K3 in WPX SSB with 2.7 roofer

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Re: [K3] Roofing filters are misunderstood

k6dgw
I too think roofing filters are really not well understood.  For the
record, I have the stock SSB [2.7 KHz? I don't actually know] and the
500 Hz CW.  In 99% of my operating situations, it doesn't matter which
one I use, I set the received BW with the DSP, and I'm a very happy ham.

I do have several close HP contesters, WX6V is one.  On CW if I were to
use the 2.7 roofer, even with a 250 Hz DSP, Jim will desense my K3 --
like maybe 1.5 miles as the electromagnetic waves travel.  The roofer
makes a difference with strong close in signals.  Whether or not you
want a 1.8, 2.7, 5-pole, 8-pole, or whatever may be trying to pick fly
poop out of the pepper for most of us.  If you run a lot of CW in
crowded conditions, a more CW-ish filter is likely good for you.

My neighbor Jim got a K3 early this year, replacing an ICOM<something>.
  Still just as strong on frequency, all of the phase noise has
disappeared, no clicks -- nothing.  Yet again, I'm a happy ham.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2014 Cal QSO Party 4-5 Oct 2014
- www.cqp.org

On 5/11/2014 7:02 PM, David Gilbert wrote:
>
> I completely agree with all of that except for the very last sentence.
> Clearly you've never used a 756Pro (first version) in a major CW
> contest.  I can remember very loud stations 10 or 15 KHz away completely
> desensing my receiver to the point that the station I was trying to copy
> simply disappeared.  When I switched to the K3 the difference was
> astounding.


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Re: [K3] Roofing filters are misunderstood

Joe Subich, W4TV-4
In reply to this post by David Gilbert

> I can remember very loud stations 10 or 15 KHz away completely
> desensing my receiver to the point that the station I was trying to
> copy simply disappeared. When I switched to the K3 the difference
> was astounding.

That is because the 756Pro is a completely brain dead design ... there
is only a single 30 KHz or so roofing filter at VHF and AGC which is
based on total signal in that 30 KHz or so "window" starts at a very
low level.  The only job of the K3's *hardware AGC* is to protect the
analog to digital converter from being driven into saturation so it
does not begin to activate until approximately S9+40.

The K3's normal AGC is entirely DSP based and is effectively
controlled by only the signal which passes through the DSP (it is
a shame the AGC control point isn't also after the notch <G>).

73,

    ... Joe, W4TV


On 5/11/2014 10:02 PM, David Gilbert wrote:

>
> I completely agree with all of that except for the very last sentence.
> Clearly you've never used a 756Pro (first version) in a major CW
> contest.  I can remember very loud stations 10 or 15 KHz away completely
> desensing my receiver to the point that the station I was trying to copy
> simply disappeared.  When I switched to the K3 the difference was
> astounding.
>
> 73,
> Dave   AB7E
>
>
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Re: [K3] Roofing filters are misunderstood

Jack Brindle-2
In reply to this post by alorona
I would take issue with your answer to #1. It really depends on your situation. For most of the folks on this list your answer very well may be correct. In areas where there is very high station density, it probably is not. Here in Silicon Valley there are a LOT of very strong near-by signals. The 1.8 KHz filter keeps close-in LOUD signals out of my passband so that the DSP filters have a chance to do their job. This is the whole purpose of the filter, to keep other strong signals out of the passband so that the DSP can do the real work.

By the way, for contesting (actually my main operating mode), I normally listen to SSB signals with low cut at 500 and high cut in the 1500-1800 range, well inside the 1.8KHz filter’s purview. Interestingly, I use matched 500 Hz 5-pole filters for CW contesting, where I can get within just a few hundred hertz of the local big signals without problem. My normal DSP bandwidth is something less that 500 Hz. It’s sideband contesting where I need the narrow filters. Since most of the local big guns also use K3s, phase noise and other similar problems are not a factor here. I really can get close to these folks and work lots of stations without either one of us being disturbed. I credit all this to the great RF system my friends have created.

When I’m not in one of the big contests, or just casual QSOs where the big guns aren’t a factor, the 2.7 KHz filter does an outstanding job on whatever mode I use.

I guess there is an exception to everything, and indeed there are times when the narrow filters are needed. Some of us actually do fall in that category. Oh to live back in the south where I definitely didn't have the problem…

Jack B, W6FB (ex-WA4FIB)


On May 11, 2014, at 2:03 PM, Al Lorona <[hidden email]> wrote:

> What determines the bandwidth you hear at the loudspeaker? It's not your roofing filter, despite a continuing notion that it is.
>  
> Dave Hachadorian's point in a post a few weeks ago was that you don't need a 1.8 kHz filter to get a 1.8 kHz bandwidth. You're free to set whatever bandwidth you want with any filter.
>
> Before rigs had DSP we got used to the idea that your crystal filter sets your bandwidth. That's not true any more. It sets your *maximum* bandwidth. You then have the freedom to narrow and position a bandwidth arbitrarily using the DSP controls [SHIFT and WIDTH or HI and LO].
>
>
> Here's a true-false quiz:
>
>  
> 1. I'm a contester, so I need a 1.8 kHz roofing filter in the K3.
>  
> 2. I should purchase the 400 Hz filter if I like to operate CW with bandwidths of 300 - 400 Hz.
>  
> 3. For SSB, the 2.7 and 2.8 kHz filters are 'too wide'.
>  
> 4. I have the 2.7 kHz filter installed, so for best results I should set my WIDTH control for a passband of 2.7 kHz.
>  
> 5. I can use my 2.7 kHz filter in CW mode with my LO=0.30 and HI=0.50 (that is, BW=0.20).
>  
>  
> The answers are:
>  
> 1. False. You do not need a 1.8 kHz filter just to set the BW=1.80. A 2.7 kHz filter can serve well during a contest with a much narrower DSP bandwidth. Refer to Dave's original post.
> 2. False. You can set the CW bandwidth to 400 using any filter whose bandwidth is equal to or greater than 400.
> 3. False. This was Dave's point. You're free to have a 2.7 or 2.8 installed, yet set the WIDTH to 1.8, 1.5 or anything else you wish.
> 4. False. You don't need to restrict yourself to only that bandwidth. You can set it to a narrower value if you wish.
> 5. True. And you'll probably suffer no ill effects under most conditions.
>  
> Furthermore, the "but extremely strong signals will pump my hardware AGC" arguments are probably a bit overrated. Most folks, even before a strong station gets close enough to do that, will give up and leave the frequency because of the QRM, especially in the presence of transmitted phase noise or key clicks as has come up in more recent posts.
>
> So then why have narrow roofing filters to choose from? To maximize the close-in dynamic range, which is important if you have large antennas in high-RF environments.
>  
> The vast majority of hams does not absolutely need really narrow roofing filters. It's wonderful that the K3 allows this, but it's certainly not mandatory, especially for casual operating.
>  
> Finally, note that if you received good training as a Novice with a poor, unselective receiver, you'll be able to copy right through any AGC pumping! It's the operator, more than the filters.
>
>  
> Al  W6LX
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Re: [K3] Roofing filters are misunderstood

Bill Turner-2
In reply to this post by k6dgw
ORIGINAL MESSAGE:          (may be snipped)

On 5/11/2014 7:25 PM, Fred Jensen wrote:
> I too think roofing filters are really not well understood.

REPLY:

A large part of the misunderstanding is due to the name. Whoever chose
the name "roofing" did a great disservice. A better name would simply be
it's function:  1st I.F. filter.

That's what it is and that's what it does.

I have always thought that "roofing" was a marketing ploy to imbue it
with some kind of magical powers.

73, Bill W6WRT

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Re: [K3] Roofing filters are misunderstood

NK7Z
On Sun, 2014-05-11 at 22:06 -0700, Bill Turner wrote:

"I have always thought that "roofing" was a marketing ploy to imbue it
with some kind of magical powers."

Bill,
"These aren't the filters you are looking for...  Move along..."

Sorry, I just had too inject that at this point in the discussion!  It
just seemed too funny not to...

To get back on topic,

As soon as someone here said they are 1st IF filters, all questions
about them were answered...  THANK YOU whoever said that.

--
Thanks and 73's,
For equipment, and software setups and reviews see:
www.nk7z.net
for MixW support see;
http://groups.yahoo.com/neo/groups/mixw/info
for Dopplergram information see:
http://groups.yahoo.com/neo/groups/dopplergram/info
for MM-SSTV see:
http://groups.yahoo.com/neo/groups/MM-SSTV/info




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Re: [K3] Roofing filters are misunderstood

Charlie T, K3ICH
Good point.  A true roofing filter would be in the antenna line.

Repeaters have "roofing" filters, typically in the form of an extremely high
Q resonant cavity.

Chas
----- Original Message -----
From: "David Cole" <[hidden email]>
To: <[hidden email]>
Sent: Monday, May 12, 2014 8:43 AM
Subject: Re: [Elecraft] [K3] Roofing filters are misunderstood


> On Sun, 2014-05-11 at 22:06 -0700, Bill Turner wrote:
>
> "I have always thought that "roofing" was a marketing ploy to imbue it
> with some kind of magical powers."
>
> Bill,
> "These aren't the filters you are looking for...  Move along..."
>
> Sorry, I just had too inject that at this point in the discussion!  It
> just seemed too funny not to...
>
> To get back on topic,
>
> As soon as someone here said they are 1st IF filters, all questions
> about them were answered...  THANK YOU whoever said that.
>
>

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Re: [K3] Roofing filters are misunderstood

Arie Kleingeld PA3A-2
In reply to this post by alorona
Well,

You defenitely need those filters in the K3.
When signals are strong and the band is busy, signals coming through the
roofing filter (line S9+20dB) is said to pump the hardware AGC, even if
you have the DSP filtering set to a small BW. Anyway, you can certainly
hear that.
Try it on CW,  on 40m in the evening when there's a contest. You'll love
the 400Hz roofing filter.


73
Arie PA3A




Al Lorona schreef op 11-5-2014 23:03:

> What determines the bandwidth you hear at the loudspeaker? It's not your roofing filter, despite a continuing notion that it is.
>  
> Dave Hachadorian's point in a post a few weeks ago was that you don't need a 1.8 kHz filter to get a 1.8 kHz bandwidth. You're free to set whatever bandwidth you want with any filter.
>
> Before rigs had DSP we got used to the idea that your crystal filter sets your bandwidth. That's not true any more. It sets your *maximum* bandwidth. You then have the freedom to narrow and position a bandwidth arbitrarily using the DSP controls [SHIFT and WIDTH or HI and LO].
>
>
> Here's a true-false quiz:
>
>  
> 1. I'm a contester, so I need a 1.8 kHz roofing filter in the K3.
>  
> 2. I should purchase the 400 Hz filter if I like to operate CW with bandwidths of 300 - 400 Hz.
>  
> 3. For SSB, the 2.7 and 2.8 kHz filters are 'too wide'.
>  
> 4. I have the 2.7 kHz filter installed, so for best results I should set my WIDTH control for a passband of 2.7 kHz.
>  
> 5. I can use my 2.7 kHz filter in CW mode with my LO=0.30 and HI=0.50 (that is, BW=0.20).
>  
>

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Re: [K3] Roofing filters are misunderstood

KM3K
In reply to this post by Bill Turner-2
Hello Bill,
The term "roofing-filter" made sense back in the 1980's when I designed
roofing-filters at 70 MHz.
Bandwidths would be in tens of KHz.
The purpose then was to protect downstream circuitry by rejecting very
strong out-of-band signals that could cause overload; selectivity was not
the purpose.
Selectivity was done further downstream.
So the term has become corrupted over the years.
73 Jerry KM3K


-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of Bill
Turner
Sent: Monday, May 12, 2014 1:07 AM
To: [hidden email]
Subject: Re: [Elecraft] [K3] Roofing filters are misunderstood

ORIGINAL MESSAGE:          (may be snipped)

On 5/11/2014 7:25 PM, Fred Jensen wrote:
> I too think roofing filters are really not well understood.

REPLY:

A large part of the misunderstanding is due to the name. Whoever chose
the name "roofing" did a great disservice. A better name would simply be
it's function:  1st I.F. filter.

That's what it is and that's what it does.

I have always thought that "roofing" was a marketing ploy to imbue it
with some kind of magical powers.

73, Bill W6WRT

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Re: [K3] Roofing filters are misunderstood

Jack Brindle-2
Jerry,

Why do you say it has been corrupted? This is exactly the purpose for the Roofing Filters in the K3.

Jack B, W6FB


On May 12, 2014, at 9:33 AM, Jerome Sodus <[hidden email]> wrote:

> Hello Bill,
> The term "roofing-filter" made sense back in the 1980's when I designed
> roofing-filters at 70 MHz.
> Bandwidths would be in tens of KHz.
> The purpose then was to protect downstream circuitry by rejecting very
> strong out-of-band signals that could cause overload; selectivity was not
> the purpose.
> Selectivity was done further downstream.
> So the term has become corrupted over the years.
> 73 Jerry KM3K
>
>
> -----Original Message-----
> From: Elecraft [mailto:[hidden email]] On Behalf Of Bill
> Turner
> Sent: Monday, May 12, 2014 1:07 AM
> To: [hidden email]
> Subject: Re: [Elecraft] [K3] Roofing filters are misunderstood
>
> ORIGINAL MESSAGE:          (may be snipped)
>
> On 5/11/2014 7:25 PM, Fred Jensen wrote:
>> I too think roofing filters are really not well understood.
>
> REPLY:
>
> A large part of the misunderstanding is due to the name. Whoever chose
> the name "roofing" did a great disservice. A better name would simply be
> it's function:  1st I.F. filter.
>
> That's what it is and that's what it does.
>
> I have always thought that "roofing" was a marketing ploy to imbue it
> with some kind of magical powers.
>
> 73, Bill W6WRT
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
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>
> This list hosted by: http://www.qsl.net
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> Message delivered to [hidden email]
>
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Re: [K3] Roofing filters are misunderstood

Greg - AB7R
http://www.elecraft.com/K3/Roofing_Filters.htm




On Mon, May 12, 2014 at 9:45 AM, Jack Brindle <[hidden email]> wrote:

> Jerry,
>
> Why do you say it has been corrupted? This is exactly the purpose for the
> Roofing Filters in the K3.
>
> Jack B, W6FB
>
>
> On May 12, 2014, at 9:33 AM, Jerome Sodus <[hidden email]> wrote:
>
> > Hello Bill,
> > The term "roofing-filter" made sense back in the 1980's when I designed
> > roofing-filters at 70 MHz.
> > Bandwidths would be in tens of KHz.
> > The purpose then was to protect downstream circuitry by rejecting very
> > strong out-of-band signals that could cause overload; selectivity was not
> > the purpose.
> > Selectivity was done further downstream.
> > So the term has become corrupted over the years.
> > 73 Jerry KM3K
> >
> >
> > -----Original Message-----
> > From: Elecraft [mailto:[hidden email]] On Behalf Of
> Bill
> > Turner
> > Sent: Monday, May 12, 2014 1:07 AM
> > To: [hidden email]
> > Subject: Re: [Elecraft] [K3] Roofing filters are misunderstood
> >
> > ORIGINAL MESSAGE:          (may be snipped)
> >
> > On 5/11/2014 7:25 PM, Fred Jensen wrote:
> >> I too think roofing filters are really not well understood.
> >
> > REPLY:
> >
> > A large part of the misunderstanding is due to the name. Whoever chose
> > the name "roofing" did a great disservice. A better name would simply be
> > it's function:  1st I.F. filter.
> >
> > That's what it is and that's what it does.
> >
> > I have always thought that "roofing" was a marketing ploy to imbue it
> > with some kind of magical powers.
> >
> > 73, Bill W6WRT
> >
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> > Message delivered to [hidden email]
> >
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> > Post: mailto:[hidden email]
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Re: [K3] Roofing filters are misunderstood

Don Wilhelm-4
In reply to this post by KM3K
Jerry,

Yes, the term has become corrupted and misunderstood over the years.

That *is* exactly what the K3 filters do (protect the downstream
circuits from strong out of passband signals), but is done using a much
more narrow bandwidth at the 1st IF.

If the operator never encounters signal levels in excess of S-9+30,
there is no need for the roofing filter, but signals stronger than that
are encountered commonly in contests and tuning through a DX pileup.

If it were not for the Hardware AGC, they would overload the A-D
converter causing the entire output to become garbage.
With the Hardware AGC present, that is not going to happen, but strong
signals within the 1st IF bandpass will cause "pumping" of the Hardware
AGC as those signals come and go.  In the K3, *that* condition is what
the roofing filters will prevent.

Bottom line, if you hear that "pumping" (and subsequent desensing of the
receiver), you would benefit from a more narrow filter.

73,
Don W3FPR

On 5/12/2014 12:33 PM, Jerome Sodus wrote:

> Hello Bill,
> The term "roofing-filter" made sense back in the 1980's when I designed
> roofing-filters at 70 MHz.
> Bandwidths would be in tens of KHz.
> The purpose then was to protect downstream circuitry by rejecting very
> strong out-of-band signals that could cause overload; selectivity was not
> the purpose.
> Selectivity was done further downstream.
> So the term has become corrupted over the years.
>

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Re: [K3] Roofing filters are misunderstood

KM3K
In reply to this post by Greg - AB7R
Thank-you, Greg.

Excellent.

Jerry KM3K

 

  _____  

From: Greg [mailto:[hidden email]]
Sent: Monday, May 12, 2014 12:52 PM
To: Jack Brindle
Cc: Jerome Sodus; [hidden email]
Subject: Re: [Elecraft] [K3] Roofing filters are misunderstood

 

http://www.elecraft.com/K3/Roofing_Filters.htm

 



 

On Mon, May 12, 2014 at 9:45 AM, Jack Brindle <[hidden email]> wrote:

Jerry,

Why do you say it has been corrupted? This is exactly the purpose for the
Roofing Filters in the K3.

Jack B, W6FB


On May 12, 2014, at 9:33 AM, Jerome Sodus <[hidden email]> wrote:

> Hello Bill,
> The term "roofing-filter" made sense back in the 1980's when I designed
> roofing-filters at 70 MHz.
> Bandwidths would be in tens of KHz.
> The purpose then was to protect downstream circuitry by rejecting very
> strong out-of-band signals that could cause overload; selectivity was not
> the purpose.
> Selectivity was done further downstream.
> So the term has become corrupted over the years.
> 73 Jerry KM3K

 

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Re: [K3] Roofing filters are misunderstood

Greg - AB7R
No problem Jerry.  Didn't seem to make much sense hashing out something
that was already clarified by the designers. :)

73
Greg



On Mon, May 12, 2014 at 9:59 AM, Jerome Sodus <[hidden email]> wrote:

>   Thank-you, Greg.
>
> Excellent.
>
> Jerry KM3K
>
>
>  ------------------------------
>
> *From:* Greg [mailto:[hidden email]]
> *Sent:* Monday, May 12, 2014 12:52 PM
> *To:* Jack Brindle
> *Cc:* Jerome Sodus; [hidden email]
>
> *Subject:* Re: [Elecraft] [K3] Roofing filters are misunderstood
>
>
>
> http://www.elecraft.com/K3/Roofing_Filters.htm
>
>
>
>
>
>
>
> On Mon, May 12, 2014 at 9:45 AM, Jack Brindle <[hidden email]> wrote:
>
> Jerry,
>
> Why do you say it has been corrupted? This is exactly the purpose for the
> Roofing Filters in the K3.
>
> Jack B, W6FB
>
>
> On May 12, 2014, at 9:33 AM, Jerome Sodus <[hidden email]> wrote:
>
> > Hello Bill,
> > The term "roofing-filter" made sense back in the 1980's when I designed
> > roofing-filters at 70 MHz.
> > Bandwidths would be in tens of KHz.
> > The purpose then was to protect downstream circuitry by rejecting very
> > strong out-of-band signals that could cause overload; selectivity was not
> > the purpose.
> > Selectivity was done further downstream.
> > So the term has become corrupted over the years.
> > 73 Jerry KM3K
>
>
>
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Re: [K3] Roofing filters are misunderstood

HP
In reply to this post by Don Wilhelm-4
I have two big time dxers/contesters near me - on 160 ,  one is -8 to -9 dBm
and the other is -10 to -11dBm . Folks , thats in the 50 to 100 mv area  at
the poor K3 .(S9+60 to 70 area)  Just for fun of it , I can easily see both
on my scope hung on my antenna.

With the 250 hz  8 pole - I could copy an HS0 at my noise level split 2.2
khz away from the -9 dBm station and  not even know he was there except
seeing him on the P3. (He is using a K3 exciter and an ALPHA amp. )

Cannot say that for some of the other locals who have phase noise from
various and sundry other rigs.

73 Hank K7HP

(SNIP)
If the operator never encounters signal levels in excess of S-9+30,
there is no need for the roofing filter, but signals stronger than that
are encountered commonly in contests and tuning through a DX pileup.

If it were not for the Hardware AGC, they would overload the A-D
converter causing the entire output to become garbage.
With the Hardware AGC present, that is not going to happen, but strong
signals within the 1st IF bandpass will cause "pumping" of the Hardware
AGC as those signals come and go.  In the K3, *that* condition is what
the roofing filters will prevent.

Bottom line, if you hear that "pumping" (and subsequent desensing of the
receiver), you would benefit from a more narrow filter.


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Re: [K3] Roofing filters are misunderstood

Bill Turner-2
In reply to this post by KM3K
ORIGINAL MESSAGE:          (may be snipped)

On 5/12/2014 9:33 AM, Jerome Sodus wrote:

> Hello Bill,
> The term "roofing-filter" made sense back in the 1980's when I designed
> roofing-filters at 70 MHz.
> Bandwidths would be in tens of KHz.
> The purpose then was to protect downstream circuitry by rejecting very
> strong out-of-band signals that could cause overload; selectivity was not
> the purpose.
> Selectivity was done further downstream.
> So the term has become corrupted over the years.
> 73 Jerry KM3K

REPLY:

I still don't get it. What does the word "roof" have to do with
bandpass? That's where the confusion comes from.

73, Bill W6WRT
[hidden email]
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Re: [K3] Roofing filters are misunderstood

Phil Wheeler-2
In reply to this post by Arie Kleingeld PA3A-2
At least I do, Arie. Maybe those with fewer
"local" signals do not.  Dunno.

Phil w7ox

On 5/12/14, 9:23 AM, Arie Kleingeld PA3A wrote:

> Well,
>
> You defenitely need those filters in the K3.
> When signals are strong and the band is busy,
> signals coming through the roofing filter (line
> S9+20dB) is said to pump the hardware AGC, even
> if you have the DSP filtering set to a small BW.
> Anyway, you can certainly hear that.
> Try it on CW,  on 40m in the evening when
> there's a contest. You'll love the 400Hz roofing
> filter.
>
>
> 73
> Arie PA3A
>
>
>
>
> Al Lorona schreef op 11-5-2014 23:03:
>> What determines the bandwidth you hear at the
>> loudspeaker? It's not your roofing filter,
>> despite a continuing notion that it is.
>>   Dave Hachadorian's point in a post a few
>> weeks ago was that you don't need a 1.8 kHz
>> filter to get a 1.8 kHz bandwidth. You're free
>> to set whatever bandwidth you want with any
>> filter.
>>
>> Before rigs had DSP we got used to the idea
>> that your crystal filter sets your bandwidth.
>> That's not true any more. It sets your
>> *maximum* bandwidth. You then have the freedom
>> to narrow and position a bandwidth arbitrarily
>> using the DSP controls [SHIFT and WIDTH or HI
>> and LO].
>>
>>
>> Here's a true-false quiz:
>>
>>   1. I'm a contester, so I need a 1.8 kHz
>> roofing filter in the K3.
>>   2. I should purchase the 400 Hz filter if I
>> like to operate CW with bandwidths of 300 - 400
>> Hz.
>>   3. For SSB, the 2.7 and 2.8 kHz filters are
>> 'too wide'.
>>   4. I have the 2.7 kHz filter installed, so
>> for best results I should set my WIDTH control
>> for a passband of 2.7 kHz.
>>   5. I can use my 2.7 kHz filter in CW mode
>> with my LO=0.30 and HI=0.50 (that is, BW=0.20).

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Re: [K3] Roofing filters are misunderstood

Josh Fiden
In reply to this post by Bill Turner-2
 From an older Inrad writeup (and consistent with Wayne's):

"The term “roofing” stems from the fact that it protects the rest of the
radio following it from out of the passband signals."

http://www.qth.com/inrad/roofing-filters.pdf

I like the term "preselector" from my 75S-1, but that doesn't fit well
with selectable bandwidths.

73,
Josh W6XU

On 5/12/2014 12:01 PM, Bill Turner wrote:
> I still don't get it. What does the word "roof" have to do with
> bandpass? That's where the confusion comes from.

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Re: [K3] Roofing filters are misunderstood

k6dgw
In reply to this post by Bill Turner-2
I have imperfect recollections that the source of the term "roofing
filter" came from the idea that the filter put a "roof" over your
receiver to prevent very strong, off-frequency signals from getting in.
  You'll need to crank up your imagination here ... similar to the roof
of your house keeping out things falling from the sky while desired
things can still enter through the doors.  I did say "imagination." :-)

I do also agree, it's probably not a particularly descriptive name, but
the filters do have a purpose in SDR's like the K3.  I think most of the
thread was aimed at the differences between the various filters
available for the K3.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2014 Cal QSO Party 4-5 Oct 2014
- www.cqp.org

On 5/12/2014 12:01 PM, Bill Turner wrote:

> I still don't get it. What does the word "roof" have to do with
> bandpass? That's where the confusion comes from.
>
> 73, Bill W6WRT
> [hidden email]


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Re: [K3] Roofing filters are misunderstood

Peter g3smt
In reply to this post by Dave Hachadorian-2
Bill,

Originally the superhet receivers converted from the signal frequency to
a lower fixed intermediate frequency in order to obtain sufficient
selectivity.  IFs went as low as 85kHz until crystal filters became more
widespread.  As designs changed ( changed not improved) it became usual
to convert to a higher frequency, in the order of 70MHz to obtain good
image rejection because manufacturers economised on signal frequency
filtering and they then down converted to a low IF as before.  To
protect the second mixer a roofing filter was added and so termed
because it was at the high IF ie the roof in terms of frequency.  There
were good reasons for this in commercial equipment and the amateur
equipment followed as a marketing ploy.  Hope that helps and please
excuse my poor writing.

Regards

Peter

G3SMT


> I still don't get it. What does the word "roof" have to do with
> bandpass? That's where the confusion comes from.
>
> 73, Bill W6WRT
> [hidden email]
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Re: [K3] Roofing filters are misunderstood

Don Wilhelm-4
In reply to this post by Bill Turner-2
Bill,

Like a roof protects the contents of a building, a roofing filter
protects the electronics that follow it from overload.

73,
Don W3FPR

On 5/12/2014 3:01 PM, Bill Turner wrote:
>
>
> I still don't get it. What does the word "roof" have to do with
> bandpass? That's where the confusion comes from.
>

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