Regarding the K3 and high QRN levels

[Don Wilhelm-4]

Jim,

"Riding the RF Gain" is not necessary in the K3 nor any other modern
receiver.
However, reducing the RF Gain to the point where the noise level on the
band is reduced to a tolerable level helps a lot with operator comfort
while tuning.  Yes, switch to another band or another antenna and that
optimum setting will be different.  AGC does not discriminate between a
bunch of signals on a band and the atmospheric noise that is coming in
from the antenna.

73,
Don W3FPR

Jan Erik Holm wrote:

> Hmmm...that must be AGC, AFAIK my K3 does have AGC and it works!
> "Riding the RF" was done back in the 50´ties.
>
> Ahmmmmm, you don´t mean to tell me that "riding the RF" is needed
> on a "super duper 2000 century CPU DSP whiz bang" design?
> If so we aren´t doing any progress here, by golly we are walking
> backwards
>
> Jim SM2EKM
>  
>

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[Nate Bargmann]

Thanks to all who have replied.  You have helped me learn more about the
K3 and it's capabilities.

73, de Nate >>

--

"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://n0nb.us/index.html
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[Gary Gregory]

Nate,

Whilst the K3 may not be the 'Holy Grail', I have owned enough different HF
transceivers to know it is the closest yet to achieving that goal.

It does take time to learn the capabilities of any excellent quality
transceiver and the K3 is no exception, but over time you do learn how to
use the many tools Elecraft have placed in the K3 and it has been a learning
curve for me and when I now operate 'other' manufacturers equipment I am
unable to find any of them capable of producing the quality of signals that
I have become accustomed too.

Add to the above my hearing issues, (Tinnitus) and the difference is truly
remarkable in my case.

The assistance provided by posters on the reflector is an added bonus.

73's
Gary

On Sat, Jul 10, 2010 at 8:12 AM, Nate Bargmann <[hidden email]> wrote:

> Thanks to all who have replied.  You have helped me learn more about the
> K3 and it's capabilities.
>
> 73, de Nate >>
>
> --
>
> "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://n0nb.us/index.html
> ______________________________________________________________
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> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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> Please help support this email list: http://www.qsl.net/donate.html
>

--
Gary
VK4FD - Motorhome Mobile
http://www.qsl.net/vk4fd/
K3 #679
For everything else there's Mastercard!!!
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[Guy, K2AV]

AGC is instant and dynamic, and does not vary RF gain, PRE/ATT settings
which are static unless the user changes them. RF gain, PRE, and ATT result
in numeric "advice" to the CPU, rather than being in direct control of a
circuit or device as in an analog receiver.  The CPU in turn drives the
actual circuit devices from it's many outputs.  There are many uses for this
indirect linking.

At issue is that the main smart AGC is digital signal processing, and is
*AFTER* the analog to digital conversion (ADC).  The RF gain (which is
really IF gain), PRE and ATT are before the ADC, and improperly setting
those can squeeze the noise into the high numerical range in the conversion
or even engage the defensive hardware AGC which is better off not being
engaged.  The defensive AGC is analog, has no smarts, and unfortunately must
reduce signal-to-noise in doing its job of preventing ADC input overload.

Those who understand how the rig works will throttle back the pre-digital
controls to where noise is at most moderately loud to obtain best operation
of digital features.

What I am suggesting is that in an "AUTO" novice mode a slow (rate of human
turning the RF gain) throttling back can be set (and then left alone) by the
radio for those who are not into the theory and do not recognize the source
of their complaints as being caused/worsened by their misadjustment of RF
gain, PRE and ATT.

Leaving PRE on and RF gain at max on all bands regardless causes the digital
AGC to increase or reduce the noise to the same level as the wanted signal
in pauses.  This reduces the effectiveness of the NR algorithms.

Those who ride their own RF gains would not be using this.

73, Guy.

On Fri, Jul 9, 2010 at 12:37 PM, Wes Stewart <[hidden email]> wrote:

> That sounds amazingly like automatic gain control, something I thought you
> "ride the r-f gain control" types studiously avoided.
>
>
> --- On *Fri, 7/9/10, Guy Olinger K2AV <[hidden email]>* wrote:
>
>
> Or, perhaps, sinisterly, simply make this happen in the firmware
> without telling anyone.
>
>
>

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[n7ws]

I'm sorry, but you can't have it both ways.



"RF" (i-f) gain as implemented in the K3 operates on the post-filter
(8 MHz) i-f amplifier.  The control voltage is derived at least two
(perhaps three) ways.



The post 2nd mixer i-f amplifier (15 KHz) output is detected and if a threshold
is reached, so-called hardware AGC is applied to the post-filter
amplifier.  The manual i-f gain control is derived from an encoder,
processed by the DSP and summed to the same post-filter amplifier.  If I
remember what Lyle told me the last time I saw him, there is also a
contribution to this control voltage from the signal processing DSP.  I
could be mistaken on this last point, but no matter, for the sake of this
discussion it's immaterial.



So as far as the 8 MHz if amplifier is concerned, it can't tell manual r-f gain
from hardware AGC.  So when you worry about AGC degrading SNR (it does) a
reduction in i-f gain does exactly the same thing!



In fact, as I demonstrated to Lyle over a year ago, before the "R-F gain
calibration" routine, my K3 suffered noticeable SNR degradation even on
S9+50 dB signals, with the slightest engagement of the "r-f" gain
control.  This is because of the wacky gain control characteristics of the
FET(s), which can have Gm variations of 2:1, device-to-device.



I submit that a modern DSP radio with all of the "smarts" this
suggests, should not even need an r-f (or i-f) gain control.  I've used
spectrum analyzers for over 30 years (even before computer control) that slaved
the input attenuator and the i-f gain control to maximize dynamic range without
overloading the front-end mixer. If you uncoupled the controls, the test for
overload was to change the input attenuator 10 dB and see if the display
changed 10 dB.  If it was less than 10 dB then the mixer was in
compression.



If this trivial calculation can't be made in a DSP radio, then I want an analog
receiver back.



To be sure, AGC development isn't trivial, particularly with the latency that
seems to be associated with DSP.  (I'm not a digital guy, so I'm guessing
here)   But even in analog receivers, group delay is an issue with
control loop stability.  In a homebrew received I did in the 70's I had to
pick off i-f for AGC detection before the tail-end-of-the-if-crystal filter to
stabilize the loop.  But with attack time set by i-f and decay time set by
audio, it worked flawlessly.



I know it can be done digitally, if my TS-870 is any measure.  I never touch the manual gain control on that
radio (or my K3 for that matter.)  If a
human has to intervene, there is something wrong with the ACG design.

 

Wes

--- On Fri, 7/9/10, Guy Olinger K2AV <[hidden email]> wrote:
AGC is instant and dynamic, and does not vary RF gain, PRE/ATT settings which are static unless the user changes them. RF gain, PRE, and ATT result in numeric "advice" to the CPU, rather than being in direct control of a circuit or device as in an analog receiver.  The CPU in turn drives the actual circuit devices from it's many outputs.  There are many uses for this indirect linking. 


At issue is that the main smart AGC is digital signal processing, and is *AFTER* the analog to digital conversion (ADC).  The RF gain (which is really IF gain), PRE and ATT are before the ADC, and improperly setting those can squeeze the noise into the high numerical range in the conversion or even engage the defensive hardware AGC which is better off not being engaged.  The defensive AGC is analog, has no smarts, and unfortunately must reduce signal-to-noise in doing its job of preventing ADC input overload.


Those who understand how the rig works will throttle back the pre-digital controls to where noise is at most moderately loud to obtain best operation of digital features. 

What I am suggesting is that in an "AUTO" novice mode a slow (rate of human turning the RF gain) throttling back can be set (and then left alone) by the radio for those who are not into the theory and do not recognize the source of their complaints as being caused/worsened by their misadjustment of RF gain, PRE and ATT. 


Leaving PRE on and RF gain at max on all bands regardless causes the digital AGC to increase or reduce the noise to the same level as the wanted signal in pauses.  This reduces the effectiveness of the NR algorithms.


Those who ride their own RF gains would not be using this. 

73, Guy.





     
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[The Smiths]

And yet I find everything works better when I pot down on the RF gain... hmmm
 

> Date: Fri, 9 Jul 2010 20:16:37 -0700
> From: [hidden email]
> To: [hidden email]
> CC: [hidden email]
> Subject: Re: [Elecraft] Regarding the K3 and high QRN levels
>
>
>
>
>
> I'm sorry, but you can't have it both ways.
>
>
>
> "RF" (i-f) gain as implemented in the K3 operates on the post-filter
> (8 MHz) i-f amplifier.  The control voltage is derived at least two
> (perhaps three) ways.
>
>
>
> The post 2nd mixer i-f amplifier (15 KHz) output is detected and if a threshold
> is reached, so-called hardware AGC is applied to the post-filter
> amplifier.  The manual i-f gain control is derived from an encoder,
> processed by the DSP and summed to the same post-filter amplifier.  If I
> remember what Lyle told me the last time I saw him, there is also a
> contribution to this control voltage from the signal processing DSP.  I
> could be mistaken on this last point, but no matter, for the sake of this
> discussion it's immaterial.
>
>
>
> So as far as the 8 MHz if amplifier is concerned, it can't tell manual r-f gain
> from hardware AGC.  So when you worry about AGC degrading SNR (it does) a
> reduction in i-f gain does exactly the same thing!
>
>
>
> In fact, as I demonstrated to Lyle over a year ago, before the "R-F gain
> calibration" routine, my K3 suffered noticeable SNR degradation even on
> S9+50 dB signals, with the slightest engagement of the "r-f" gain
> control.  This is because of the wacky gain control characteristics of the
> FET(s), which can have Gm variations of 2:1, device-to-device.
>
>
>
> I submit that a modern DSP radio with all of the "smarts" this
> suggests, should not even need an r-f (or i-f) gain control.  I've used
> spectrum analyzers for over 30 years (even before computer control) that slaved
> the input attenuator and the i-f gain control to maximize dynamic range without
> overloading the front-end mixer. If you uncoupled the controls, the test for
> overload was to change the input attenuator 10 dB and see if the display
> changed 10 dB.  If it was less than 10 dB then the mixer was in
> compression.
>
>
>
> If this trivial calculation can't be made in a DSP radio, then I want an analog
> receiver back.
>
>
>
> To be sure, AGC development isn't trivial, particularly with the latency that
> seems to be associated with DSP.  (I'm not a digital guy, so I'm guessing
> here)   But even in analog receivers, group delay is an issue with
> control loop stability.  In a homebrew received I did in the 70's I had to
> pick off i-f for AGC detection before the tail-end-of-the-if-crystal filter to
> stabilize the loop.  But with attack time set by i-f and decay time set by
> audio, it worked flawlessly.
>
>
>
> I know it can be done digitally, if my TS-870 is any measure.  I never touch the manual gain control on that
> radio (or my K3 for that matter.)  If a
> human has to intervene, there is something wrong with the ACG design.
>
>  
>
> Wes
>
> --- On Fri, 7/9/10, Guy Olinger K2AV <[hidden email]> wrote:
> AGC is instant and dynamic, and does not vary RF gain, PRE/ATT settings which are static unless the user changes them. RF gain, PRE, and ATT result in numeric "advice" to the CPU, rather than being in direct control of a circuit or device as in an analog receiver.  The CPU in turn drives the actual circuit devices from it's many outputs.  There are many uses for this indirect linking.  
>
>
> At issue is that the main smart AGC is digital signal processing, and is *AFTER* the analog to digital conversion (ADC).  The RF gain (which is really IF gain), PRE and ATT are before the ADC, and improperly setting those can squeeze the noise into the high numerical range in the conversion or even engage the defensive hardware AGC which is better off not being engaged.  The defensive AGC is analog, has no smarts, and unfortunately must reduce signal-to-noise in doing its job of preventing ADC input overload.
>
>
> Those who understand how the rig works will throttle back the pre-digital controls to where noise is at most moderately loud to obtain best operation of digital features.  
>
> What I am suggesting is that in an "AUTO" novice mode a slow (rate of human turning the RF gain) throttling back can be set (and then left alone) by the radio for those who are not into the theory and do not recognize the source of their complaints as being caused/worsened by their misadjustment of RF gain, PRE and ATT.  
>
>
> Leaving PRE on and RF gain at max on all bands regardless causes the digital AGC to increase or reduce the noise to the same level as the wanted signal in pauses.  This reduces the effectiveness of the NR algorithms.
>
>
> Those who ride their own RF gains would not be using this.  
>
> 73, Guy.
>
>
>
>
>
>
> ______________________________________________________________
> 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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[Edward R Cole]

My first experience with DSP was using my FT-847.  It is OK but not
spectacular.  I mainly operate VHF+ and mostly eme so that is a
different thing than HF.  The FT-847 is audio DSP so that limits it
right away.  DSP filters are fixed in CW: 400-200-100-25 Hz.  NR
worked OK on SSB.  NB was not worth turning on.

The K3 has IF DSP so a different animal.  I like the versatility but
that means a steep learning curve to discover what works, when and
where.  I am impressed with NR on HF SSB.  Having a combination of
roofing filters and DSP filtering really works nice when digging out
super weak signals.  The NB is pretty good on impulse noise (way
better than the FT-847).

DSP technology is advancing quickly.  My hearing aids are
digital.  They separate the audio spectrum into 22 channels and have
echo cancellation and four NR routines including
noise-cancellation.  So I guess I will always have DSP when listening
to my K3 (or anything) ;-) .  As the sampling rate increases for DSP
the closer it will be to analog hearing.  My hearing is -30dB so I
must use hearing aids.  They are predicting in 10-15 years implant
DSP on the audio nerve will render hearing loss completely cured...in
fact those with it will hear better than natural hearing (ahh, bionic ears!).

This applies to radio DSP in the same fashion.

The K3 has versatility that I have not begun to use (and not just
DSP).  I think as one gains experience in using DSP in more
situations it will grow on you.

73, Ed - KL7UW

------------------------------

Message: 18
Date: Thu, 08 Jul 2010 19:11:39 -0400
From: Don Wilhelm <[hidden email]>
Subject: Re: [Elecraft] Regarding the K3 and high QRN levels
To: [hidden email]
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Tom,

I do agree that a specially tuned analog system will provide better
results for the specific task that it is tuned for than a digital system
any day.
The advantage of digital is that it can be made "almost as good" while
being more flexible through the use of computing power.
Your desires tend toward weak signal CW operation on the low bands - we
all know that.  But an analog system tuned to those needs would not be
ideal for ease of operation in say a ragchewing SSB situation - for one
thing the filters are too narrow :-) .
The major advantage offered by DSP is the ability to change the
filtering with the turn of a knob, and process the modulation and
demodulation tasks with computational algorithms rather than changing
the hardware - tailoring the algorithms to each task.  Is it as good as
analog tuned for a specific task?  NO - but it is usually better than a
general purpose analog system that attempts to be "everything to
everybody".  The equivalent flexibility with the same degree of
"best-ness" would be cost prohibitive if attempted in analog.

73,
Don W3FPR



73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
EME: 144-QRT*, 432-100w, 1296-QRT*, 3400-fall 2010
DUBUS Magazine USA Rep [hidden email]
======================================
*temp

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[Guy, K2AV]

The defensive hardware AGC is hardware AGC because you can see the entire
circuit for this defensive AGC in analog components.  It cannot be turned
off.  It is an AGC that in all circumstances would be better if you didn't
need to use it, though this is clearly not possible in some circumstances.
This is only one of various reasons for using the narrowest roofing filter
that fits the mode and usage.

I could call hardware AGC simple-*ssed AGC, because it is, and it has only
one purpose: don't overdrive the d*mned analog to digital converter (ADC).
Hardware AGC seems more polite. ADC-defensive is more specific.

DSP AGC is entirely done in algorithm in the number soup bit bucket.

The degradation of NR performance occurs when the ambient noise level is
allowed to hit the ADC at a high level, so that both the noise and desired
signals are at the same level going into the ADC, with the defensive
hardware AGC acting as the leveling device.  The follow-on digital
algorithms then have to accept as fact that the noise and the desired signal
are now the same level.  Perhaps with an ADC with another 30 or 40 db range,
and similar increases in non-military cost processors are available, a
defensive hardware AGC will not be needed.

The manual solution to the quandary of the prior paragraph is to turn off
PRE, perhaps turn on ATT, and perhaps reduce the RF gain pot as well until
the ambient noise is only moderate at the K3 output.  As clear as this might
seem to some, attempts to correctly relate a "roaring noisy" K3 to
PRE/ATT/RFgain settings for a band have often not been understood.

PRE/ATT/RFgain are not dynamic adjustments, they don't vary in millisecond
time ranges as found in hardware AGC.  They vary at most at hand-twiddle
speeds as they are manual.  When the PRE/ATT/RFgain have been turned down so
that ambient noise is in the LOW range at the ADC, then following digital
algorithms have true information to work with, that has not been compressed
by the hardware AGC.  The DSP's "AGC" can do the stuff that can't be done
with simple circuits.

>From emails it is clear that proper manual reduction of PRE/ATT/RFgain to
suit band and conditions is not catching on in a significant customer
slice.  My suggestion is to take these users at face value, that they want
the setting of PRE/ATT/RFgain done automatically for best performance.

If someone insists on calling that AGC, then there would be *THREE* AGC's.
Hardware ADC-defensive AGC, digital level management in DSP algorithms, and
a third, crawl-speed RF string management AGC.

I'm thinking that the DSP can tell the difference between noise and discrete
signal. It therefore can over a period of time (a second or two, or five or
ten?) determine the best setting of PRE/ATT/RFgain and slowly engage the
preamp, attenuator and set the resting gain of the post filter IF ampl based
on that determination, rather than manual input.

This latter automatic mode for RF string management could be engaged by
reducing RFgain to minimum. To get out of it the user could advance the
RFgain. At the point matching the automatic setting, the manual control
would re-engage.  The PRE/ATT settings would be left as is, because those
would probably be correct.  But they would follow the buttons if depressed.

73, Guy.



On Fri, Jul 9, 2010 at 11:16 PM, Wes Stewart <[hidden email]> wrote:

> I'm sorry, but you can't have it both ways.
>
> "RF" (i-f) gain as implemented in the K3 operates on the post-filter (8
> MHz) i-f amplifier.  The control voltage is derived at least two (perhaps
> three) ways.
>
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