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K3 in WPX SSB with 2.7 roofer

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KM3K

Re: [K3] Roofing filters are misunderstood

There you go!
Well said.
73 Jerry KM3K KX3#6088
Sent from my NOOK

Don Wilhelm <[hidden email]> wrote:

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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David Gilbert

Re: [K3] Roofing filters are misunderstood

In reply to this post by Bill Turner-2

Roof -> upper ... higher ... overhead ... protective ...

There are several fairly intuitive possibilities, none of which are
worth getting confused about in the first place.

Dave AB7E

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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Bill Turner-2

Re: [K3] Roofing filters are misunderstood

In reply to this post by Josh Fiden

ORIGINAL MESSAGE: (may be snipped)

On 5/12/2014 12:38 PM, Josh Fiden wrote:
> "The term “roofing” stems from the fact that it protects the rest of
> the radio following it from out of the passband signals."

REPLY:

A roof keeps what falls on it (rain, snow) out. It doesn't pass it
through. Just the opposite of what a so-called roofing filter does.

I prefer names that are pretty much self-explanatory. This one isn't.

73, Bill W6WRT
[hidden email]
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Elecraft mailing list

Re: [K3] Roofing filters are misunderstood

In reply to this post by David Gilbert

Wasn't the chicken little sky is falling thing popular back when "roofing filter" originated? We may be luckier than we know that it became known as a roofing filter.

73 de Dennis KD7CAC
Scottsdale, AZ

On May 12, 2014, at 3:04 PM, David Gilbert <[hidden email]> wrote:

>
> Roof -> upper ... higher ... overhead ... protective ...
>
> There are several fairly intuitive possibilities, none of which are worth getting confused about in the first place.
>
> Dave AB7E
>
>
>
>
> 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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Nr4c

Re: [K3] Roofing filters are misunderstood

In reply to this post by Bill Turner-2

Think of your roof blocking the rain so the ceiling doesn't have to work so hard.

It's not used for band-pass, it's to let the DSP work less.

Sent from my iPhone
...nr4c. bill

> On May 12, 2014, at 3:01 PM, Bill Turner <[hidden email]> wrote:
>
> 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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David Gilbert

Re: [K3] Roofing filters are misunderstood

In reply to this post by Bill Turner-2

Actually, a roofing filter does exactly what it says. It protects
against ... i.e., does not allow to pass ... out-of-passband signals
from affecting the ADC or hardware AGC. It's a "roof" against unwanted
energy and a window for desired signals. So would you prefer to call it
a "window?" Have at it, but that doesn't alter the fact that its
fundamental purpose is to protect ... protect the ADC and protect the
AGC so that they can perform their function properly. And it doesn't
mean that anybody will recognize what you're talking about, which is
probably more relevant than the semantics involved.

Dave AB7E

On 5/12/2014 3:38 PM, Bill Turner wrote:

> ORIGINAL MESSAGE: (may be snipped)
>
> On 5/12/2014 12:38 PM, Josh Fiden wrote:
>> "The term “roofing” stems from the fact that it protects the rest of
>> the radio following it from out of the passband signals."
>
> REPLY:
>
> A roof keeps what falls on it (rain, snow) out. It doesn't pass it
> through. Just the opposite of what a so-called roofing filter does.
>
> I prefer names that are pretty much self-explanatory. This one isn't.
>
> 73, Bill W6WRT
> [hidden email]

wayne burdick

Roofing filters

Administrator

David Gilbert <[hidden email]> wrote:

> Actually, a roofing filter does exactly what it says. It protects against ... i.e., does not allow to pass ... out-of-passband signals from affecting the ADC or hardware AGC. It's a "roof" against unwanted energy and a window for desired signals. So would you prefer to call it a "window?" Have at it, but that doesn't alter the fact that its fundamental purpose is to protect ... protect the ADC and protect the AGC so that they can perform their function properly. And it doesn't mean that anybody will recognize what you're talking about, which is probably more relevant than the semantics involved.

In receive I.F. applications, a crystal filter is used as a very narrow (very high-Q) band-pass filter. It cuts off unwanted signals above and below the desired passband. In a modern superhet like the K3, the crystal filter augments the DSP in a subsequent I.F., providing improved ultimate rejection and steeper skirts.

In some implementations you can slide the I.F. associated with the crystal filter to the left or right of the nominal receive passband, so that the filter acts, in effect, like a low-pass or high-pass filter, working against the center frequency of later IFs. This can be useful in protecting the downstream I.F. on one side, but not the other. Narrow filtering takes care of both ends.

Radios that don't use hardware roofing filters of some kind typically have worse blocking dynamic range (BDR) than those that do. For example, the K3 has typical BDR of over 140 dB, 15 to 20 dB better than radios with no hardware filtering (i.e., pure SDRs). This is why a K3 outfitted with narrow filters works well for contesting, Field Day, and DXpeditions; it won't get desensed by either the wide- or narrow-spaced onslaught often experienced in these situations.

73,
Wayne
N6KR

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gdaught6

Re: [K3] Roofing

In reply to this post by David Gilbert

OK, apologies in advance for killing this thread, but I can't resist!

> There are several fairly intuitive possibilities, none of which are
> worth getting confused about in the first place.

A fellow and his dog walk into a bar. The fellow asks the bartender "If my talking
dog answers a question correctly, will you give me a beer?"

Bartender: "Talking dog, eh? Sure."

Fellow: "What is the exterior upper covering of a building?"

Dog: "Roof!"

Beer delivered...

Fellow: "What is the texture of sandpaper?"

Dog: "Ruff!"

another beer...

Fellow: "What is the first IF filter in a K3?"

Dog: "Roof!"

another beer...

Fellow: "Who was the greatest home run hitter in baseball?"

Dog: "Roof!"

The bartender tires of the game and quite forcefully throws the fellow and his dog out
on the sidewalk.

As the fellow gets up and brushes himself off, the dog says

"DiMaggio? Maris? Aaron?"

Sorry, es vy 73,

George T Daughters, K6GT
CU in the California QSO Party (CQP)
October 4-5, 2014

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Bill Turner-2

Re: [K3] Roofing filters are misunderstood

In reply to this post by David Gilbert

ORIGINAL MESSAGE: (may be snipped)

On 5/12/2014 4:15 PM, David Gilbert wrote:
> So would you prefer to call it a "window?"

REPLY:

I like that! Much more accurate. A roof keeps everything out while a
window lets only certain things such as the desired signal in.

Much more self-explanatory.

73, Bill W6WRT
[hidden email]
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Frank Precissi

Re: [K3] Roofing filters are misunderstood

On Mon, May 12, 2014 at 8:47 PM, Bill Turner <[hidden email]> wrote:

> I like that! Much more accurate. A roof keeps everything out while a
> window lets only certain things such as the desired signal in.
>
> Much more self-explanatory.
>

Should rename them to skylight filters.. :) Holes in the roof to let stuff
through.

Frank
KG6EYC
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KM3K

Re: [K3] Roofing filters are misunderstood

In reply to this post by Dave Hachadorian-2

That's a good name.
I like it.
73 Jerry KM3K
Sent from my NOOK

Frank Precissi <[hidden email]> wrote:

On Mon, May 12, 2014 at 8:47 PM, Bill Turner <[hidden email]> wrote:

> I like that! Much more accurate. A roof keeps everything out while a
> window lets only certain things such as the desired signal in.
>
> Much more self-explanatory.
>

Should rename them to skylight filters.. :) Holes in the roof to let stuff
through.

Frank
KG6EYC
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