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David Gilbert

Re: K3 AGC Mush

When I experience the problem the signals are all quite close ...
probably within a 30 Hz window, but not exactly the same. My hearing
isn't as good as it was when I was younger (mostly high frequency loss
above 10 KHz), but I can tell when signals are exactly the same and if
that was the issue I'd obviously never be complaining about that. The
RIT on the K3 varies in 10 Hz steps and that difference is very
noticeable to me, so it would not normally be difficult for me to
separate a few pileup signals within that 30 Hz window if frequency was
the only factor.

As you mentioned, signals are often very close these days. People are
using narrower and narrower receive filters and that puts them more
precisely on frequency than in the past, and of course packet cluster
spots put callers pretty close on frequency subject only to the accuracy
of their rigs.

As I mentioned in another post, I think these are the key conditions for
the problem:

a. the signals need to be close enough that the children
(sum/difference mixer products) overlap in frequency with the parents

b. the signals need to be keyed, which makes me suspect at least some
gain non-linearity that varies with time. The addition of AFC-SOFT
represented an significant improvement, but not enough. Possibly some
insight into this aspect of the problem might be gained by varying the
keying speeds and observing the effect. Even there is not a time
non-linearity, though, having keyed signals is important. In real life,
keyed signals help us mentally separate signals spaced closer in
frequency than if they were not keyed.

c. The signals need to be weak, which makes me convinced that there is
a gain non-linearity at the low end. I can't really quantify just how
weak, but I would estimate less than S-2 and it seems to get worse as
the signals get weaker. I have a very low ambient noise level here and
S-1 signals are typically quite readable. Strong signals do not cause
the problem we are discussing here.

Hope some of this helps.

73,
Dave AB7E

On 12/4/2011 1:31 PM, Eric Swartz WA6HHQ - Elecraft wrote:

> We actually have a 'pile-up' generator we designed that sends multiple
> cw signals. So far it has not reproduced the issue here.
>
> What is the signal spacing you are hearing this with? All -exactly- on
> the same freq? Or spread out?
>
> 73, Eric
>
> _..._
>

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wayne burdick

Re: K3 hardware AGC experiment shows promise

Administrator

In reply to this post by Joe Subich, W4TV-4

Joe Subich, W4TV wrote:

> Remember, IMD is driven by total *peak* signal level. The peak signal
> level is not simply the scalar sum of the levels ... it is a vector
> sum as the individual signals add in phase.

And those peaks could be slightly modulating the AGC loop.

Wayne

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w0mu

Re: K3 hardware AGC experiment shows promise

In reply to this post by wayne burdick

This is why I bought an Elecraft. Good luck getting this type of
support with IKY. I would try the mod but since I haven't noticed the
issue, I don't think it makes sense for me to try.

We were not digging signals out of the mud in J6 except for 160 but
nobody mentioned any issues.

On 12/4/11 6:50 PM, Wayne Burdick wrote:

> Hi all,
>
> The K3's hardware AGC time constant is a compromise between recovery
> time and IMD due to modulation of the loop. C238, on the bottom of the
> RF board near the front, sets this time constant.
>
> We did a little experiment today (thanks to Tree, N6TR) that suggests
> increasing the size of C238 substantially might be a worthy change. In
> the case of signals just large enough to tickle the hardware AGC, the
> first IMD products were reduced by something like 18 dB. This will
> also increase the recovery time for very strong signals, so the jury
> is out on whether this is OK for the average user.
>
> For the experimentally inclined: C238 is easy to get to; just remove
> bottom cover A (the front half). C238 is a large-ish surface mount
> capacitor nestled between two 20-pin connectors. The present value is
> 0.1 uF. Tree tacked a 1-uF cap on top of it. Then he tacked another
> one on, which improved things by another few dB.
>
> Some ops have mentioned problems with signals much lower than this,
> which has always baffled me. But I got to thinking: Suppose you're
> listening to a bunch of S4-S5 signals in your DSP passband. You could
> have larger signals outside the DSP, but inside the crystal filter. Or
> you could have clicks from strong signals that get inside the crystal
> filter but you can't hear because you're using a narrow DSP filter. Or
> you could have noise spikes. Any of these could ping the hardware AGC
> just enough to cause IMD between all of the signals in the passband.
>
> My point is that increasing the loop time constant could have a more
> general benefit when a band is busy and/or noisy.
>
> Let me know if you try this and whether the results are of interest.
> (I live in an RF-free zone, it seems, so I can never recreate the
> problem here. Frustrating!)
>
> 73,
> Wayne
> N6KR
>
>
>
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Guy, K2AV

Re: K3 hardware AGC experiment shows promise

In reply to this post by wayne burdick

I should point out that the very common habit of not using the ATT or
even turning on the PRE on lower bands would be commonly putting this
circuit in this condition. Perhaps that is why there is a contingent
of us that never seems to have the problems reported. Constantly
running the RF end at max gain is bad for other reasons besides.

Since the DSP AGC treats the outcome of the hardware AGC and the RF
string switch settings as "propagation", why would the hang time
matter?

If it was me, I would be working on something in firmware that did NOT
leave it to the user to remember to turn off PRE and turn on ATT based
on the signal levels being slammed into the hardware AGC.

73, Guy.

On Sun, Dec 4, 2011 at 8:50 PM, Wayne Burdick <[hidden email]> wrote:

David Gilbert

Re: K3 hardware AGC experiment shows promise

In reply to this post by Joe Subich, W4TV-4

I find those comments exceptionally interesting, Joe.

a. it might help explain why keyed CW signals seem (in my experience,
at least) to be a bigger issue .. more yanking around of the AGC.

b. it might help explain why at least some of us feel that the issue is
worse for weaker signals. The AGC is definitely less linear at the low
end (I use K8ZOA's web site for reference), but if signals were
uniformly weak that wouldn't be such an issue since weak signals
wouldn't have much level excursion anyway. But if the P - P effect you
describe is repeatedly dragging the AGC across that really non-linear
portion of the curve I would think it could cause a lot of mixing.

73,
Dave AB7E

On 12/4/2011 7:36 PM, Joe Subich, W4TV wrote:

> > Some ops have mentioned problems with signals much lower than this,
> > which has always baffled me.
>
> Remember, IMD is driven by total *peak* signal level. The peak signal
> level is not simply the scalar sum of the levels ... it is a vector
> sum as the individual signals add in phase. W8FN explained some of the
> constraints in terms of peak to average power of multiple CDMA transmit
> signals and IMD ... the same applies to receive signals and the peak
> voltage handling capability in the IF amplifier/ADC. Six to 10 S4-S5
> signals can create a greater peak voltage (if just for the shortest
> time) than a single S9+40 signal.
>
> It's been 25 years since I was exposed to the math behind this (as part
> of work in dealing with multiplexed power amplifiers for analog TV) but
> it would be instructive to convert the average power levels of a bunch
> of S4-S5 signals to P-P voltage, sum those P-P values and convert the
> peak voltage back to power levels to see the true impact. Solid state
> IF amplifiers and particularly DACs don't have the soft compression
> characteristics we were used to with remote cut-off pentodes or even
> dual gate MOSFETs in the analog receivers of previous generations.
>
> 73,
>
> ... Joe, W4TV
>
>
> On 12/4/2011 8:50 PM, Wayne Burdick wrote:
>> Hi all,
>>
>> The K3's hardware AGC time constant is a compromise between recovery
>> time and IMD due to modulation of the loop. C238, on the bottom of the
>> RF board near the front, sets this time constant.
>>
>> We did a little experiment today (thanks to Tree, N6TR) that suggests
>> increasing the size of C238 substantially might be a worthy change. In
>> the case of signals just large enough to tickle the hardware AGC, the
>> first IMD products were reduced by something like 18 dB. This will
>> also increase the recovery time for very strong signals, so the jury
>> is out on whether this is OK for the average user.
>>
>> For the experimentally inclined: C238 is easy to get to; just remove
>> bottom cover A (the front half). C238 is a large-ish surface mount
>> capacitor nestled between two 20-pin connectors. The present value is
>> 0.1 uF. Tree tacked a 1-uF cap on top of it. Then he tacked another
>> one on, which improved things by another few dB.
>>
>> Some ops have mentioned problems with signals much lower than this,
>> which has always baffled me. But I got to thinking: Suppose you're
>> listening to a bunch of S4-S5 signals in your DSP passband. You could
>> have larger signals outside the DSP, but inside the crystal filter. Or
>> you could have clicks from strong signals that get inside the crystal
>> filter but you can't hear because you're using a narrow DSP filter. Or
>> you could have noise spikes. Any of these could ping the hardware AGC
>> just enough to cause IMD between all of the signals in the passband.
>>
>> My point is that increasing the loop time constant could have a more
>> general benefit when a band is busy and/or noisy.
>>
>> Let me know if you try this and whether the results are of interest.
>> (I live in an RF-free zone, it seems, so I can never recreate the
>> problem here. Frustrating!)
>>
>> 73,
>> Wayne
>> N6KR
>>
>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
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>>
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>>
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gm3sek

Re: K3 hardware AGC experiment shows promise

In reply to this post by wayne burdick

Wayne Burdick wrote:
>Joe Subich, W4TV wrote:
>
>> Remember, IMD is driven by total *peak* signal level. The peak signal
>> level is not simply the scalar sum of the levels ... it is a vector
>> sum as the individual signals add in phase.
>
>And those peaks could be slightly modulating the AGC loop.
>

Maybe that should say "modulating the AGC loops" (plural)? The HAGC loop
and the DSP AGC loop interact strongly - especially around the HAGC
threshold - and this creates the possibility for each loop to modulate
the other.

When the HAGC begins to act, we know that the firmware automatically
adjusts the DSP AGC to give consistent audio levels and correct S-meter
readings. The firmware monitors for HAGC action by digitizing the
voltage on the HAGC1 line, but there has to be some delay before it can
become "aware" of any change. The dynamics of this process create the
possibility for the HAGC loop and the DSP AGC loop to modulate each
other.

As far as I'm aware, this feature is unique to the K3, which may help to
explain the "rig-specific" nature of the problem. If this is a valid
model, the effects would predictably be worst around the HAGC threshold
where the response is inherently nonlinear. The dynamic interaction
between the two loops would be quite sensitive to the rate(s) of
amplitude variation in the composite incoming signal, as individual
components are keyed on and off. It would also be affected by added
noise, due to its dependency on the instantaneous vector sum of *all*
incoming signal, noise and interference components hitting the HAGC
detector (as identified by W4TV).

The mathematics of two cascaded feedback loops are way beyond me, but
the benefit of increasing the HAGC time constant by a very large factor
(10-20) sounds at lot like avoiding competition between the dominant
poles in the two loops. But the same model also explains why this
wouldn't be a complete cure.

This is all speculation, because much depends on hidden detail in the
DSP AGC firmware... but might it make some sense?

--

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek
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Geoffrey Mackenzie-Kennedy-3

Re: K3 hardware AGC experiment shows promise

In reply to this post by Joe Subich, W4TV-4

Joe,

You may recall that the subject of K3 "Mush" was discussed on the K3
Contesters Forum earlier this year, and that I suggested that the Group
Delay Variations introduced by the narrower bandwidth roofing filters might
well be the cause of the "Mush" problem. The recordings of K3's audio sent
to me by two owners of the K3 supported this thought, as did the plots made
by another K3 owner of the Delay vs. frequency introduced by roofers of
differing bandwidths.

A second thought, which I could not post before leaving Scotland, was that
the termination of the roofing filter would seem to vary when the HAGC
becomes activeThis raises two further points:

1) "What effect does an active HAGC have on a roofer's Group Delay
Variations?"

2) "What effect does an active HAGC have on a roofer's Output Odd Order
Intercepts (in and outside of the filter's passband), and does this increase
the level of filter generated IMD products enough to create audible "mush"?

Unfortunately adding a simple resistive pad to isolate the roofer's output
from the HAGC's IF circuitry could increase the overall Noise Figure of the
receiver too much.

It is my understanding that not all K3s exhibit this "mush problem". This
does not surprise me because the Delay characteristics of the roofers are
probably not specified to keep their cost within affordable limits - i.e.
some K3 roofers of x bandwith might exhibit fairly constant delay vs.
frequency, others might be quite "wild".

73,

Geoff
LX2AO

On Monday, December 05, 2011 3:36 AM, Joe Subich W4TV wrote:

> Remember, IMD is driven by total *peak* signal level. The peak signal
> level is not simply the scalar sum of the levels ... it is a vector
> sum as the individual signals add in phase. W8FN explained some of the
> constraints in terms of peak to average power of multiple CDMA transmit
> signals and IMD ... the same applies to receive signals and the peak
> voltage handling capability in the IF amplifier/ADC. Six to 10 S4-S5
> signals can create a greater peak voltage (if just for the shortest
> time) than a single S9+40 signal.

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Barry N1EU

Re: K3 hardware AGC experiment shows promise

In reply to this post by wayne burdick

wayne burdick wrote

Hi all,

The K3's hardware AGC time constant is a compromise between recovery
time and IMD due to modulation of the loop. C238, on the bottom of the
RF board near the front, sets this time constant.

We did a little experiment today . . .

I think it would be informative to monitor whether the HAGC is indeed kicking in during the variety of pileup mush type events not involving very strong signals in the passband.

For example, could a very visible LED be set up external to the rig that would flash when HAGC kicks in? A few of us could operate like this in an upcoming contest (e.g., next weekend 10M contest) and confirm whether there's correlation between HAGC and pileup mush.

Barry N1EU

Cady, Fred

Re: K3 hardware AGC experiment shows promise (& KE7X config)

In reply to this post by wayne burdick

Hi Wayne,
I'd be happy to try the modification. I can do it with one K3 and not
with the other.

For reference, here are my configurations and general operation settings
when in C6.
AF GAIN = high. (I'm thinking maybe to set it low)
AF LIM 20
AGC DCY SOFT
AGC HLD 0.30
AGC PLS NOR
AGC SLP 0
AGC THR 8
AGC-F 120
AGC-S 020
SER NUM 1148
RX EQ 1 -16
RX EQ 2 -16
RX EQ 3 0
RX EQ 4 +6
RX EQ 5 +6
RX EQ 6 0
RX EQ 7 -10
RX EQ 8 -16

When operating, ATT is ALWAYS ON. I don't think I ever took it off
except maybe when 15 was dead. PRE never on.

RF gain - all over the lot - say between 9 and 3. When there were lots
of big signals I'd crank it back and then forget to turn it up again and
would CQ in the face of weak callers :-(

AF Gain - all over the lot too.

I have 250, 400, 1000 and 2.7 kHz filters.

DSP _usually_ in the 500 - 700 range, sometimes a little wider,
sometimes a little narrower. I don't think I ever went below 300 Hz.

AFX never on. I don't' like it but it might be interesting to try.
I use Bose QC2 headphones.
I wear hearing aids.

Most mods have been done to the K3s including the stiffeners on the
synthesizers and I have swapped out the DSP boards. I have not done the
HAGC mod.

73,
Fred KE7X

Fred Cady
fcady at ieee dot org

> -----Original Message-----
> From: [hidden email] [mailto:elecraft-
> [hidden email]] On Behalf Of Wayne Burdick
> Sent: Sunday, December 04, 2011 6:59 PM
> To: Elecraft Reflector
> Subject: Re: [Elecraft] K3 hardware AGC experiment shows promise
>
> By the way, we'll be happy to send out these surface-mount 1 uF
> capacitors (or whatever we determine is the best value) to anyone who
> would like to try the experimental mod, immediately and at no charge.
>
> These are huge as SMD parts go. Anyone with a fine-tip iron would have
> no trouble putting one in. There's no need to take the original,
> smaller one off; you can just stack the new one on top.
>
> If you're in a hurry, you could use any type of capacitor that will
> fit, including an electrolytic. Just be sure to put the (-) end at
> ground if you use a polarized capacitor.
>
> 73,
> Wayne
> N6KR
>
>
> On Dec 4, 2011, at 5:50 PM, Wayne Burdick wrote:
>
>
> > The K3's hardware AGC time constant is a compromise between recovery
> > time and IMD due to modulation of the loop. C238, on the bottom of
> the
> > RF board near the front, sets this time constant.
> >
> > We did a little experiment today
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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w0mu

Re: K3 hardware AGC experiment shows promise (& KE7X config)

Just for comparison and I don't have the K3 that we used unpacked yet so
I don't know the agc settings.

I use AFX all the time. ATT was almost never engaged. I never use RX
equalization. RF gain was used mostly on the low bands.

When I had Bose headphones I noticed that they were quite prone to
pickup RF.

Filters: 200 400 1000 1.8 2.8 Sub 400 and 2.8

On 12/5/11 6:09 AM, Cady, Fred wrote:

> Hi Wayne,
> I'd be happy to try the modification. I can do it with one K3 and not
> with the other.
>
> For reference, here are my configurations and general operation settings
> when in C6.
> AF GAIN = high. (I'm thinking maybe to set it low)
> AF LIM 20
> AGC DCY SOFT
> AGC HLD 0.30
> AGC PLS NOR
> AGC SLP 0
> AGC THR 8
> AGC-F 120
> AGC-S 020
> SER NUM 1148
> RX EQ 1 -16
> RX EQ 2 -16
> RX EQ 3 0
> RX EQ 4 +6
> RX EQ 5 +6
> RX EQ 6 0
> RX EQ 7 -10
> RX EQ 8 -16
>
> When operating, ATT is ALWAYS ON. I don't think I ever took it off
> except maybe when 15 was dead. PRE never on.
>
> RF gain - all over the lot - say between 9 and 3. When there were lots
> of big signals I'd crank it back and then forget to turn it up again and
> would CQ in the face of weak callers :-(
>
> AF Gain - all over the lot too.
>
> I have 250, 400, 1000 and 2.7 kHz filters.
>
> DSP _usually_ in the 500 - 700 range, sometimes a little wider,
> sometimes a little narrower. I don't think I ever went below 300 Hz.
>
> AFX never on. I don't' like it but it might be interesting to try.
> I use Bose QC2 headphones.
> I wear hearing aids.
>
> Most mods have been done to the K3s including the stiffeners on the
> synthesizers and I have swapped out the DSP boards. I have not done the
> HAGC mod.
>
> 73,
> Fred KE7X
>
> Fred Cady
> fcady at ieee dot org
>

Fabio Mantovani

Re: K3 hardware AGC experiment shows promise

In reply to this post by Barry N1EU

Nice idea, Barry, but probably continuously flashing something on the
display should be an easier solution from a firmware mod point of view.
Maybe flashing the 'F' of the AGC on the display, or something similar.
That should be straightforward and doesn't require any physical
modification to the rig.

Ciao,
Fabio
IZ4AFW - NZ1W - HI9/IZ4AFW

Il 05/12/2011 13.29, Barry N1EU ha scritto:

> I think it would be informative to monitor whether the HAGC is indeed
> kicking in during the variety of pileup mush type events not involving very
> strong signals in the passband.
>
> For example, could a very visible LED be set up external to the rig that
> would flash when HAGC kicks in? A few of us could operate like this in an
> upcoming contest (e.g., next weekend 10M contest) and confirm whether
> there's correlation between HAGC and pileup mush.
>
> Barry N1EU

K5WA

Re: K3 AGC Mush

In reply to this post by David Gilbert

I really can't agree with the mush comment. I've just returned from ZF1A
where we put almost 8000 Qs in the log over the CQWW CW weekend. I took my
K3 and was able to evaluate it against the station's existing TS-850 since
we were M/S and rotated positions. In my opinion, the 850 WAS mushy and the
K3 was very clear however, K6AM, our host (who is a VERY serious contester),
prefers the 850 since he has been using it for 10 years. He also owns 4 K3s
but didn't bring them on the trip since the 850s "live" in Cayman and he
brought many pounds of other equipment. Personal preference plays a huge
part of this discussion. In this case, K6AM feels like his hearing is
limited to a frequency range of 6-7K while mine is still near 20K. Maybe
that is part of the puzzle.

We regularly saw the 10 minute QSO rate meter in the 300 range and topped
400 occasionally. I loved the way the K3 was able to plow through the
pileups which were calling us and work through them as fast as possible.
The only time I heard mush on the K3 was when we had worked down the pileup
and only had very low strength guys all calling on the same frequency (the
packet/reverse beacon spotting phenomenon). These must have been micro-watt
QRP'ers or stations with minimal/indoor antennas. I had my AGC on and
didn't have any time to try multiple settings but I am extremely happy with
the K3's receiver and think it is in the high end competition grade for me.

I am sending Eric my configuration file as he requested in case he is able
to find an improvement but I will be amazed if one can be found. I've
always been extremely happy with Elecraft's commitment and motivation to
exceed expectations but they have already exceeded mine as it is. ;-)

73,
Bob K5WA

>>>>>>>>>
This has been a very real problem for serious contesters and is the
number one dissatisfaction I have with the K3 ... and with Elecraft.

Multiple low level CW signals within a narrow passband simply turn to
mush and are very difficult to distinguish. I use the bare minimum AGC
settings in an attempt to cope since turning AGC completely off during a
contest can be painful to both the ears and the K3 itself (as those who
have had to replace their audio ICs can attest) but that often does not

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Bill W4ZV

Re: K3 AGC Mush

K5WA wrote

In this case, K6AM feels like his hearing is
limited to a frequency range of 6-7K while mine is still near 20K. Maybe
that is part of the puzzle.

Not likely unless you can hear the 12k artifact (solved with the LPF upgrade for the DSP). Which reminds me...someone previously asked whether the LPF or the full DSP was necessary. The LPF alone solves the 12k artifact issue (if your hearing is good enough to hear it) and the full DSP board exchange adds extended low frequency response...mainly for ESSB. So it really depends on your situation. In all honesty, for my use, I cannot tell any difference in the 5 different K3s I've had (2 with the factory updated DSP and 3 without).

It certainly is a mystery why some experience the mush problem and others do not. Luckily I'm in the latter camp but I'm watching with interest.

73, Bill W4ZV

David Gilbert

Re: K3 AGC Mush ... or "blur"

In reply to this post by K5WA

"The only time I heard mush on the K3 was when we had worked down the
pileup and only had very low strength guys all calling on the same
frequency (the packet/reverse beacon spotting phenomenon)."

Multiple low level signals close in frequency is EXACTLY the situation
that I and at least several others are concerned about. I don't notice
the problem on stronger signals either, and my low level hearing is
still pretty good. Operating from ZF-land where you almost always have
somebody strong calling you is not the typical situation many of the
rest of us experience from our home QTH's, and I would therefore expect
that you are less likely to experience the problem. Great sensitivity
and dynamic range are less useful if what you hear cannot be deciphered.

By the way, it has been pointed out to me that "mush" may not be the
best descriptor for what I hear, and I agree with that. I think "blur"
might be a better term. When the problem shows up I can distinguish the
individual tones (the signals are not dead zero beat) but the crispness
of the keying disappears. It's as if something is filling in the spaces
between the keying elements, and I tend to believe that the culprits are
the sum/difference products of other nearby signals that happen to
overlap the signal I'm trying to copy.

73,
Dave AB7E

On 12/5/2011 8:34 AM, K5WA wrote:

> I really can't agree with the mush comment. I've just returned from ZF1A
> where we put almost 8000 Qs in the log over the CQWW CW weekend. I took my
> K3 and was able to evaluate it against the station's existing TS-850 since
> we were M/S and rotated positions. In my opinion, the 850 WAS mushy and the
> K3 was very clear however, K6AM, our host (who is a VERY serious contester),
> prefers the 850 since he has been using it for 10 years. He also owns 4 K3s
> but didn't bring them on the trip since the 850s "live" in Cayman and he
> brought many pounds of other equipment. Personal preference plays a huge
> part of this discussion. In this case, K6AM feels like his hearing is
> limited to a frequency range of 6-7K while mine is still near 20K. Maybe
> that is part of the puzzle.
>
> We regularly saw the 10 minute QSO rate meter in the 300 range and topped
> 400 occasionally. I loved the way the K3 was able to plow through the
> pileups which were calling us and work through them as fast as possible.
> The only time I heard mush on the K3 was when we had worked down the pileup
> and only had very low strength guys all calling on the same frequency (the
> packet/reverse beacon spotting phenomenon). These must have been micro-watt
> QRP'ers or stations with minimal/indoor antennas. I had my AGC on and
> didn't have any time to try multiple settings but I am extremely happy with
> the K3's receiver and think it is in the high end competition grade for me.
>
> I am sending Eric my configuration file as he requested in case he is able
> to find an improvement but I will be amazed if one can be found. I've
> always been extremely happy with Elecraft's commitment and motivation to
> exceed expectations but they have already exceeded mine as it is. ;-)
>
> 73,
> Bob K5WA
>
>

wayne burdick

Re: K3 AGC Mush ... or "blur"

Administrator

David,

Does turning AGC off (but leaving RF GAIN at max) ever "un-blur" the
signals?

Wayne
N6KR

On Dec 5, 2011, at 9:39 AM, David Gilbert wrote:

>
> "The only time I heard mush on the K3 was when we had worked down the
> pileup and only had very low strength guys all calling on the same
> frequency (the packet/reverse beacon spotting phenomenon)."
>
>
> Multiple low level signals close in frequency is EXACTLY the situation
> that I and at least several others are concerned about.

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David Gilbert

Re: K3 AGC Mush ... or "blur"

To be honest, I've never tried that very often. The one or two times I
have done so (AGC off, RF Gain at max) have not been pleasant
experiences. The only time I get a pileup of weak signals is working
Europe from here in Arizona, and that means I have to point through some
very loud signals on the East Coast ... it only takes one of them to
cross my passband to teach me a lesson.

If I get the chance during the upcoming ARRL 10m contest I'll give it
another try. I'll also try to record the entire contest to see if I can
come up with a decent sound clip.

73,
Dave AB7E

On 12/5/2011 10:57 AM, Wayne Burdick wrote:

> David,
>
> Does turning AGC off (but leaving RF GAIN at max) ever "un-blur" the
> signals?
>
> Wayne
> N6KR
>
>
> On Dec 5, 2011, at 9:39 AM, David Gilbert wrote:
>
>>
>> "The only time I heard mush on the K3 was when we had worked down the
>> pileup and only had very low strength guys all calling on the same
>> frequency (the packet/reverse beacon spotting phenomenon)."
>>
>>
>> Multiple low level signals close in frequency is EXACTLY the situation
>> that I and at least several others are concerned about.
>
>
>

Peter Wollan-2

Re: K3 hardware AGC experiment shows promise (& KE7X config)

In reply to this post by Cady, Fred

Fred's configuration struck me as quite surprising. With DSP at
5-700, his K3 would be using the 1000 kHz roofing filter, so there
would be a substantial frequency range blocked only by the DSP. And
ATT on -- why would this be attractive? I'd think to hear weak
signals close together, you'd turn off ATT, turn up RF gain, and
squeeze down to a narrow roofing filter. Wouldn't that make the
signals sharper and more legible?

I wonder if this choice of operating settings is the reason not
everyone hears the mushy effect.

Peter W0LLN

On Mon, Dec 5, 2011 at 7:09 AM, Cady, Fred <[hidden email]> wrote:

> When operating, ATT is ALWAYS ON. I don't think I ever took it off
> except maybe when 15 was dead. PRE never on.
>

> I have 250, 400, 1000 and 2.7 kHz filters.
>
> DSP _usually_ in the 500 - 700 range, sometimes a little wider,
> sometimes a little narrower. I don't think I ever went below 300 Hz.
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John Harper AE5X

Re: K3 AGC Mush ... or "blur"

In reply to this post by David Gilbert

>Multiple low level signals close in frequency is EXACTLY the situation
>that I and at least several others are concerned about. I don't notice

Curiousity is getting the best of me...what transceiver(s) *don't* exhibit this problem and allow
individual discernment of multiple weak signals near zero beat w/ each other? To a newbie
contester like myself, it almost seems a herculean expectation...

I'm mainly asking because I think our expectations of the K3 are based largely on what we
migrated to the K3 from.

John Harper
http://www.ae5x.com/blog

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Cady, Fred

Re: K3 hardware AGC experiment shows promise (& KE7Xconfig)

In reply to this post by Peter Wollan-2

I wish I had a 700 Hz filter because I like the DSP in the 400-700
region. My reason for this is that when a narrower filter is in use, it
tends to have many signals with about the same tone. At least for my
hearing, I need and like to have a spectra of audio signals. Sometimes I
get the lower tone ones and sometimes the higher ones. Also,
notwithstanding the "reverse beacon" phenomenon, there are usually
callers who are off frequency enough that a narrow filter will miss
them.
Incidentally, some of us suspect the reverse beacon spots are not the
issue that people think. We observed the pileups got much bigger when
clusters spots showed up. We suspect the RBN spots are used by
contesters and general dxers are still using and favoring the DX
clusters.

Fred Cady
fcady at ieee dot org

> -----Original Message-----
> From: [hidden email] [mailto:elecraft-
> [hidden email]] On Behalf Of Peter Wollan
> Sent: Monday, December 05, 2011 11:45 AM
> To: Elecraft Reflector
> Subject: Re: [Elecraft] K3 hardware AGC experiment shows promise (&
> KE7Xconfig)
>
> Fred's configuration struck me as quite surprising. With DSP at
> 5-700, his K3 would be using the 1000 kHz roofing filter, so there
> would be a substantial frequency range blocked only by the DSP. And
> ATT on -- why would this be attractive? I'd think to hear weak
> signals close together, you'd turn off ATT, turn up RF gain, and
> squeeze down to a narrow roofing filter. Wouldn't that make the
> signals sharper and more legible?
>
> I wonder if this choice of operating settings is the reason not
> everyone hears the mushy effect.
>
> Peter W0LLN
>
>
> On Mon, Dec 5, 2011 at 7:09 AM, Cady, Fred <[hidden email]>
> wrote:
>
> > When operating, ATT is ALWAYS ON. I don't think I ever took it off
> > except maybe when 15 was dead. PRE never on.
> >
>
> > I have 250, 400, 1000 and 2.7 kHz filters.
> >
> > DSP _usually_ in the 500 - 700 range, sometimes a little wider,
> > sometimes a little narrower. I don't think I ever went below 300 Hz.
> ______________________________________________________________
> 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

Cady, Fred

Re: K3 hardware AGC experiment shows promise

In reply to this post by wayne burdick

Should we call ordering to have a cap or two sent out?

Fred Cady
fcady at ieee dot org

1234