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K3 - Audio/IF filtering definitions

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Rick Stealey

K3 - Audio/IF filtering definitions

I'm confused as to the function of the receive equalization vs the width vs the hi
and low cut.

Example - The traditional SSB filter is, say, a 2.7 KHz wide filter with the
bfo carrier 300 hz from one side of the filter passband. This provides audio response
of 300 hz to (300+ 2700) = 3000 Hz.

So I can set my K3 to 2700 bandwidth and adjust the SHIFT control to give the
same response as above. But in addition I can adjust the 8 band receive EQ to roll
off or peak this spectrum, right? I assume this filtering is at audio, after the detector.

Then what are the hi cut and low cut front panel controls for? What do they control?

Rick K2XT

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N5GE-2

Re: K3 - Audio/IF filtering definitions

They keep you from having to go into Config to change equalizer for a
specific situation and they work with the RX signal directly.

Amateur Radio Operator N5GE
ARRL Lifetime Member
QCWA Lifetime Member

On Tue, 27 Nov 2012 22:16:16 +0000, Rick Stealey
<[hidden email]> wrote:

>
>I'm confused as to the function of the receive equalization vs the width vs the hi
>and low cut.
>
>Example - The traditional SSB filter is, say, a 2.7 KHz wide filter with the
>bfo carrier 300 hz from one side of the filter passband. This provides audio response
>of 300 hz to (300+ 2700) = 3000 Hz.
>
>So I can set my K3 to 2700 bandwidth and adjust the SHIFT control to give the
>same response as above. But in addition I can adjust the 8 band receive EQ to roll
>off or peak this spectrum, right? I assume this filtering is at audio, after the detector.
>
>Then what are the hi cut and low cut front panel controls for? What do they control?
>
>Rick K2XT
>
>______________________________________________________________
>Elecraft mailing list
>Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>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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Rick WA6NHC

Re: K3 - Audio/IF filtering definitions

The filter sets the rough bandwidth limits. Then you can shape the
resulting audio with the equalizer to your particular need.

You can also narrow the gross bandwidth with the width control and/or
re-center the bandpass with the shift control and/or narrow one edge of the
bandpass (at a time) with the high/low cut.

Think of the high/low cut as a gross equalizer, similar to the treble/bass
controls on an old stereo. They CUT above (for high cut) and below (for low
cut) at the threshold that you set.

This leaves you with several methods at your disposal to shape, enhance or
eliminate portions of the audio band so you have the best chance of getting
what you need from the signal.

And then on top of that, you also have a very effective notch filter.

73,
Rick wa6nhc

-----Original Message-----
From: Rick Stealey

>Then what are the hi cut and low cut front panel controls for? What do
they control?

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alorona

Re: K3 - Audio/IF filtering definitions

HI and LO cut controls determine the bandwidth, such as the 300 - 2700 Hz (2400
Hz bandwidth) in the example you provided.

That bandwidth is flat. However, you may elect to shape the bandwidth to
something other than flat, such as to boost the high frequencies, or cut the
dreaded "400 Hz bump" present in many signals , or something else. In that case,
the RX EQ is used to obtain a non-flat audio response. However, the cutoff
frequencies of 300 and 2700 are not affected in any significant way because HI
and LO set these limits.

Al W6LX

>Then what are the hi cut and low cut front panel controls for? What do
they control?
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Don Wilhelm-4

Re: K3 - Audio/IF filtering definitions

In reply to this post by Rick Stealey

Rick,

The Hi-Cut and Lo-Cut do essentially the same thing as Width and Shift,
but they make voice signals easier to deal with.

If you have played with Width and Shift on the K3 or other transceivers,
you will know that anytime you change the width control, you have to
also change the shift control to maintain intelligibility for the
received voice signal.

The main reason is that you must have some audio content in the 300 to
500 Hz range to have intelligibility in the human speech range. So if
you have your Width set at 2.7kHz and the Shift set at 1500 Hz, you will
be receiving 300 to 3000 Hz. Now move the width to 2.1kHz and the
passband changes to 600 to 2700 Hz, and you have lost much of the low
frequency content of the signal - changing the Shift control to a lower
frequency will recover that 300 to 500 Hz segment of the audio spectrum
that is essential to communications fidelity.

OK, the Hi-Cut and LoCut controls work in a similar manner as the Width
and Shift. HiCut reduces the high frequency content in the received
signal while not changing the low frequency end. That is ideal for
voice communications where the 300 to 500 Hz content must be preserved
for good intelligibility. Try an experiment - set LoCut at 300 Hz and
then tune in an SSB signal. Reduce HiCut until you can no longer
understand the vocal content. If my guess is correct, you will still be
able to understand the voice content when HiCut is at 1500 Hz (that is a
width of 1200 Hz).

Now try the same thing using Width and Shift - it will likely be
cumbersome to adjust both the Shift and Width to accomplish the same
1200 Hz width while keeping the 300 to 500 Hz content active with the
shift control.

So the result is to use Width and Shift for CW where the center
frequency is well defined, but on SSB (or other voice modes) the use of
HiCut and LoCut makes things a lot easier - set LoCut somewhere between
200 and 400 Hz and leave it there - HiCut can be reduced to remove high
audio frequency 'garbage' as desired. If you run into interfering
signals on the low audio frequency range, there is not much you can do
about it without reducing signal intelligibility (time to QSY).

73,
Don W3FPR

On 11/27/2012 5:16 PM, Rick Stealey wrote:

> I'm confused as to the function of the receive equalization vs the width vs the hi
> and low cut.
>
> Example - The traditional SSB filter is, say, a 2.7 KHz wide filter with the
> bfo carrier 300 hz from one side of the filter passband. This provides audio response
> of 300 hz to (300+ 2700) = 3000 Hz.
>
> So I can set my K3 to 2700 bandwidth and adjust the SHIFT control to give the
> same response as above. But in addition I can adjust the 8 band receive EQ to roll
> off or peak this spectrum, right? I assume this filtering is at audio, after the detector.
>
> Then what are the hi cut and low cut front panel controls for? What do they control?
>
> Rick K2XT
>

Don Wilhelm-4

Re: K3 - Audio/IF filtering definitions

In reply to this post by Rick WA6NHC

Rick,

Are you confusing HiCut/LoCut with the RX (or TX) EQ? There are no
bands to the HiCut or LoCut, just limits to the DSP produced passband.

73,
Don W3FPR

On 11/27/2012 5:37 PM, Rick Bates wrote:

> The filter sets the rough bandwidth limits. Then you can shape the
> resulting audio with the equalizer to your particular need.
>
> You can also narrow the gross bandwidth with the width control and/or
> re-center the bandpass with the shift control and/or narrow one edge of the
> bandpass (at a time) with the high/low cut.
>
> Think of the high/low cut as a gross equalizer, similar to the treble/bass
> controls on an old stereo. They CUT above (for high cut) and below (for low
> cut) at the threshold that you set.
>
> This leaves you with several methods at your disposal to shape, enhance or
> eliminate portions of the audio band so you have the best chance of getting
> what you need from the signal.
>
> And then on top of that, you also have a very effective notch filter.
>
> 73,
> Rick wa6nhc
>

Bill Frantz

Re: K3 - Audio/IF filtering definitions

In addition to the SSB examples several people have posted, the
Hi and Lo Cut controls are quite useful in soundcard digital
modes. For example, when I use my computer for PSK, I scan the
band with the bandwidth set to a low of 300 Hz and a high of
2.6KHz. I have a macro to set this bandwith (IS 1450;BW0230;).

When I start a QSO, I narrow the Hi and Lo Cut controls to
eliminate most of the other signals on my waterfall. The audio
frequency marks on the computer's waterfall make this adjustment
straight forward if a bit fiddly. The resulting bandwidth is
between 50Hz and 150Hz and makes use of the 250Hz crystal filter
in the K3. (Someday I have to reprogram the computer to send the
narrow bandwidth details to the K3.) With this narrow bandwidth
I find it easier to pull weak signals out of the noise floor and
avoid overload from nearby strong signals.

Cheers - Bill, AE6JV

-------------------------------------------------------------------------
Bill Frantz | Airline peanut bag: "Produced | Periwinkle
(408)356-8506 | in a facility that processes | 16345
Englewood Ave
www.pwpconsult.com | peanuts and other nuts." - Duh | Los Gatos,
CA 95032

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Rick WA6NHC

Re: K3 - Audio/IF filtering definitions

That's a key point as not everyone understands that less audio is better on
PSK and most folks tend to hit the audio hard on both TX and RX. The
resulting IMD is shown as 'echoes' on the waterfall and it tends to bang on
the soundcard AGC, potentially blocking the signal you want to hear.

For non-Elecraft gear, adjust to *just* when the ALC is starting to get
tickled, then back off a titch. For Elecraft, make the fifth ALC bar blink
(this changes with the actual tone used) and go no higher.

Of course you can use the data modes with the K(X)3 instead.

Rick wa6nhc

-----Original Message-----
From: Bill Frantz

With this narrow bandwidth
I find it easier to pull weak signals out of the noise floor and
avoid overload from nearby strong signals.

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Don Wilhelm-4

Re: K3 - Audio/IF filtering definitions

Rick,

What you say is true for the K3 and the KX3, but you referred to
"El;ecraft" as all encompassing == which includes the K2 as well.
One would adjust the K2 audio level to just indicate one ALC bar and
then back off until it doe not light.

On 11/27/2012 6:43 PM, Rick Bates wrote:

> That's a key point as not everyone understands that less audio is better on
> PSK and most folks tend to hit the audio hard on both TX and RX. The
> resulting IMD is shown as 'echoes' on the waterfall and it tends to bang on
> the soundcard AGC, potentially blocking the signal you want to hear.
>
> For non-Elecraft gear, adjust to *just* when the ALC is starting to get
> tickled, then back off a titch. For Elecraft, make the fifth ALC bar blink
> (this changes with the actual tone used) and go no higher.
>
> Of course you can use the data modes with the K(X)3 instead.
>
> Rick wa6nhc
>
> -----Original Message-----
> From: Bill Frantz
>
> With this narrow bandwidth
> I find it easier to pull weak signals out of the noise floor and
> avoid overload from nearby strong signals.
>
> ______________________________________________________________
> 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
>

Rick WA6NHC

Re: K3 - Audio/IF filtering definitions

Sorry about that. It shows my (lack of) experience with other than the K3.

Rick nhc

-----Original Message-----
From: Don Wilhelm

Rick,

What you say is true for the K3 and the KX3, but you referred to
"El;ecraft" as all encompassing == which includes the K2 as well.
One would adjust the K2 audio level to just indicate one ALC bar and
then back off until it doe not light.

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KD8NNU

Re: K3 - Audio/IF filtering definitions

In reply to this post by Bill Frantz

I have multiple macros for setting filter width for digital modes.

I use the HRD suite of software with the DM780. Basically I center the
selected signal with one mouse click and then pick the filter I want with
another mouse click and center point at 1.5 where I centered the RX
transmission. I can take PSK signals that are being masked by other other
signals in a wide waterfall to 599 copy. So I don’t have to care about
strong signals drowning out a weak signal I am trying to copy.

This is one of the great strong points of the K3 from my perspective with
the multiple filter options for different operating conditions.

~73
Don
KD8NNU
-.- -.. ---.. -. -. ..-
-----Original Message-----
From: Bill Frantz
Sent: Tuesday, November 27, 2012 6:25 PM
To: [hidden email]
Subject: Re: [Elecraft] K3 - Audio/IF filtering definitions

In addition to the SSB examples several people have posted, the
Hi and Lo Cut controls are quite useful in soundcard digital
modes. For example, when I use my computer for PSK, I scan the
band with the bandwidth set to a low of 300 Hz and a high of
2.6KHz. I have a macro to set this bandwith (IS 1450;BW0230;).

When I start a QSO, I narrow the Hi and Lo Cut controls to
eliminate most of the other signals on my waterfall. The audio
frequency marks on the computer's waterfall make this adjustment
straight forward if a bit fiddly. The resulting bandwidth is
between 50Hz and 150Hz and makes use of the 250Hz crystal filter
in the K3. (Someday I have to reprogram the computer to send the
narrow bandwidth details to the K3.) With this narrow bandwidth
I find it easier to pull weak signals out of the noise floor and
avoid overload from nearby strong signals.

Cheers - Bill, AE6JV

-------------------------------------------------------------------------
Bill Frantz | Airline peanut bag: "Produced | Periwinkle
(408)356-8506 | in a facility that processes | 16345
Englewood Ave
www.pwpconsult.com | peanuts and other nuts." - Duh | Los Gatos,
CA 95032

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