K3 RF Gain control reduced range after RF gain calibration

[Nate Bargmann]

This is strange.

In an effort to better align the P3's idea of signal strength with that
of the K3's, I performed the K3 RF Gain Calibration, then the S-meter
calibration and finally the P3 level calibration.  I did the
calibrations at 7040 kHz using a service monitor as the signal source
for 50 uV and 1 uV sources following the procedures in the manuals.

This evening after tuning to 75m for the section nets, I set the RF Gain
control to its usual 2 O'clock setting and realized the background noise
was still quite pronounced.  I found that I have to turn the RF Gain
control to between 9 and 10 O'clock to reduce the noise as before at 2
O'clock.  Also, the S-meter level no longer reflects the change as the
RF Gain is reduced.  Before putting the RF Gain control fully CCW
resulted in the S-meter reading full scale (changine the S-meter mode to
NOR or ABS and resetting the calibration values had any effect).
Switching to a dummy load reveals that as the RF control is reduced that
the S-meter bars light to about S4 and no higher regardless of how far
CCW the knob is turned.  I've also noticed that with the control fully
CCW that the receiver is not completely muted (I think it was before,
but not sure).

I did goof on the first run through the RF Gain calibration by having
the control reduced slightly--around 4 O'clock--and not fully CW as
stated in the manual.  Yup, my error from being in a hurry.  I realized
the mistake and ran the routine again with the RF Gain control fully CW.

I used the Linux K3 utility 1.4.1.8 and had the P3 inline and on while I
performed the calibration.  Was having the P3 on at the same time a
mistake?  I also reloaded all of the firmware--MCU 4.39, FPF 1.14 and
DSP1 2.73 with no change in behavior.

Thanks!

73, de Nate N0NB >>

--

"The optimist proclaims that we live in the best of all
possible worlds.  The pessimist fears this is true."

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[Nate Bargmann]

Well, I think I "solved" the issue.  I reset the RF Gain back to factory
defaults with the K3 utility and then set the S-meter to NOR and SMTR OF
and SC to the factory defaults.  It appears the RF Gain is back to
normal.  Perhaps it's best to leave this stuff well enough alone!

73, de Nate N0NB >>

--

"The optimist proclaims that we live in the best of all
possible worlds.  The pessimist fears this is true."

Ham radio, Linux, bikes, and more: http://www.n0nb.us
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[hb9brj]

Nate,

Take a look at a similar problem (and its solution) I had some time ago:
http://elecraft.365791.n2.nabble.com/K3-Rf-gain-tracking-main-vs-sub-tp5668917p5676134.html

73, Markus HB9BRJ

[Nate Bargmann]

* On 2011 20 Dec 23:22 -0600, hb9brj wrote:
> Nate,
>
> Take a look at a similar problem (and its solution) I had some time ago:
> http://elecraft.365791.n2.nabble.com/K3-Rf-gain-tracking-main-vs-sub-tp5668917p5676134.html

Thanks, Markus.

I do recall that thread now.  I was just after I got my K3 on the air
and was too busy learning other things to pay attention.  After reading
the thread I didn't see a definite solution and that it was being
investigated.

I think I'll try with the service monitor again this evening and see
what happens.

73, de Nate N0NB >>

--

"The optimist proclaims that we live in the best of all
possible worlds.  The pessimist fears this is true."

Ham radio, Linux, bikes, and more: http://www.n0nb.us
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[Cady, Fred]

There does seem to be something strange in the way the RF gain works.
I also see the 10 dB change in audio level at the 9 o'clock position.
In addition, the RF gain position seems to affect the way the AGC on and
off works as shown on http://www.ke7x.com/home/miscellaneous-k3-information/unexpected-agc-behavior

Happy holidays all.
73,
Fred, KE7X
"The Elecraft K3: Design, Configuration, and Operation"



-----Original Message-----
From: [hidden email] on behalf of hb9brj
Sent: Tue 12/20/2011 10:21 PM
To: [hidden email]
Subject: Re: [Elecraft] K3 RF Gain control reduced range after RF gaincalibration
 
Nate,

Take a look at a similar problem (and its solution) I had some time ago:
http://elecraft.365791.n2.nabble.com/K3-Rf-gain-tracking-main-vs-sub-tp5668917p5676134.html

73, Markus HB9BRJ

--
View this message in context: http://elecraft.365791.n2.nabble.com/K3-RF-Gain-control-reduced-range-after-RF-gain-calibration-tp7113809p7114181.html
Sent from the Elecraft mailing list archive at Nabble.com.
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[alorona]

Fred, are you expecting the AGC OFF curves to always produce higher output than
the ON curves? I'm not sure that's a correct assumption. I think the purpose of
OFF is that you have control over the curve, that is, where you place the linear
part of the dynamic range. It's like a variable attenuator in a spectrum
analyzer.

There are two truths regarding AGC OFF:

As you reduce the RF Gain you should see a drop in audio output.

AGC ON is always going to give you a more compressed input-output
characteristic, compared to AGC OFF. That's what AGC does; it wants to make
signals equal to a greater or lesser extent depending on your AGC parameters.

It looks like your measurements have proven these two truths.

A sudden 10 dB jump at the 9 o'clock or any position is an issue. This brings
up a good point... all those who have been experiencing 'pileup mush' should
make sure that their RF calibration is correct. I bet you that's half of the
problem.

Al  W6LX




________________________________
There does seem to be something strange in the way the RF gain works.
I also see the 10 dB change in audio level at the 9 o'clock position.
In addition, the RF gain position seems to affect the way the AGC on and
off works as shown on
http://www.ke7x.com/home/miscellaneous-k3-information/unexpected-agc-behavior 
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[Cady, Fred]

Thanks Al.
Well, the Figure 1 shows what I expected. Below the AGC gain threshold the output audio is the same with AGC on and off. Figure 2 is not expected, at least for me. Reducing the RF gain ought to reduce the audio levels, which you point out, and which it does. But, it reduces the AGC off signals more than the AGC on as shown in Figure 2. I made these measurements in the context of wondering why I find it necessary and and an improvement to turn AGC off when there is a pileup of signals all of about the same signal strength, something that has happened frequently for me when operating from C6. During our last operation, it was a real pain to switch AGC off and then have to turn up audio gain to compensate. It just seems strange to me that when AGC is on and we are below the AGC threshold, that the RF-audio level audio transfer characteristic is different than when AGC is off.
73 and happy holidays all,
Fred
KE7X




-----Original Message-----
From: [hidden email] on behalf of Al Lorona
Sent: Wed 12/21/2011 10:46 AM
To: [hidden email]
Subject: Re: [Elecraft] K3 RF Gain control reduced range after RFgaincalibration
 
Fred, are you expecting the AGC OFF curves to always produce higher output than
the ON curves? I'm not sure that's a correct assumption. I think the purpose of
OFF is that you have control over the curve, that is, where you place the linear
part of the dynamic range. It's like a variable attenuator in a spectrum
analyzer.

There are two truths regarding AGC OFF:

As you reduce the RF Gain you should see a drop in audio output.

AGC ON is always going to give you a more compressed input-output
characteristic, compared to AGC OFF. That's what AGC does; it wants to make
signals equal to a greater or lesser extent depending on your AGC parameters.

It looks like your measurements have proven these two truths.

A sudden 10 dB jump at the 9 o'clock or any position is an issue. This brings
up a good point... all those who have been experiencing 'pileup mush' should
make sure that their RF calibration is correct. I bet you that's half of the
problem.

Al  W6LX




________________________________
There does seem to be something strange in the way the RF gain works.
I also see the 10 dB change in audio level at the 9 o'clock position.
In addition, the RF gain position seems to affect the way the AGC on and
off works as shown on
http://www.ke7x.com/home/miscellaneous-k3-information/unexpected-agc-behavior 
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[Dave Hachadorian]

> I find it necessary and and an improvement to turn AGC off when
> there is a pileup of signals all of about the same signal
> strength, something that has happened frequently for me when
> operating from C6.

Try this trick:
http://elecraft.365791.n2.nabble.com/K3-in-a-CW-pileup-td7110599.html#a7110710


Dave Hachadorian, K6LL
Yuma, AZ













































.

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[Cady, Fred]

Thanks Dave. I saw that trick earlier and its pretty neat. I guess one could make a macro to turn AGC off, reduce RF gain and increase AF gain to keep the signal audio levels the same, like Figure 1.


-----Original Message-----
From: David Hachadorian on behalf of Dave Hachadorian
Sent: Wed 12/21/2011 1:22 PM
To: Cady, Fred; Elecraft Reflector
Subject: Re: [Elecraft] K3 RF Gain control reduced range afterRFgaincalibration
 
> I find it necessary and and an improvement to turn AGC off when
> there is a pileup of signals all of about the same signal
> strength, something that has happened frequently for me when
> operating from C6.

Try this trick:
http://elecraft.365791.n2.nabble.com/K3-in-a-CW-pileup-td7110599.html#a7110710


Dave Hachadorian, K6LL
Yuma, AZ













































.


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[ab2tc]

Hi,

I think your symptoms with the erratic RF gain control is typical of the receiver RF gain calibration going awry. This procedure is very fragile and tends to end you up with symptoms like this. Do you have the latest version of the K3 utility? There was a problem with an earlier version that would not do the receiver gain calibration correctly. I would repeat the calibration. Make sure you follow the instructions exactly and be very careful to position the test signal exactly in the center of the very narrow passband specified. Once this calibration succeeds, the RF gain control should have the S-meter rise smoothly to S9+60 as you back off the RF gain. Mine does, but it took me three tries of the calibration procedure.

AB2TC - Knut

Cady, Fred wrote

Thanks Dave. I saw that trick earlier and its pretty neat. I guess one could make a macro to turn AGC off, reduce RF gain and increase AF gain to keep the signal audio levels the same, like Figure 1.


<snip>

[Nate Bargmann]

I received a message from K1GQ that he was having similar trouble as me
with the RF gain calibration.  This evening I tackled it again but this
time I was certain that the P3 was OFF each time.  I also did it on 20m
in addition to 40m and each time the calibration worked as expected.
The moral to my tale is to only have the K3 on when calibrating it.

73, de Nate N0NB >>

--

"The optimist proclaims that we live in the best of all
possible worlds.  The pessimist fears this is true."

Ham radio, Linux, bikes, and more: http://www.n0nb.us
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