K3 AGC Settings Tutorial

[KK7P]

BACKGROUND

There has been a lot of confusion about AGC in the K3.  Some of it is
AGC related, some of it is AGC interaction with noise reduction (NR).

A later email will address the noise reduction issue. For now, let';s
look at the AGC apart from NR.

---

WHY DID THE AGC CHANGE?

WHen we interoduced the HAGC mod a few months ago, it increased the
dynamic range of the radio before "Hardware AGC" (HAGC) kicked in. HAGC
is there to protect the analog to digital converter (ADC) from
over-range.  The mod required that the DSP AGC cover a wider range.

It turned out that the DSP AGC was not doing the job it was intended to
do on these stronger signals.  We were receiving a steady stream of
complaints about loud signals being almost painful to K3 operators using
headphones.  IF flat (SLOE=15) was selected it worked fine, but other
settings resulted in excessive signal strength.

The AGC control algorithm was recently changed to compensate for this
problem.  At the same time, the AGC threshold range was adjusted to more
closely mimic earlier K3 AGC threshold behavior.

---

HOW SHOULD I ADJUST THE AGC?

For most of us, the K3 AGC is simply a matter of OFF|FAST|SLOW.
HOwever, many peopl prefer an AGC that starts on band noise; others want
it to start with a weak to moderate signal.

Some people like the audio level to be constant once AGC has been
activated' others want some sense of increasing loudness as the signal
strength increases.

Here is how I suggest you set the AGC for your needs.

1) CONFIG:TECH MD ON

This exposes the AGC parameters you can adjust.

2) CONFIG:AGC SLP 015

This makes the audio response flat once the AGC threshold has been reached.

3) CONFIG:AGC THR

Tune around and and adjust this to the desired threshold.  A low number
means a weaker signal (or noise) will activate the AGC.

Note: THE AGC does NOT drive the S METER, so don't make the mistake of
conditioning yourself to look at S METER action and think you are seeing
the affects of AGC adjustments.

Note: Different bands and different days have different amounts of
noise.  A noise QRN-filled summer noise level is very different than a
quiet winter evening's noise level.  The AGC doesn't know the
difference, so it is up to you to change things if you desire different
thresholds on a seasonal basis.

4) CONFIG:AGC SLP

Now that you have the threshold chosen, tune across loud and weak
signals.  Adjust the SLP parameter so that stronger signals sound louder
  by reducing this value from 15.  If you want everything to be "flat"
above the threshold, leave it at 15.

---

WHAT IS NEXT?

The changes to the AGC have not pleased everyone.  We are embarking on a
modification and test program to further improve it.  Watch this space!

---

AGC - OTHER

You can also adjust the decay rates for FAST (CONFIG:AGC F) and SLOW
(CONFIG:AGC S).  Larger values indicate faster decay.  The amount of
HOLD time that AGC SLOW uses before it commences decay is also settable
(CONGIF:AGC HLD).

Most people seem to be happy with the defaults.

Thank you for your patience and we continue to work to make the K3 YOUR
radio.

73,

Lyle KK7P


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[AD6XY]

Thanks for the explanation. As you say, noise levels differ between bands and over time E.g. 80m in Summer compared to Winter or HF versus 50MHz and higher bands via a transverter. Does the AGC setting apply per band or does it cover all bands?

AGC also depends on mode, CW vs SSB bandwidths. Again, does it differ?

If so there will be an awful lot of tweeking needed for all possible combinations.

73 Mike

Lyle Johnson wrote

Note: Different bands and different days have different amounts of
noise.  A noise QRN-filled summer noise level is very different than a
quiet winter evening's noise level.  The AGC doesn't know the
difference, so it is up to you to change things if you desire different
thresholds on a seasonal basis.

[KK7P]

> Thanks for the explanation. As you say, noise levels differ between bands and
> over time E.g. 80m in Summer compared to Winter or HF versus 50MHz and
> higher bands via a transverter. Does the AGC setting apply per band or does
> it cover all bands?

AGC is AGC. It is not per band, it is per radio :-)

> AGC also depends on mode, CW vs SSB bandwidths. Again, does it differ?

Use AGC OFF | FAST | SLOW

Most people prefer FAST for CW and SLOW for SSB.

> If so there will be an awful lot of tweeking needed for all possible
> combinations.

I do not know of a radio with per band AGC settings, or per season.
Most radios don't let you adjust the threshold or slope -- or the decay
rate of FAST and SLOW.

With the K3 we allow you to tailor the AGC; we don't require that you
tailor it.

73,

Lyle KK7P

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[Jim Garland]

*****************************
AGC is AGC. It is not per band, it is per radio :-)

I do not know of a radio with per band AGC settings, or per season.
Most radios don't let you adjust the threshold or slope -- or the decay
rate of FAST and SLOW.
With the K3 we allow you to tailor the AGC; we don't require that you
tailor it.

73,

Lyle KK7P
*****************************

It is true that the AGC pertains to the radio and not the band, but the optimal AGC threshold setting does vary by band.  On 80m, for example, I set the AGC threshold on my Ten-Tec Orion at about 20uV.  On 10m, where the noise level is very low, I set it at 0.5uV. The Orion, incidentally, has fast, medium, and slow AGC settings, plus a custom "prog" setting, and one can set the threshold, decay rate and hang time independently for each speed. It is possible to spend hours fiddling with the Orion's AGC settings.

73,

Jim W8ZR



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[W8JI]

It is true that the AGC pertains to the radio and not the
band, but the optimal AGC threshold setting does vary by
band.  On 80m, for example, I set the AGC threshold on my
Ten-Tec Orion at about 20uV.  On 10m, where the noise level
is very low, I set it at 0.5uV. The Orion, incidentally, has
fast, medium, and slow AGC settings, plus a custom "prog"
setting, and one can set the threshold, decay rate and hang
time independently for each speed. It is possible to spend
hours fiddling with the Orion's AGC settings.>>

One of the reasons you have to change it so much is any AGC
that has no effect at all until a threshold and then tips in
all at once is always critical to adjust. A good AGC system
has a slope rather than a hard threshold with no AGC at all
below a point, and then hard AGC after that point that
clamps the volume to one level.

At quiet locations the dominant noise is propagated via
skywave just like the desired signals. This means the noise
floor varies greatly with direction depending on propagation
or even the time of day. On the same band in different
directions the noise floor can vary 10 or 20 dB. This
requires constant adjustment of AGC threshold with any AGC
that tips in fully at a threshold.

AGC systems with a slope don't exaggerate the problem of
noise level changes and they don't "muddy" the signals into
one constant level or no AGC at all.

When I solid stated my R4C's I built a new AGC circuit. I
put a lot of gain in the AGC, there was very little audio
level change with input signal level change. On the bench it
was nearly perfect, once the AGC started working everything
stayed at nearly the same audio level. I worked to make it
have flat audio level with varying signal levels, textbook
perfect AGC.

Everyone hated it. It required constant riding of RF gain.
It made weak DX stations near noise floor muddy up or
vanish, and it was impossible to sort signals close in pitch
in pileups.

Decreasing the gain in the AGC circuit cured it, and it was
no longer necessary to ride the RF gain (same as adjusting
AGC threshold).

The K3 has an AGC SLP adjustment that cures this problem. I
was delighted to see the people at Elecraft included an AGC
slope adjustment, and that it works to make the AGC have
that "analog" sound operators here like for handling pileups
and for weak signals in rough noise. Unless you have an old
analog AGC system the slope adjustment is a "must have"
requirement. Especially for people who work pileups or work
DX that is in and out of rough noise like static crashes.

Although I just started using the K3, I really like the AGC
system so far. That's in contrast to other digital AGC
systems I quickly learned to *dislike*. Low band DXers or
contesting people will really like the "slope adjustment"
feature.

73 Tom




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