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adding 250Hz filer, any improvement?

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Jorge Diez - CX6VM

adding 250Hz filer, any improvement?

Hello,

I have both KFL3A-400 (400 Hz 8-pole) and KFL3A-1.8K (1.8 kHz 8-pole)
filters in my K3.

If I add a KFL3A-250 (250 Hz 8-pole) filter I will notice it better to use
in contests? Or with the 400Hz is enough? Notice I am not in USA or EU
with strong stations near me, I don´t have the QRM this big populations
have, trying to reduce the splatters.

73,

Jorge

CX6VM/CW5W

k3 #4077

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Rex Lint

Re: adding 250Hz filer, any improvement?

If you have strong stations closer to your frequency than 400 hz, then the
250 hz filter will get rid of them down to 250 hz of your frequency. If the
stations that are near you are not strong, the DSP filter will handle it OK.

-Rex-

K1HI
Rex Lint
Merrimack, NH
WWW.QRZ.COM/db/k1hi

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Jorge Diez - CX6VM
Sent: Tuesday, February 08, 2011 12:50 PM
To: [hidden email]
Subject: [Elecraft] adding 250Hz filer, any improvement?

Hello,

I have both KFL3A-400 (400 Hz 8-pole) and KFL3A-1.8K (1.8 kHz 8-pole)
filters in my K3.

If I add a KFL3A-250 (250 Hz 8-pole) filter I will notice it better to use
in contests? Or with the 400Hz is enough? Notice I am not in USA or EU
with strong stations near me, I don´t have the QRM this big populations
have, trying to reduce the splatters.

73,

Jorge

CX6VM/CW5W

k3 #4077

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Jim Brown-10

Re: adding 250Hz filer, any improvement?

In reply to this post by Jorge Diez - CX6VM

On 2/8/2011 9:49 AM, Jorge Diez - CX6VM wrote:
> If I add a KFL3A-250 (250 Hz 8-pole) filter I will notice it better to use
> in contests? Or with the 400Hz is enough?

Jorge,

I find that the 250 Hz filter helps a lot when there are strong signals
very close to a weak station. I bought one a year or so ago to try, and
quickly bought two more for each RX (I have one radio with a sub-RX). I
recently bought a third K3 with one RX and a 400 Hz filter. I plan to
add a 250 Hz filter to it as well.

73, Jim K9YC
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Scott Ellington

Re: adding 250Hz filer, any improvement?

In reply to this post by Jorge Diez - CX6VM

QRM levels are generally much lower outside EU or NA. Years ago, I did a CW contest from ZL with a TS-50 and a single 500 Hz filter. That would have been woefully inadequate in NA, but it was fine there. So, the question I would ask is whether anyone in a non-EU or NA QTH has compared the K3 400 Hz filter with narrower DSP with the 250 Hz filter. Surely, the 400 Hz fliter +DSP would be far superior to that old TS-50, so I would expect it to be fine. Note that the K3 "250 Hz" filter is really about 370 Hz wide, compared to 435 for the "400 Hz" one, so the difference isn't that great, anyway.

Perhaps Jorge can check this out in the next contest: Set the "I" filter to 400 Hz, and the "II" filter to 250 Hz, both with the 400 Hz xtal filter. I'd be interested in the results.

73,

Scott K9MA

On Feb 8, 2011, at 11:49 AM, Jorge Diez - CX6VM wrote:

Dave Hachadorian

Re: adding 250Hz filer, any improvement?

I had both filters installed for a while. They both work equally well.
The 250 produces a beautifully symmetrical, optimal width, spectral plot on
the MMTTY FFT display for RTTY, so I decided to standardize on that filter,
and sold the 400. Now I have 250's in both of my K3's. I told the K3's
that the filters were 400's, so they switch in at that dsp bandwidth.

Dave Hachadorian, K6LL
Yuma, AZ

-----Original Message-----
From: Scott Ellington
Sent: Tuesday, February 08, 2011 12:07 PM
To: Elecraft Reflector
Subject: Re: [Elecraft] adding 250Hz filer, any improvement?

QRM levels are generally much lower outside EU or NA. Years ago, I did a
CW contest from ZL with a TS-50 and a single 500 Hz filter. That would
have been woefully inadequate in NA, but it was fine there. So, the
question I would ask is whether anyone in a non-EU or NA QTH has compared
the K3 400 Hz filter with narrower DSP with the 250 Hz filter. Surely, the
400 Hz fliter +DSP would be far superior to that old TS-50, so I would
expect it to be fine. Note that the K3 "250 Hz" filter is really about 370
Hz wide, compared to 435 for the "400 Hz" one, so the difference isn't that
great, anyway.

Perhaps Jorge can check this out in the next contest: Set the "I" filter
to 400 Hz, and the "II" filter to 250 Hz, both with the 400 Hz xtal filter.
I'd be interested in the results.

73,

Scott K9MA

On Feb 8, 2011, at 11:49 AM, Jorge Diez - CX6VM wrote:

> Hello,
>
>
>
> I have both KFL3A-400 (400 Hz 8-pole) and KFL3A-1.8K (1.8 kHz 8-pole)
> filters in my K3.
>
>
>
> If I add a KFL3A-250 (250 Hz 8-pole) filter I will notice it better to
> use
> in contests? Or with the 400Hz is enough? Notice I am not in USA or EU
> with strong stations near me, I don´t have the QRM this big populations
> have, trying to reduce the splatters.
>
>
>
> 73,
>
> Jorge
>
> CX6VM/CW5W
>
> k3 #4077

Scott Ellington
Madison, Wisconsin
USA

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Joe Subich, W4TV-4

Re: adding 250Hz filer, any improvement?

In reply to this post by Jorge Diez - CX6VM

The "250 Hz" filter has a nominal -6dB bandwidth of 350 to 370 Hz
(see plots at http://www.elecraft.com/K3/filter_plots/250.gif and
www.inrad.net). The 400 Hz filter has a nominal -6dB bandwidth
of 430 - 450 Hz (plots at the same sites).

Since the ultimate selectivity is generated by the DSP, *not* the
first IF filter, the difference in protection against strong adjacent
signals would be minimal (less than 50 Hz on either side). There
would seem to be little practical difference between the two and
no justification for adding one if the other is already fitted.

If one already had the 400 Hz filter, adding the 200 Hz Elecraft
filter (narrower than the "250 Hz" Inrad down to at least -40 dB)
would make more sense.

73,

... Joe, W4TV

On 2/8/2011 12:49 PM, Jorge Diez - CX6VM wrote:

> Hello,
>
>
>
> I have both KFL3A-400 (400 Hz 8-pole) and KFL3A-1.8K (1.8 kHz 8-pole)
> filters in my K3.
>
>
>
> If I add a KFL3A-250 (250 Hz 8-pole) filter I will notice it better to use
> in contests? Or with the 400Hz is enough? Notice I am not in USA or EU
> with strong stations near me, I don´t have the QRM this big populations
> have, trying to reduce the splatters.
>
>
>
> 73,
>
> Jorge
>
> CX6VM/CW5W
>
> k3 #4077
>
> ______________________________________________________________
> 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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wayne burdick

Re: adding 250Hz filer, any improvement?

Administrator

In reply to this post by Scott Ellington

On the other end of the spectrum: If the going is really tough, you
might consider our 200 Hz, 5-pole filter. It's a favorite of CW and
data-mode operators who routinely have to dig for weak ones between
monster signals in CW and data modes.

73,
Wayne
N6KR

On Feb 8, 2011, at 11:07 AM, Scott Ellington wrote:

> QRM levels are generally much lower outside EU or NA. Years ago, I
> did a CW contest from ZL with a TS-50 and a single 500 Hz filter.
> That would have been woefully inadequate in NA, but it was fine
> there. So, the question I would ask is whether anyone in a non-EU
> or NA QTH has compared the K3 400 Hz filter with narrower DSP with
> the 250 Hz filter. Surely, the 400 Hz fliter +DSP would be far
> superior to that old TS-50, so I would expect it to be fine. Note
> that the K3 "250 Hz" filter is really about 370 Hz wide, compared to
> 435 for the "400 Hz" one, so the difference isn't that great, anyway.
>
> Perhaps Jorge can check this out in the next contest: Set the "I"
> filter to 400 Hz, and the "II" filter to 250 Hz, both with the 400
> Hz xtal filter. I'd be interested in the results.
>
> 73,
>
> Scott K9MA
>
>
>
> On Feb 8, 2011, at 11:49 AM, Jorge Diez - CX6VM wrote:
>
>> Hello,
>>
>>
>>
>> I have both KFL3A-400 (400 Hz 8-pole) and KFL3A-1.8K (1.8 kHz 8-
>> pole)
>> filters in my K3.
>>
>>
>>
>> If I add a KFL3A-250 (250 Hz 8-pole) filter I will notice it better
>> to use
>> in contests? Or with the 400Hz is enough? Notice I am not in USA
>> or EU
>> with strong stations near me, I don´t have the QRM this big
>> populations
>> have, trying to reduce the splatters.
>>
>>
>>
>> 73,
>>
>> Jorge
>>
>> CX6VM/CW5W
>>
>> k3 #4077
>
> Scott Ellington
> Madison, Wisconsin
> USA
>
>
>
> ______________________________________________________________
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Bill W4ZV

Re: adding 250Hz filer, any improvement?

wayne burdick wrote

On the other end of the spectrum: If the going is really tough, you
might consider our 200 Hz, 5-pole filter. It's a favorite of CW and
data-mode operators who routinely have to dig for weak ones between
monster signals in CW and data modes.

I operated most of the CQ 160 (a very crowded contest with a mixture of big NA signals and weak DX signals) using a 200 Hz set to activate at WIDTH 350. This makes the XFIL/DSP cascaded curve closer to that of the 200 only. Joe W4TV provided the following a few years ago:

200 250 400 500
-------------------------------------------------
- 6dB 224 370 435 565 Hz
-60dB 896 777 913 1751 Hz
slope 6.22 3.77 4.43 10.98 Hz/dB

-10dB 274 400 470 653 Hz
-20dB 398 475 559 873 Hz
-30dB 522 550 647 1092 Hz
-40dB 647 626 736 1312 Hz
-50dB 771 702 825 1531 Hz

http://elecraft.365791.n2.nabble.com/FILTER-SETTINGS-td456756.html#a456757

With the XFIL = 200 and DSP = 350, the resulting filter is probably -15 dB at ~300 Hz, which still allows you to still hear what's going on around you. Most EU stations would call zero beat since they are accustomed to extremely tight spacings but many NA stations were off frequency. Sandwiched between two EU stations about 250 Hz on either side, a major problem was when NA stations called them on my run frequency!

I use a waterfall when doing S&P so it was very easy to jump to stations using the 200 Hz filter. I believe as more guys begin using waterfalls they will do a better job of zero beating stations running. One problem I ran into was my KRX3 only had an Inrad 500 Hz 8-pole which was definitely too wide with many strong stations were nearby. I had to turn diversity off several few times when the KRX3 was allowing too much QRM. I fixed that last week by adding another 200 Hz to the KRX3!

73, Bill

David Gilbert

Re: adding 250Hz filer, any improvement?

The waterfall in CW Skimmer is extremely accurate for that sort of
thing. Whether you mouse click on a "decoder" (station) or use the
Up/Down arrow keys to jump from one to the next, the zero beat is very,
very accurate. So much so that when I was using CW Skimmer in 3 KHz
audio mode simply to step through stations (using the arrow keys) for
S&P on VFO B, it was actually too good ... the tone for each station I
stepped through was always identical, making it sometimes difficult to
recognize that I had actually QSY'd.

The decoders in CW Skimmer home in VERY tightly.

73,
Dave AB7E

On 2/8/2011 7:12 PM, Bill W4ZV wrote:
> I use a waterfall when doing S&P so it was very easy to jump to stations
> using the 200 Hz filter. I believe as more guys begin using waterfalls they
> will do a better job of zero beating stations running.
> 73, Bill
>
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s57aw

Re: adding 250Hz filer, any improvement?

In reply to this post by wayne burdick

I found 8 pole 400 Hz and 5 pole 200 Hz as a great combination in last CQ 160m. 400 Hz filter was to wide most of the time.

73 Robert, S57AW

Sent from iPhone

Na dan 9. feb. 2011, ob 02:30, Wayne Burdick <[hidden email]> je zapisal:

> On the other end of the spectrum: If the going is really tough, you
> might consider our 200 Hz, 5-pole filter. It's a favorite of CW and
> data-mode operators who routinely have to dig for weak ones between
> monster signals in CW and data modes.
>
> 73,
> Wayne
> N6KR
>
> On Feb 8, 2011, at 11:07 AM, Scott Ellington wrote:
>
>> QRM levels are generally much lower outside EU or NA. Years ago, I
>> did a CW contest from ZL with a TS-50 and a single 500 Hz filter.
>> That would have been woefully inadequate in NA, but it was fine
>> there. So, the question I would ask is whether anyone in a non-EU
>> or NA QTH has compared the K3 400 Hz filter with narrower DSP with
>> the 250 Hz filter. Surely, the 400 Hz fliter +DSP would be far
>> superior to that old TS-50, so I would expect it to be fine. Note
>> that the K3 "250 Hz" filter is really about 370 Hz wide, compared to
>> 435 for the "400 Hz" one, so the difference isn't that great, anyway.
>>
>> Perhaps Jorge can check this out in the next contest: Set the "I"
>> filter to 400 Hz, and the "II" filter to 250 Hz, both with the 400
>> Hz xtal filter. I'd be interested in the results.
>>
>> 73,
>>
>> Scott K9MA
>>
>>
>>
>> On Feb 8, 2011, at 11:49 AM, Jorge Diez - CX6VM wrote:
>>
>>> Hello,
>>>
>>>
>>>
>>> I have both KFL3A-400 (400 Hz 8-pole) and KFL3A-1.8K (1.8 kHz 8-
>>> pole)
>>> filters in my K3.
>>>
>>>
>>>
>>> If I add a KFL3A-250 (250 Hz 8-pole) filter I will notice it better
>>> to use
>>> in contests? Or with the 400Hz is enough? Notice I am not in USA
>>> or EU
>>> with strong stations near me, I don´t have the QRM this big
>>> populations
>>> have, trying to reduce the splatters.
>>>
>>>
>>>
>>> 73,
>>>
>>> Jorge
>>>
>>> CX6VM/CW5W
>>>
>>> k3 #4077
>>
>> Scott Ellington
>> Madison, Wisconsin
>> USA
>>
>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
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>>
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>> Please help support this email list: http://www.qsl.net/donate.html
>
> ______________________________________________________________
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Edward R Cole

Re: adding 250Hz filer, any improvement?

In reply to this post by Jorge Diez - CX6VM

Let me ask a filter question for a different situation. I am
interested in receiving very-weak CW and currently have the 2.8 KHz
and 400-Hz 8-pole filters. Will narrowing the DSP bw down to 200-Hz
work as well as using a 200-Hz filter? There are no strong stations
either nearby or on the band.

BTW I am impressed with the 400-Hz filter on the K3 when compared to
the 400-Hz DSP on my FT-847 (no surprise).
I find trying to hear extremely weak-CW that narrowing down to 200,
100 or even narrower makes the difference.

I left a blank filter space on the main receive for adding a narrow
SSB filter at a later time. I also have the 13-KHz filter for
FM/AM. Sub-Rx has 2.8 and 13-KHz.

73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ 500 KHz - 10-GHz www.kl7uw.com
EME: 144-1.4kw*, 432-100w*, 1296-testing*, 3400-winter?
DUBUS Magazine USA Rep [hidden email]
======================================
*temp not in service
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Bill W4ZV

Re: adding 250Hz filer, any improvement?

Edward R. Cole wrote

Let me ask a filter question for a different situation. I am
interested in receiving very-weak CW and currently have the 2.8 KHz
and 400-Hz 8-pole filters. Will narrowing the DSP bw down to 200-Hz
work as well as using a 200-Hz filter? There are no strong stations
either nearby or on the band.

There would be no advantage to a 200 Hz XFIL in that case...but you may not want to go that narrow. I prefer a wider bandwidth (350-400 Hz) for extremely weak signals in white noise (no QRM!). I believe the human ear does a better job of discriminating signals from white noise if it has some bandwidth to work with. APF also works better for me if used with wider bandwidths for the same reasons.

The 200 Hz XFIL is mainly useful for extreme QRM situations...like the CQ 160.

73, Bill

Don Wilhelm-4

Re: adding 250Hz filer, any improvement?

In reply to this post by Edward R Cole

Ed,

If there are no strong signals on the band or nearby your receive
frequency, then any filter, even the stock 2.7 kHz is sufficient. The
only purpose of the roofing filter is to keep strong signals out of the
receiver passband so they do not activate the AGC and de-sense the
receiver for the signal you are trying to hear.

73,
Don W3FPR

On 2/9/2011 3:07 AM, Edward R. Cole wrote:

Vic K2VCO

Re: adding 250Hz filer, any improvement?

In reply to this post by Edward R Cole

I see that others have told you that you can narrow the DSP and it will be just as good as
long as there are no nearby signals greater than about S9+20.

Let me add that a huge improvement in copyability of weak CW can be gained by using the
APF in current firmware. It has a bandwidth (I believe) of about 30 Hz at 6 dB points, and
also provides a slight gain boost. It's easiest to select 1 Hz tuning steps (tab 'fine')
when tuning with it on.

I usually use a DSP bandwidth of 300-400 Hz and APF on when copying really, really weak
signals.

I know there are guys like W4ZV who have a DSP between their ears that does a better job
with wider bandwidths, but not all of us have this ability!

On 2/9/2011 12:07 AM, Edward R. Cole wrote:

> Let me ask a filter question for a different situation. I am
> interested in receiving very-weak CW and currently have the 2.8 KHz
> and 400-Hz 8-pole filters. Will narrowing the DSP bw down to 200-Hz
> work as well as using a 200-Hz filter? There are no strong stations
> either nearby or on the band.
>
> BTW I am impressed with the 400-Hz filter on the K3 when compared to
> the 400-Hz DSP on my FT-847 (no surprise).
> I find trying to hear extremely weak-CW that narrowing down to 200,
> 100 or even narrower makes the difference.
>
> I left a blank filter space on the main receive for adding a narrow
> SSB filter at a later time. I also have the 13-KHz filter for
> FM/AM. Sub-Rx has 2.8 and 13-KHz.
>
>
> 73, Ed - KL7UW, WD2XSH/45
> ======================================
> BP40IQ 500 KHz - 10-GHz www.kl7uw.com
> EME: 144-1.4kw*, 432-100w*, 1296-testing*, 3400-winter?
> DUBUS Magazine USA Rep [hidden email]
> ======================================
> *temp not in service
> ______________________________________________________________
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--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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Scott Ellington

Re: adding 250Hz filer, any improvement?

In reply to this post by Don Wilhelm-4

I agree with both Don and Bill. There are really two issues:

In the presences of just noise, the DSP with a wider crystal filter is adequate. The additional noise reduction of a narrow crystal filter is negligible. (QRM is another matter.)

The brain/ear system, at least for many operators, is very good at copying weak signals in noise, even with a broad bandwidth. If there's no QRM nearby, I always find it easier to copy with a larger bandwidth, though anything above 500 Hz makes little difference. (Except for quickly tuning across a mostly empty band.) The 250 Hz bandwidth, in my experience, ALWAYS makes it harder to copy weak signals, unless there is adjacent QRM. For that reason, I prefer to operate with 400 Hz bandwidth most of the time, switching to a narrower bandwidth only when necessary.

This seems to contradict signal theory, which says that a narrower bandwidth improves S/N ratio until the filter bandwidth is equal to that of the signal. What signal theory fails to take into account is the matched filter in a CW operator's head.

73,

Scott K9MA

On Feb 9, 2011, at 7:51 AM, Don Wilhelm wrote:

> Ed,
>
> If there are no strong signals on the band or nearby your receive
> frequency, then any filter, even the stock 2.7 kHz is sufficient. The
> only purpose of the roofing filter is to keep strong signals out of the
> receiver passband so they do not activate the AGC and de-sense the
> receiver for the signal you are trying to hear.
>
> 73,
> Don W3FPR
>
> On 2/9/2011 3:07 AM, Edward R. Cole wrote:
>> Let me ask a filter question for a different situation. I am
>> interested in receiving very-weak CW and currently have the 2.8 KHz
>> and 400-Hz 8-pole filters. Will narrowing the DSP bw down to 200-Hz
>> work as well as using a 200-Hz filter? There are no strong stations
>> either nearby or on the band.
>>
>> BTW I am impressed with the 400-Hz filter on the K3 when compared to
>> the 400-Hz DSP on my FT-847 (no surprise).
>> I find trying to hear extremely weak-CW that narrowing down to 200,
>> 100 or even narrower makes the difference.
>>
>> I left a blank filter space on the main receive for adding a narrow
>> SSB filter at a later time. I also have the 13-KHz filter for
>> FM/AM. Sub-Rx has 2.8 and 13-KHz.
>>
>>
> ______________________________________________________________
> Elecraft mailing list
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Jessie Oberreuter-2

Re: adding 250Hz filer, any improvement?

I've noticed this effect myself. At super narrow bandwidths, the
signal and remaining noise are both essentially on the same frequency.
With nothing else around to provide a base-line reference, discrimination
becomes a function of real-time delta power measurement rather than tone
detection. My ears and brain are more sensitive to frequency information
than power information, and perform poorly under such conditions. I
suspect this is true for most other people as well. Open the bandwidth up
a bit, and the ear/brain system is back on familiar ground.
Some experiments are suggested, eg replacing the signal with a clean
generated tone at the dynamic power level as measured by the DSP,
injecting surrounding "clean" white noise around the filter, or both if we
want to make it sound like radio even if, at this point, it's a virtual
signal :).

On Wed, 9 Feb 2011, Scott Ellington wrote:

> I agree with both Don and Bill. There are really two issues:
>
> In the presences of just noise, the DSP with a wider crystal filter is adequate. The additional noise reduction of a narrow crystal filter is negligible. (QRM is another matter.)
>
> The brain/ear system, at least for many operators, is very good at copying weak signals in noise, even with a broad bandwidth. If there's no QRM nearby, I always find it easier to copy with a larger bandwidth, though anything above 500 Hz makes little difference. (Except for quickly tuning across a mostly empty band.) The 250 Hz bandwidth, in my experience, ALWAYS makes it harder to copy weak signals, unless there is adjacent QRM. For that reason, I prefer to operate with 400 Hz bandwidth most of the time, switching to a narrower bandwidth only when necessary.
>
> This seems to contradict signal theory, which says that a narrower bandwidth improves S/N ratio until the filter bandwidth is equal to that of the signal. What signal theory fails to take into account is the matched filter in a CW operator's head.
>
> 73,
>
> Scott K9MA
>
> On Feb 9, 2011, at 7:51 AM, Don Wilhelm wrote:
>
>> Ed,
>>
>> If there are no strong signals on the band or nearby your receive
>> frequency, then any filter, even the stock 2.7 kHz is sufficient. The
>> only purpose of the roofing filter is to keep strong signals out of the
>> receiver passband so they do not activate the AGC and de-sense the
>> receiver for the signal you are trying to hear.
>>
>> 73,
>> Don W3FPR
>>
>> On 2/9/2011 3:07 AM, Edward R. Cole wrote:
>>> Let me ask a filter question for a different situation. I am
>>> interested in receiving very-weak CW and currently have the 2.8 KHz
>>> and 400-Hz 8-pole filters. Will narrowing the DSP bw down to 200-Hz
>>> work as well as using a 200-Hz filter? There are no strong stations
>>> either nearby or on the band.
>>>
>>> BTW I am impressed with the 400-Hz filter on the K3 when compared to
>>> the 400-Hz DSP on my FT-847 (no surprise).
>>> I find trying to hear extremely weak-CW that narrowing down to 200,
>>> 100 or even narrower makes the difference.
>>>
>>> I left a blank filter space on the main receive for adding a narrow
>>> SSB filter at a later time. I also have the 13-KHz filter for
>>> FM/AM. Sub-Rx has 2.8 and 13-KHz.
>>>
>>>
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>
> Scott Ellington
> Madison, Wisconsin
> USA
>
>
>
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Jim Brown-10

Re: adding 250Hz filer, any improvement?

In reply to this post by Scott Ellington

On 2/9/2011 8:23 AM, Scott Ellington wrote:
> The additional noise reduction of a narrow crystal filter is negligible.

Right. While a narrower filter reduces the noise bandwidth, the ringing
of a filter with steeper slopes may increase the effects of impulse noise.

> (QRM is another matter.)

Yes. When there are two filters in the signal chain with electronics
between them to prevent interaction, the rejection capabilities of those
filters will ADD. This addition is called CASCADING.

Putting some hypothetical numbers to it, let's say that the IF filter is
down by 6 dB 125 Hz from center and 20 dB down at 300 Hz. If we add a
roofing filter that is 6dB down at 125 Hz and 15 dB down at 300 Hz, the
cascaded response of the receiver will be 12 dB down at 125 Hz and 35 dB
down at 300 Hz. The difference in rejection of slightly off-frequency
QRM is quite significant, and is clearly heard in crowded band conditions.

Cascading is most dramatic when the two filters have the same
bandwidth. As one filter is made more narrow, the addition of the wider
filter still adds rejection, but it adds less rejection, and that added
rejection is greatest farther off frequency.

73, Jim K9YC
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Igor Sokolov-2

2 x K3 in SO3R at R9DX

http://www.youtube.com/watch?v=Wbj76DVuAoo

This is a video tour around R9DX (aka UA9CLB) contest position (sorry all
the talks are in Russian). The tour includes almost all of the antennas and
2 x K3 set up in SO3R configuration.
Just thought it might be interesting for some of the reflector participants.

73, Igor UA9CDC

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Edward R Cole

Re: adding 250Hz filer, any improvement?

In reply to this post by Jorge Diez - CX6VM

Vic and all who replied,

I kind of cheated when I made my inquiry. I omitted the fact that I
was actually asking about copying eme CW (though some of you may have
guessed). I am the only station in Alaska that regularly operates
2m-eme. Since Alaska counts both for WAS and DXCC that makes me in demand.

I have not operated CW eme for a long time, but am about to start up
again (I have mainly operated digital eme since 2003). One of the
main reasons for my K3 purchase was operating CW eme. (I also use it
on 500-KHz)

In the past I was using my FT-847 which only has the 2.2-KHz SSB
filter. I used the DSP CW filter on 400-Hz for searching for signals
and then narrowed down to either 200 or 100-Hz (the FT-847 DSP is not
variable and provides only 400/200/100/25 Hz filtering). My hearing
is bad and I wear hearing aids full-time, so I can not dig out weak
signals as well as some. Narrowing bandpass is essential.

I have not tried to copy CW eme with the K3, yet. I am waiting for
my new DEMI 144/28 transverter. But I did experiment listening to
weak CW on 20m and tried out the APF feature. It works super! I am
looking forward to trying it out on eme.

This coming weekend is the annual 432 & 1296 SSB eme event (not
really a contest), so I am trying to get set up for that. There will
be both CW and SSB signals to listen to. Unfortunately, I found that
one of my FET's is bad in my 1296 amplifier so I will not be
transmitting. But it should be fun listening into all the
stations. I have a 1296/28 transverter to use with the K3.

73, Ed - KL7UW

------------------------------

Message: 11
Date: Wed, 09 Feb 2011 08:13:19 -0800
From: Vic K2VCO <[hidden email]>
Subject: Re: [Elecraft] adding 250Hz filer, any improvement?
To: [hidden email]
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

I see that others have told you that you can narrow the DSP and it
will be just as good as
long as there are no nearby signals greater than about S9+20.

Let me add that a huge improvement in copyability of weak CW can be
gained by using the
APF in current firmware. It has a bandwidth (I believe) of about 30
Hz at 6 dB points, and
also provides a slight gain boost. It's easiest to select 1 Hz tuning
steps (tab 'fine')
when tuning with it on.

I usually use a DSP bandwidth of 300-400 Hz and APF on when copying
really, really weak
signals.

I know there are guys like W4ZV who have a DSP between their ears
that does a better job
with wider bandwidths, but not all of us have this ability!

73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ 500 KHz - 10-GHz www.kl7uw.com
EME: 144-1.4kw*, 432-100w*, 1296-testing*, 3400-winter?
DUBUS Magazine USA Rep [hidden email]
======================================
*temp not in service
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