K3 transmit and receive audio response

[AMFMTV]

Hello everyone,

I had a chance at Dayton this year to chat with the Elecraft honchos,
and had every one of my K3 questions answered.  Thanks, gentlemen.

Meanwhile, a few hours ago, Wayne had written:

{While I'm on this topic, I'd also like to suggest using a minimum of
both RX and TX EQ. The '0' levels were carefully determined
empirically, and in most cases the optimal values will be well below
the maximum range provided. Unless you have an aural sensitivity issue
in some pitch range, or a serious mic deficiency, I'd stay between +/-
6 dB. As with filter gain settings, excessive values can result in
adverse interaction with the DSP.}

What I would like to know is just what the ACTUAL response curves of
the K3 transmit and receive audio are (when all EQ settings are set to
'0', since Wayne stated: "The '0' levels were carefully determined
empirically."  It would appear from this statement that setting the
EQ's to '0' wouldn't necessarily result in a 'flat' response.

I design parameters for some broadcast audio processors (Omnia's)
and just am curious (and picky) what 'flat' actually is when the EQ's
in the K3 are all set to '0'.  And,  for transmit, is the internal RF
speech processor applied "pre" or "post" of the frequency response
shaping circuitry?

Thanks & 73.
Ted  W8IXY


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[KK7P]

> What I would like to know is just what the ACTUAL response curves of
> the K3 transmit and receive audio are (when all EQ settings are set to
> '0',

Flat means the EQ does not add or subtract to the filter response dialed
in by the operator with the SHIFT/WIDTH/HIGH CUT/LOW CUT controls.  The
high end and low end response will be dictated by those settings,  This
will be modified by the impedances in the path from the radio to the
headphones or speaker and the impedance of the headphones or speaker, or
the characteristics of the transformers and the overall impedances in
the LINE OUT case.

Finally, the edges of the selected passband will be rolled off by the
action of the FIR filter windowing function applied to the filter
coefficients.

73,

Lyle KK7P

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[KK7P]

> ...And,  for transmit, is the internal RF
> speech processor applied "pre" or "post" of the frequency response
> shaping circuitry?

Frequency shaping (Tx EQ) is done at audio, speech processing is done at
I.F.

73,

Lyle KK7P

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[Barry N1EU]

The low end response of the stock K3 is limited by coupling capacitor impedance in the audio stage.

73,
Barry N1EU

Lyle Johnson wrote

> What I would like to know is just what the ACTUAL response curves of
> the K3 transmit and receive audio are (when all EQ settings are set to
> '0',

Flat means the EQ does not add or subtract to the filter response dialed
in by the operator with the SHIFT/WIDTH/HIGH CUT/LOW CUT controls.  The
high end and low end response will be dictated by those settings,  This
will be modified by the impedances in the path from the radio to the
headphones or speaker and the impedance of the headphones or speaker, or
the characteristics of the transformers and the overall impedances in
the LINE OUT case.

Finally, the edges of the selected passband will be rolled off by the
action of the FIR filter windowing function applied to the filter
coefficients.

73,

Lyle KK7P

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[Joe Subich, W4TV-4]

> The low end response of the stock K3 is limited by coupling
> capacitor impedance in the audio stage.

Only in regard to the headphone amplifier when used with low
impedance (8 Ohm) headphones.  With the stock 10 uF caps the
-3dB point (corner frequency) for 8 Ohm headphones is 2 KHz.  
However, with professional (600 Ohms) headphones the corner
frequency is 25 Hz and with a Heil Proset (200 Ohms) the corner
frequency is 80 Hz.  

For reference, the corner frequency (-3 dB) of the speaker
amplifier using the stock coupling capacitors is about 17 Hz.
The audio response of speakers will be much more heavily
influenced by the speaker enclosure than the coupling caps
in the stock audio amplifier.

73,

   ... Joe, W4TV
 

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Barry N1EU
> Sent: Wednesday, June 17, 2009 8:13 AM
> To: [hidden email]
> Subject: Re: [Elecraft] K3 transmit and receive audio response
>
>
>
> The low end response of the stock K3 is limited by coupling
> capacitor impedance in the audio stage.
>
> 73,
> Barry N1EU
>
>
>
> Lyle Johnson wrote:
> >
> >> What I would like to know is just what the ACTUAL response
> curves of
> >> the K3 transmit and receive audio are (when all EQ
> settings are set to
> >> '0',
> >
> > Flat means the EQ does not add or subtract to the filter response
> > dialed
> > in by the operator with the SHIFT/WIDTH/HIGH CUT/LOW CUT
> controls.  The
> > high end and low end response will be dictated by those
> settings,  This
> > will be modified by the impedances in the path from the
> radio to the
> > headphones or speaker and the impedance of the headphones
> or speaker, or
> > the characteristics of the transformers and the overall
> impedances in
> > the LINE OUT case.
> >
> > Finally, the edges of the selected passband will be rolled
> off by the
> > action of the FIR filter windowing function applied to the filter
> > coefficients.
> >
> > 73,
> >
> > Lyle KK7P
> >

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