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K-3 RF Gain Calibration

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RLVZ

K-3 RF Gain Calibration

Mike,

Are you saying that your S-Meter reads 3-4 s-units MORE noise level now
that you did the RF Gain calibration with the XG-2? I was going to make the
same adjustment with my K-3. But if you are getting a 3-4 s-unit higher
noise level after the adjustment has been done... I won't be making the
adjustment as my K-3 is already more sensitive than I need on the low bands.
I'd use a 20dB ATT on the low bands often if I had one available. Perhaps
one day we'll be able to change the K-3's RF Gain per band via software to
help adapt to our local noise environment. (mine is very noisy on the low
bands with thunderstorm QRN off the Atlantic). For those who may be
concerned, yes I do use the RF Gain control.

73,
Dick- K9OM

Sorry if this comes across more than once, I'm having some e-mail issues.

I just did an RF gain calibration, using the XG2 and the K3 utility on
my kit K3 (built in Sept. '09).

There seems to be a dramatic difference in my noise level, 3-4 s units,
with a calibrated s-meter. I think I can pull more stuff out of the
ditches and weeds now.

Does that seem reasonable?

73, Mike NF4L

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Mike Reublin

Re: K-3 RF Gain Calibration

Hi Dick -

No, the noise level is less after the calibration. I'm one of those nuts
who considered the K3 to be noisy. I like it a LOT better now......and I
like it a lot before.

73,
Mike

[hidden email] wrote:

> Mike,
>
> Are you saying that your S-Meter reads 3-4 s-units MORE noise level now
> that you did the RF Gain calibration with the XG-2? I was going to make the
> same adjustment with my K-3. But if you are getting a 3-4 s-unit higher
> noise level after the adjustment has been done... I won't be making the
> adjustment as my K-3 is already more sensitive than I need on the low bands.
> I'd use a 20dB ATT on the low bands often if I had one available. Perhaps
> one day we'll be able to change the K-3's RF Gain per band via software to
> help adapt to our local noise environment. (mine is very noisy on the low
> bands with thunderstorm QRN off the Atlantic). For those who may be
> concerned, yes I do use the RF Gain control.
>
> 73,
> Dick- K9OM
>
>
> Sorry if this comes across more than once, I'm having some e-mail issues.
>
> I just did an RF gain calibration, using the XG2 and the K3 utility on
> my kit K3 (built in Sept. '09).
>
> There seems to be a dramatic difference in my noise level, 3-4 s units,
> with a calibrated s-meter. I think I can pull more stuff out of the
> ditches and weeds now.
>
> Does that seem reasonable?
>
> 73, Mike NF4L
>
>
>
>
> ______________________________________________________________
> 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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Home: http://mailman.qth.net/mailman/listinfo/elecraft
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N2TK

Re: K-3 RF Gain Calibration

In reply to this post by RLVZ

Maybe the S-meter needs to be calibrated as per the manual after the RF Gain
test?
With no antenna attached on 20M I get no reading on the S-meter. With the
antenna connected and no signals the S-meter kicks up to about S3. With a
50uV. signal the S-meter reads S9. That seems correct.

73,
N2TK, Tony

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of [hidden email]
Sent: Sunday, March 14, 2010 2:22 PM
To: [hidden email]
Subject: [Elecraft] K-3 RF Gain Calibration

Mike,

Are you saying that your S-Meter reads 3-4 s-units MORE noise level now
that you did the RF Gain calibration with the XG-2? I was going to make
the
same adjustment with my K-3. But if you are getting a 3-4 s-unit higher
noise level after the adjustment has been done... I won't be making the
adjustment as my K-3 is already more sensitive than I need on the low
bands.
I'd use a 20dB ATT on the low bands often if I had one available. Perhaps
one day we'll be able to change the K-3's RF Gain per band via software to
help adapt to our local noise environment. (mine is very noisy on the low
bands with thunderstorm QRN off the Atlantic). For those who may be
concerned, yes I do use the RF Gain control.

73,
Dick- K9OM

Sorry if this comes across more than once, I'm having some e-mail issues.

I just did an RF gain calibration, using the XG2 and the K3 utility on
my kit K3 (built in Sept. '09).

There seems to be a dramatic difference in my noise level, 3-4 s units,
with a calibrated s-meter. I think I can pull more stuff out of the
ditches and weeds now.

Does that seem reasonable?

73, Mike NF4L

______________________________________________________________
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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Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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n7ws

Re: K-3 RF Gain Calibration

In reply to this post by RLVZ

Maybe some clarification of what the "calibration" really does would be helpful.

The hardware AGC in the K3 operates on the post-filter FET IF amplifier and associated diodes. The "RF" gain control (really IF gain) under the control of the DSP adds a control voltage to the hardware AGC loop. If the manual gain control voltage exceeds the detected AGC voltage then it controls the IF gain, otherwise, it's in the hands of the AGC detector.

Unfortunately, there is variability (no pun intended) in the FET Gm, from device to device, hence for a given control voltage, each FET behaves differently. In comparison of my K3 to another, the differences were remarkable. In mine, even a slight reduction of manual gain caused an immediate and obvious degradation of SNR even on a BC station that was S9+50 dB. The comparison radio was much better behaved.

Anyone who has done any design work on receivers understands "delayed" AGC where the delay serves to keep the gain nearer the front end high enough to maintain SNR and only reduces it after the SNR is fully developed. Clearly, in my radio's case, the gain partitioning between the IF and DSP was being negatively affected and the SNR took a hit.

The RF gain calibration was a response to this issue and serves to measure the dB gain reduction vs. control voltage and develop a correction in firmware that linearizes (in dB) the curve.

Contrary to the belief of some, this isn't an S-meter calibration, although that is a secondary benefit. Likewise, absent the development of hardware AGC and/or the manual reduction of IF gain, it doesn't change the overall gain of the radio.

--- On Sun, 3/14/10, [hidden email] <[hidden email]> wrote:

> From: [hidden email] <[hidden email]>
> Subject: [Elecraft] K-3 RF Gain Calibration
> To: [hidden email]
> Date: Sunday, March 14, 2010, 12:22 PM
> Mike,
>
> Are you saying that your S-Meter reads 3-4 s-units MORE
> noise level now
> that you did the RF Gain calibration with the XG-2? I
> was going to make the
> same adjustment with my K-3. But if you are getting a
> 3-4 s-unit higher
> noise level after the adjustment has been done... I won't
> be making the
> adjustment as my K-3 is already more sensitive than I need
> on the low bands.
> I'd use a 20dB ATT on the low bands often if I had
> one available. Perhaps
> one day we'll be able to change the K-3's RF Gain per
> band via software to
> help adapt to our local noise environment.
> (mine is very noisy on the low
> bands with thunderstorm QRN off the Atlantic).
> For those who may be
> concerned, yes I do use the RF Gain control.
>
> 73,
> Dick- K9OM
>
>
> Sorry if this comes across more than once, I'm having some
> e-mail issues.
>
> I just did an RF gain calibration, using the XG2 and the
> K3 utility on
> my kit K3 (built in Sept. '09).
>
> There seems to be a dramatic difference in my noise
> level, 3-4 s units,
> with a calibrated s-meter. I think I can pull more
> stuff out of the
> ditches and weeds now.
>
> Does that seem reasonable?
>
> 73, Mike NF4L
>

Mike Reublin

Re: K-3 RF Gain Calibration

In reply to this post by N2TK

Good point, Tony. You missed the "calibrated s-meter" in my post though.

No antenna on 20M - S3
With antenna, no sigs - S10
50uV from the XG2 - S9

73, Mike

N2TK, Tony wrote:

> Maybe the S-meter needs to be calibrated as per the manual after the RF Gain
> test?
> With no antenna attached on 20M I get no reading on the S-meter. With the
> antenna connected and no signals the S-meter kicks up to about S3. With a
> 50uV. signal the S-meter reads S9. That seems correct.
>
> 73,
> N2TK, Tony
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of [hidden email]
> Sent: Sunday, March 14, 2010 2:22 PM
> To: [hidden email]
> Subject: [Elecraft] K-3 RF Gain Calibration
>
> Mike,
>
> Are you saying that your S-Meter reads 3-4 s-units MORE noise level now
> that you did the RF Gain calibration with the XG-2? I was going to make
> the
> same adjustment with my K-3. But if you are getting a 3-4 s-unit higher
> noise level after the adjustment has been done... I won't be making the
> adjustment as my K-3 is already more sensitive than I need on the low
> bands.
> I'd use a 20dB ATT on the low bands often if I had one available. Perhaps
> one day we'll be able to change the K-3's RF Gain per band via software to
> help adapt to our local noise environment. (mine is very noisy on the low
> bands with thunderstorm QRN off the Atlantic). For those who may be
> concerned, yes I do use the RF Gain control.
>
> 73,
> Dick- K9OM
>
>
> Sorry if this comes across more than once, I'm having some e-mail issues.
>
> I just did an RF gain calibration, using the XG2 and the K3 utility on
> my kit K3 (built in Sept. '09).
>
> There seems to be a dramatic difference in my noise level, 3-4 s units,
> with a calibrated s-meter. I think I can pull more stuff out of the
> ditches and weeds now.
>
> Does that seem reasonable?
>
> 73, Mike NF4L
>
>
>

Mike Reublin

Re: K-3 RF Gain Calibration

In reply to this post by n7ws

Definitely helpful Wes.

The S-meter cal is a whole separate process, right? Do I need to do that
again?

My ears, as well as the meter tell me I'm not hearing as much junk.
Meaning external noise, not internal.

73, Mike

Wes Stewart wrote:

> Maybe some clarification of what the "calibration" really does would be helpful.
>
> The hardware AGC in the K3 operates on the post-filter FET IF amplifier and associated diodes. The "RF" gain control (really IF gain) under the control of the DSP adds a control voltage to the hardware AGC loop. If the manual gain control voltage exceeds the detected AGC voltage then it controls the IF gain, otherwise, it's in the hands of the AGC detector.
>
> Unfortunately, there is variability (no pun intended) in the FET Gm, from device to device, hence for a given control voltage, each FET behaves differently. In comparison of my K3 to another, the differences were remarkable. In mine, even a slight reduction of manual gain caused an immediate and obvious degradation of SNR even on a BC station that was S9+50 dB. The comparison radio was much better behaved.
>
> Anyone who has done any design work on receivers understands "delayed" AGC where the delay serves to keep the gain nearer the front end high enough to maintain SNR and only reduces it after the SNR is fully developed. Clearly, in my radio's case, the gain partitioning between the IF and DSP was being negatively affected and the SNR took a hit.
>
> The RF gain calibration was a response to this issue and serves to measure the dB gain reduction vs. control voltage and develop a correction in firmware that linearizes (in dB) the curve.
>
> Contrary to the belief of some, this isn't an S-meter calibration, although that is a secondary benefit. Likewise, absent the development of hardware AGC and/or the manual reduction of IF gain, it doesn't change the overall gain of the radio.
>
>
>
> --- On Sun, 3/14/10, [hidden email] <[hidden email]> wrote:
>
>
>> From: [hidden email] <[hidden email]>
>> Subject: [Elecraft] K-3 RF Gain Calibration
>> To: [hidden email]
>> Date: Sunday, March 14, 2010, 12:22 PM
>> Mike,
>>
>> Are you saying that your S-Meter reads 3-4 s-units MORE
>> noise level now
>> that you did the RF Gain calibration with the XG-2? I
>> was going to make the
>> same adjustment with my K-3. But if you are getting a
>> 3-4 s-unit higher
>> noise level after the adjustment has been done... I won't
>> be making the
>> adjustment as my K-3 is already more sensitive than I need
>> on the low bands.
>> I'd use a 20dB ATT on the low bands often if I had
>> one available. Perhaps
>> one day we'll be able to change the K-3's RF Gain per
>> band via software to
>> help adapt to our local noise environment.
>> (mine is very noisy on the low
>> bands with thunderstorm QRN off the Atlantic).
>> For those who may be
>> concerned, yes I do use the RF Gain control.
>>
>> 73,
>> Dick- K9OM
>>
>>
>> Sorry if this comes across more than once, I'm having some
>> e-mail issues.
>>
>> I just did an RF gain calibration, using the XG2 and the
>> K3 utility on
>> my kit K3 (built in Sept. '09).
>>
>> There seems to be a dramatic difference in my noise
>> level, 3-4 s units,
>> with a calibrated s-meter. I think I can pull more
>> stuff out of the
>> ditches and weeds now.
>>
>> Does that seem reasonable?
>>
>> 73, Mike NF4L
>>
>>