group delay or a fast rolloff, but you can't have both.

-John
KI6WX



Brian and all,

The number of poles is not the primary deciding factor.  It is the type of 
filter (Cohn, Chebychev, Butterworth, Gaussian to 6 dB, Gaussian to 12 dB, 
etc.) that will influence the group delay.  See the discussion on filters 
in Experimental Methods for RF Design for further information.


In general, those filters with a 'rounded nose' will have the best group 
delay characteristics - but that is only a generalization, the details 
will tell the rest of the story.


73,
Don W3FPR

Brian Lloyd wrote:
A number of messages have gone back and forth here about roofing filters. 
We did mention group delay but I wonder if Elecraft can provide group 
delay characteristics for the various filters offered for the K3.


Seems to me that, in general, fewer poles tend to provide better group 
delay in a filter at the expense of the skirts. OTOH, if the skirts in 
the roofing filter are sufficient to attenuate a strong, undesired signal 
so that it cannot cause desense, then it strikes me that the 5-pole 
filters might actually provide superior performance for digital 
communications.


73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com




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Re: [Elecraft] K3 roofing filter group delay

[Don Wilhelm]

John,

Thanks for that additional info - I had forgotten about the Bessel filter.

There is a distinct advantage with the K3, the 'roofing filter' is not 
the major element in setting the rolloff of the total filtering and the 
ultimate receiver selectivity because that aspect is handled by the DSP. 
 That makes the use of roofing filters with a slow rolloff (not steep 
skirts) quite feasible.


I believe we should be looking at group delay filter characteristics 
more closely for use with data modes, especially with the advent of 
digital voice mode.


73,
Don W3FPR

John, KI6WX wrote:

Don;
Don't forget Bessel filters.  These are maximally flat for group delay, 
but have a much slower rolloff.


A 5-pole 500-Hz 0.5 dB Chebyshev will be down 80 dB at 1 kHz and will 
have a group delay of 16 ms at band center and 44 ms at -3 dB.  A 5-pole 
500-Hz Bessel filter will be down 40 dB at 1 kHz and have a constant 
group delay across the passband of 10 ms.


You can have a flat group delay or a fast rolloff, but you can't have both.

-John
KI6WX



Brian and all,

The number of poles is not the primary deciding factor.  It is the 
type of filter (Cohn, Chebychev, Butterworth, Gaussian to 6 dB, 
Gaussian to 12 dB, etc.) that will influence the group delay.  See the 
discussion on filters in Experimental Methods for RF Design for 
further information.


In general, those filters with a 'rounded nose' will have the best 
group delay characteristics - but that is only a generalization, the 
details will tell the rest of the story.


73,
Don W3FPR

Brian Lloyd wrote:
A number of messages have gone back and forth here about roofing 
filters. We did mention group delay but I wonder if Elecraft can 
provide group delay characteristics for the various filters offered 
for the K3.


Seems to me that, in general, fewer poles tend to provide better 
group delay in a filter at the expense of the skirts. OTOH, if the 
skirts in the roofing filter are sufficient to attenuate a strong, 
undesired signal so that it cannot cause desense, then it strikes me 
that the 5-pole filters might actually provide superior performance 
for digital communications.


73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com







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Re: [Elecraft] K3 roofing filter group delay

[Jack Smith]

Don:

Another interesting classical design is the equal-ripple-delay filter. 
It uses the Chebyshev concept of allowing ripple in the passband to 
provide increased skirt selectivity, except that the ripple that is 
allowed is in the delay function, not the amplitude. By allowing a 
slight amount of ripple in group delay of an equaphase filter, the 
skirts can be improved over similar order filter with a flat group delay.


Also -- since the K3's roofing filters are backed up with a DSP, could 
not the DSP implement a delay equalizer, so that the net delay is flat?  
I also don't know whether the roofing filters are repeatable enough to 
permit a single equalization setting or if each filter will require 
custom coefficients. (If so, I suppose each filter could be equipped 
with a small EEPROM chip with its equalization parameters, to be read 
when a new filter is installed into a K3.)


I don't know if the K3's DSP implements IIR or FIR filters, but an FIR 
can be implemented with linear phase (flat group delay) Hence, if FIR 
filters are used, the only group delay requiring equalization will be 
the crystal roofing filter.



Jack K8ZOA
www.cliftonlaboratories.com




Don Wilhelm wrote:

John,

Thanks for that additional info - I had forgotten about the Bessel 
filter.


There is a distinct advantage with the K3, the 'roofing filter' is not 
the major element in setting the rolloff of the total filtering and 
the ultimate receiver selectivity because that aspect is handled by 
the DSP.  That makes the use of roofing filters with a slow rolloff 
(not steep skirts) quite feasible.


I believe we should be looking at group delay filter characteristics 
more closely for use with data modes, especially with the advent of 
digital voice mode.


73,
Don W3FPR

John, KI6WX wrote:

Don;
Don't forget Bessel filters.  These are maximally flat for group 
delay, but have a much slower rolloff.


A 5-pole 500-Hz 0.5 dB Chebyshev will be down 80 dB at 1 kHz and will 
have a group delay of 16 ms at band center and 44 ms at -3 dB.  A 
5-pole 500-Hz Bessel filter will be down 40 dB at 1 kHz and have a 
constant group delay across the passband of 10 ms.


You can have a flat group delay or a fast rolloff, but you can't have 
both.


-John
KI6WX



Brian and all,

The number of poles is not the primary deciding factor.  It is the 
type of filter (Cohn, Chebychev, Butterworth, Gaussian to 6 dB, 
Gaussian to 12 dB, etc.) that will influence the group delay.  See 
the discussion on filters in Experimental Methods for RF Design for 
further information.


In general, those filters with a 'rounded nose' will have the best 
group delay characteristics - but that is only a generalization, the 
details will tell the rest of the story.


73,
Don W3FPR

Brian Lloyd wrote:
A number of messages have gone back and forth here about roofing 
filters. We did mention group delay but I wonder if Elecraft can 
provide group delay characteristics for the various filters offered 
for the K3.


Seems to me that, in general, fewer poles tend to provide better 
group delay in a filter at the expense of the skirts. OTOH, if the 
skirts in the roofing filter are sufficient to attenuate a strong, 
undesired signal so that it cannot cause desense, then it strikes 
me that the 5-pole filters might actually provide superior 
performance for digital communications.


73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com







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Re: [Elecraft] K3 roofing filter group delay

[John Magliacane]

 Don't forget Bessel filters.  These are maximally flat for group delay, but 
 have a much slower rolloff.

John,

What penalty (if any) would occur in cascading identical Bessel filters to
improve roll-off and stop-band attenuation?

Would the overall response still be considered Bessel, or will a point be
reached where the response begins to take on Chebyshev characteristics?

Thanks.


73, de John, KD2BD


Visit John on the Web at:

http://kd2bd.ham.org/
.
.
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.


   
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Re: [Elecraft] K3 roofing filter group delay

[Brian Lloyd]

On May 13, 2007, at 11:18 PM, John, KI6WX wrote:


Don;
Don't forget Bessel filters.  These are maximally flat for group  
delay, but have a much slower rolloff.


A 5-pole 500-Hz 0.5 dB Chebyshev will be down 80 dB at 1 kHz and  
will have a group delay of 16 ms at band center and 44 ms at -3  
dB.  A 5-pole 500-Hz Bessel filter will be down 40 dB at 1 kHz and  
have a constant group delay across the passband of 10 ms.


You can have a flat group delay or a fast rolloff, but you can't  
have both.


Right. TANSTAAFL (there ain't no such thing as a free lunch). Given  
that we can get very steep skirts in DSP at the expense of  
introducing more overall latency (delay) in the filter (usually not a  
problem for what we are doing), then we can probably accept analog  
roofing filters that don't provide the same ultimate attenuation in  
the skirts.


Given the choice between the two filters I would probably opt for the  
Bessel filter myself.


So, Elecraft, will you be offering a group of roofing filters  
optimized for digital communications? How about your brick wall  
filters in DSP?


73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com


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Re: [Elecraft] K3 roofing filter group delay

[Brian Lloyd]

On May 14, 2007, at 5:32 AM, Don Wilhelm wrote:


John,

Thanks for that additional info - I had forgotten about the Bessel  
filter.


There is a distinct advantage with the K3, the 'roofing filter' is  
not the major element in setting the rolloff of the total filtering  
and the ultimate receiver selectivity because that aspect is  
handled by the DSP.  That makes the use of roofing filters with a  
slow rolloff (not steep skirts) quite feasible.


I believe we should be looking at group delay filter  
characteristics more closely for use with data modes, especially  
with the advent of digital voice mode.


That is especially true if you are trying to put all your bits on one  
carrier. If you opt for something like OFDM (multiple carriers) and a  
lower symbol rate, each carrier and its sidebands will be narrower  
and will not have as much delay skew across that carrier and its  
sidebands. In that case center-to-edge group delay spread is less  
harmful.


OTOH, it will be critical for trying to dig a really weak narrow  
signal out.


Yeah, I agree with you. I really want to see what the filters are  
going to look like.


73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com


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Re: [Elecraft] K3 roofing filter group delay

[John, KI6WX]

You can cascade a pair of Bessel filters to get better frequency response 
while maintaining a flat group delay, but you do have to isolate them so 
that they both are seeing a resistive source and load impedance.  The 
cascaded filters would show a 6 dB rolloff at nominal cutoff frequency.  The 
3 dB point will occur at about 70% of bandwidth.  A pair of 5-pole Bessel 
filters cascaded with a 500 Hz 3 dB bandwidth will be down about 55 dB at 1 
kHz.


The better method is to build a 10-pole 500-Hz Bessel filter which will be 
down nearly 60 dB at 1 kHz.


There was also a question about a linear phase filter with equiripple error. 
A 0.5 degree error is about +/-5% variation in group delay.  A 5-pole 500-Hz 
0.5 degree equiripple filter will be down 50 dB at 1 kHz and have about 11 
ms of group delay.

-John
KI6WX


Don't forget Bessel filters.  These are maximally flat for group delay, 
but

have a much slower rolloff.


John,

What penalty (if any) would occur in cascading identical Bessel filters to
improve roll-off and stop-band attenuation?

Would the overall response still be considered Bessel, or will a point be
reached where the response begins to take on Chebyshev characteristics?



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[Elecraft] K3 roofing filter group delay

[Brian Lloyd]

A number of messages have gone back and forth here about roofing  
filters. We did mention group delay but I wonder if Elecraft can  
provide group delay characteristics for the various filters offered  
for the K3.


Seems to me that, in general, fewer poles tend to provide better  
group delay in a filter at the expense of the skirts. OTOH, if the  
skirts in the roofing filter are sufficient to attenuate a strong,  
undesired signal so that it cannot cause desense, then it strikes me  
that the 5-pole filters might actually provide superior performance  
for digital communications.


73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com


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Re: [Elecraft] K3 roofing filter group delay

[Don Wilhelm]

Brian and all,

The number of poles is not the primary deciding factor.  It is the type 
of filter (Cohn, Chebychev, Butterworth, Gaussian to 6 dB, Gaussian to 
12 dB, etc.) that will influence the group delay.  See the discussion on 
filters in Experimental Methods for RF Design for further information.


In general, those filters with a 'rounded nose' will have the best group 
delay characteristics - but that is only a generalization, the details 
will tell the rest of the story.


73,
Don W3FPR

Brian Lloyd wrote:
A number of messages have gone back and forth here about roofing 
filters. We did mention group delay but I wonder if Elecraft can provide 
group delay characteristics for the various filters offered for the K3.


Seems to me that, in general, fewer poles tend to provide better group 
delay in a filter at the expense of the skirts. OTOH, if the skirts in 
the roofing filter are sufficient to attenuate a strong, undesired 
signal so that it cannot cause desense, then it strikes me that the 
5-pole filters might actually provide superior performance for digital 
communications.


73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com


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