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K3 in a cw pileup - needs work

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Mike Reublin

Re: K3 DSP AGC Question

The Yamaha CM-500, recommended by quite a few here, is 120 ohms, right?
So cranking up the AF results is less than optimum operation?

73,
Mike, NF4L

Lyle Johnson wrote:

>> There IS something entirely separate with the headphone audio and HI-Z
>> headsets, high volume levels, maybe a sharp saturation point, and
>> mush, just haven't nailed it yet.
>>
>
> Note that the headphone audio path of the K3 is designed for 32-ohm and
> lower headphone impedances. Higher impedance phones provide less audio
> for a given transducer efficiency. Cranking up the AF gain to
> compensate can lead to clipping-related distortion.
>
> 73,
>
> Lyle KK7P
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>

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Guy, K2AV

Re: K3 DSP AGC Question

In reply to this post by KK7P

OK, except a lot of people have these 400 and 600 ohm headsets by
well-known makers. People are blaming it on everything from the phases
of the moon to the neighbor's dog. It would be good to have that
cleanly targeted.

What's the recommended workaround or is there a workaround? Maybe a
high impedance headphone dongle kit that terminates the stereo speaker
audio in 8 ohms and has both headphone jacks?

73, Guy.

On Mon, Feb 8, 2010 at 2:00 PM, Lyle Johnson <[hidden email]> wrote:

>
>> There IS something entirely separate with the headphone audio and HI-Z
>> headsets, high volume levels, maybe a sharp saturation point, and
>> mush, just haven't nailed it yet.
>
> Note that the headphone audio path of the K3 is designed for 32-ohm and
> lower headphone impedances. Higher impedance phones provide less audio for
> a given transducer efficiency. Cranking up the AF gain to compensate can
> lead to clipping-related distortion.
>
> 73,
>
> Lyle KK7P
>

Ken Kopp-3

Heil headphone level

I'm likely only adding to the "noise" here, but I have two
Heil HS's that work well with my K3 and can deliver -far-
more audio than my 72 year old ears can handle with the
AF gain parameter set for "LO".

73! Ken Kopp - K0PP
[hidden email]
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KK7P

Re: K3 DSP AGC Question

In reply to this post by Guy, K2AV

I didn't mean to stir up yet another controversy. I use Heil Proset
with my K3 and they work just fine, as do my Yamaha CM500.
The K3 can easily drive high-impedance headphones.

My point was simply that *if* you have to crank up AF gain to the point
of distortion to get sufficient headphone volume, and *if* you are using
high-impedance headphones, *then* the problem *may* be related to the
headphone impedance.

73,

Lyle KK7P

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K6LMP

Re: K3 DSP AGC Question

Ummm, if this is a real issue for some operators (and not a theoretical issue), it would seem the problem could easily be resolved with an audio transformer.

RadioShack sells one for $2.99. They don't publish the specs in enough detail to tell for sure, but it has a number of taps on the secondary, and would appear to be able to transform the impedance of most headphones into the K3's "sweet spot."

Am I missing something here? a small project box with the transformer enclosed and phone jacks in and out ought to do the trick.

Lew K6LMP

On Feb 8, 2010, at 12:45 PM, Lyle Johnson wrote:

> I didn't mean to stir up yet another controversy. I use Heil Proset
> with my K3 and they work just fine, as do my Yamaha CM500.
> The K3 can easily drive high-impedance headphones.
>
> My point was simply that *if* you have to crank up AF gain to the point
> of distortion to get sufficient headphone volume, and *if* you are using
> high-impedance headphones, *then* the problem *may* be related to the
> headphone impedance.
>
> 73,
>
> Lyle KK7P
>
>
>
>
> ______________________________________________________________
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Barry N1EU

Re: K3 DSP AGC Question

In reply to this post by Mike K2MK

Mike K2MK wrote

I was very disappointed to read your post. I purchased a Proset headset directly from Elecraft when I bought my K3. According to Heil this headset has an impedance of 200 ohms. Is that why I have to plug my headphones into the rear speaker jack to get sufficient audio output from them? Why would you folks sell a headset that does not complement the K3? I am really disappointed.

I routinely use a 200-ohm Pro Set for ssb plugged into the headphone jack and it works like a charm.

73,
Barry N1EU

David Christ

What is high impedance

In reply to this post by Guy, K2AV

After Lyle's comment (reproduced below), there has been been concern
expressed about headsets of 120 to 600 ohms. A close reading of
Lyle's words indicates that higher impedance is only a problem if
there is a need to increase the AF gain too much. As long as you
don't have to crank the AF gain way up there shouldn't be a problem.

I think there is also some confusion about what high impedance means.
The common WW II aircraft headset came in two versions High Z at
4000 ohms and Low Z at 600 ohms. By that standard 120 ohms is very
low and 600 is still low.

If your AF gain is at 3 o'clock maybe your earphones or ears have too
high an impedance.

David K0LUM

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

Note that the headphone audio path of the K3 is designed for 32-ohm and
lower headphone impedances. Higher impedance phones provide less audio
for a given transducer efficiency. Cranking up the AF gain to
compensate can lead to clipping-related distortion.

73,

Lyle KK7P
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Grant Youngman

Re: K3 DSP AGC Question

In reply to this post by Barry N1EU

>>
>> I was very disappointed to read your post. I purchased a Proset headset
>> directly from Elecraft when I bought my K3. According to Heil this headset
>> has an impedance of 200 ohms. Is that why I have to plug my headphones
>> into the rear speaker jack to get sufficient audio output from them? Why
>> would you folks sell a headset that does not complement the K3? I am
>> really disappointed.

There are two factors here. One is impedance. (The impedance actually presented by a headphone is frequency dependent and can vary widely from the "nominal" value). The other is sensitivity.

I regularly use 250 ohm headphones on the K3 with no issues whatsoever. Why? They require very little drive to reach an acceptable output level. So even given their relatively high Z (compared to 32 ohms) it isn't necessary to drive the output stage of the K3 into clipping or high distortion levels to get plenty of good audio.

I have a set of high end audiophile headphones with 62 ohm Z. I don't use them on the K3 (tried them once). Why? It takes a whole lot of power (relatively) to drive them to reasonable listening levels.

Given the number of people who use Prosets and seem to like them just fine, I don't know why there would be any real concern or any reason to feel disappointment.

Grant/NQ5T
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drewko

Re: What is high impedance

In reply to this post by David Christ

For my K3 I like using Koss SprtaPro headphones. They are 60-ohms,
very light, omfortable and non-fatiguing (but "high isolation" by no
means). They are collapsible and the headband can pivot to behind head
(so you don't muss up your 'do...) Lifetime warranty. They sound
really good to me, but may have too much bass for some. I think
they're great for CW.

73,
Drew

On Mon, 08 Feb 2010 15:47:52 -0600, David K0LUM wrote:

>After Lyle's comment (reproduced below), there has been been concern
>expressed about headsets of 120 to 600 ohms. A close reading of
>Lyle's words indicates that higher impedance is only a problem if
>there is a need to increase the AF gain too much. As long as you
>don't have to crank the AF gain way up there shouldn't be a problem.
>
>I think there is also some confusion about what high impedance means.
>The common WW II aircraft headset came in two versions High Z at
>4000 ohms and Low Z at 600 ohms. By that standard 120 ohms is very
>low and 600 is still low.
>
>If your AF gain is at 3 o'clock maybe your earphones or ears have too
>high an impedance.
>
>David K0LUM
>

ab2tc

Re: K3 DSP AGC Question

In reply to this post by Grant Youngman

Hi, I use the 200 ohm Heil proset and even with the AF gain set to "LO" I have no problem getting enough audio or distortion free audio. Either there is a number of defective prosets or K3s out there because this is making no sense at all.

Knut - AB2TC

Grant Youngman wrote

<snip>
There are two factors here. One is impedance. (The impedance actually presented by a headphone is frequency dependent and can vary widely from the "nominal" value). The other is sensitivity.

I regularly use 250 ohm headphones on the K3 with no issues whatsoever. Why? They require very little drive to reach an acceptable output level. So even given their relatively high Z (compared to 32 ohms) it isn't necessary to drive the output stage of the K3 into clipping or high distortion levels to get plenty of good audio.
<snip>
Grant/NQ5T
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Guy, K2AV

Re: K3 DSP AGC Question

In reply to this post by Barry N1EU

I think some of us have reduced hearing, and crank up volume on
EVERYTHING, including TV. Ask your wives. It's probably not fair or
electronically practical to expect that kind of range in everything.
My Bose QC15's (plugged into headphone jack) would blow my head off if
I turned up the K3 AF past about 9 oclock.

On Mon, Feb 8, 2010 at 4:44 PM, Barry N1EU <[hidden email]> wrote:

>
>
> Mike K2MK wrote:
>>
>> I was very disappointed to read your post. I purchased a Proset headset
>> directly from Elecraft when I bought my K3. According to Heil this headset
>> has an impedance of 200 ohms. Is that why I have to plug my headphones
>> into the rear speaker jack to get sufficient audio output from them? Why
>> would you folks sell a headset that does not complement the K3? I am
>> really disappointed.
>>
> I routinely use a 200-ohm Pro Set for ssb plugged into the headphone jack
> and it works like a charm.
>
> 73,
> Barry N1EU
>
> --
> View this message in context: http://n2.nabble.com/K3-in-a-cw-pileup-needs-work-tp4523884p4537307.html
> Sent from the [K3] mailing list archive at Nabble.com.
> ______________________________________________________________
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W6ODJ

Re: K3 in a cw pileup - needs work

In reply to this post by Bill W4ZV

I hope people do not make the mistake of using in-the-ear earbuds with ham radios, even the K3. These in-the-ear phones like the etymotic or the shure have to be put pretty deep into the ear canal to seal and provide isolation. They are wonderful for hi-fi. I use a pair by Shure to listen to Brahms on airplanes. BUT, they take at least a few seconds to extract from your ears. If, as has been reported on this reflector several times, the radio mis-functions and puts out a very loud audio signal, your ears will be fried before you can react.

DON'T DO IT!!!!

Oliver
W6ODJ

On 7 Feb 2010, at 3:21 AM, Bill W4ZV wrote:

>
> "High isolation headphones" below means ~30 dB isolation from ambient noise.
> Heil does not make any in this range and most active noise reduction
> headphones (e.g. Bose) only have 10-15 dB. Here are some examples of what
> Barry meant:
>
> http://www.extremeheadphones.com/ex-29.html
> http://www.sennheiserusa.com/private_headphones_dj-headphones_004974
> http://www.etymotic.com/ephp/er6.aspx
>
> These are all available in the $75-100 range.
>
> 73, Bill
>
>
> Doug Turnbull wrote:
>>
>> Barry, Sorry but what do you mean by 'high isolation headphones'. Would
>> the Heil Pro-Set Plus do?
>> 73 Doug EI2CN
>>
>> -----Original Message-----
>> From: [hidden email]
>> [mailto:[hidden email]] On Behalf Of Barry N1EU
>> Sent: 07 February 2010 01:01
>> To: [hidden email]
>> Subject: Re: [Elecraft] K3 in a cw pileup - needs work
>>
>>
>>
>> Barry N1EU wrote:
>>>
>>> You need to maximize your rf/af dynamic range - that is what is going to
>>> turn that mush into a beautiful symphony of distinct signals of varying
>>> levels. What has worked well for me is AGC off (although AGC on works
>>> fine as well), high isolation headphones, and the gain throttling
>>> techniques (most important) described by K3NA, W4ZV, myself, and others.
>>>
>> Just to continue from previous post - I experienced only mush in pileup
>> reception until fully adopting this technique. High isolation headphones
>> are critical because you want to set gain such that weak signals are
>> lightly
>> heard but clearly copiable. You're maximizing the receive dynamic range
>> delivered to your ears and the high isolation means you can clearly hear
>> fainter signals without turning up the gain and squashing the dynamic
>> range
>> (and too frequently engaging AF Limiter with AGC Off).
>>
>> 73,
>> Barry N1EU
>>
>> --
>> View this message in context:
>> http://n2.nabble.com/K3-in-a-cw-pileup-needs-work-tp4523884p4527626.html
>> Sent from the Elecraft mailing list archive at Nabble.com.
>> ______________________________________________________________
>> Elecraft mailing list
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>> Post: mailto:[hidden email]
>>
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>> Please help support this email list: http://www.qsl.net/donate.html
>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>> Post: mailto:[hidden email]
>>
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>> Please help support this email list: http://www.qsl.net/donate.html
>>
>>
>
> --
> View this message in context: http://n2.nabble.com/K3-in-a-cw-pileup-needs-work-tp4523884p4528787.html
> Sent from the [K3] mailing list archive at Nabble.com.
> ______________________________________________________________
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Mike K2MK

Re: K3 DSP AGC Question

In reply to this post by Barry N1EU

Hi Barry:

I was annoyed when I first read Lyle's post. It sounded like the right hand didn't know what the left was doing. Really, why optimize the amplifier for 32 ohms and then only offer a 200 ohm headset for sale. But Lyle's further explanation was reasonable and I probably overreacted.

I know my hearing is not what it used to be. I first used the speaker jack during the ARRL 10 meter contest in Dec 08. The band was noisy so I had the NR on but there just wasn't enough volume available to pull out the barely audible stations. (Having a no gain vertical doesn't help either). There really is no good reason to keep the headphones in the speaker jack on the other bands. I just do and I keep the AF level correspondingly low.

I took note of your recent posting about the HD-280s. I put them away when I got the K3 and the Proset. But after the discussion regarding isolation I pulled them out and they have slightly greater volume then the Proset. I like the Proset because it has very comfortable ear pads. The 280 has a tighter grip on my head and the pads are a bit more rubbery. I think that's why I stayed with the Proset. But the ARRL DX contest is coming up so I think I'll give the 280s a whirl and see which I prefer.

73,

Mike K2MK

From: [hidden email]

Sent: Monday, February 08, 2010 4:44 PM

To: [hidden email]

Subject: Re: K3 DSP AGC Question

Mike K2MK wrote:

I was very disappointed to read your post. I purchased a Proset headset directly from Elecraft when I bought my K3. According to Heil this headset has an impedance of 200 ohms. Is that why I have to plug my headphones into the rear speaker jack to get sufficient audio output from them? Why would you folks sell a headset that does not complement the K3? I am really disappointed.

I routinely use a 200-ohm Pro Set for ssb plugged into the headphone jack and it works like a charm.

73,
Barry N1EU

View message @ http://n2.nabble.com/K3-in-a-cw-pileup-needs-work-tp4523884p4537307.html
To unsubscribe from Re: K3 DSP AGC Question, click here.

Jim Brown-10

High Isolation Headphones

In reply to this post by Bill W4ZV

On 2/7/2010 3:21 AM, Bill W4ZV wrote:

> "High isolation headphones" below means ~30 dB isolation from ambient noise.
> Heil does not make any in this range and most active noise reduction
> headphones (e.g. Bose) only have 10-15 dB. Here are some examples of what
> Barry meant:
>
> http://www.extremeheadphones.com/ex-29.html
> http://www.sennheiserusa.com/private_headphones_dj-headphones_004974
> http://www.etymotic.com/ephp/er6.aspx
>
> These are all available in the $75-100 range.
>

Yes. I work in pro audio, and have owned two sets Etymotic ER4 in-ear
headphones for nearly ten years. I first bought them to use in my live
recording work, where I'm mixing a jazz band in the same room with the
musicians, and they're often playing pretty loud. The isolation can be
quite good, in the 30 dB range that Bill talks about, but it depends on
how well they fit your ears. The standard fittings are quite soft, and
they happen to fit my ears very well. Every person's ears are different,
and some need custom "ear molds" from an audiologist for the ultimate
isolation.

As I've gradually slowed down my pro audio work, I've ramped up ham
radio and when I got back on the air in 2003, the Etymotics almost
immediately found their way into my ham shack. They're quite
comfortable, and I can wear them for a long time.

The real question is, ":how much isolation do you need?" When I'm
working a SSB contest, I'm very happy with the sound, comfort, and
isolation of the CM500 headset, but I haven't used it yet in a
multi-multi operation. I suspect it will perform pretty well.

73,

Jim Brown K9YC
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Joe Subich, W4TV-4

Re: K3 DSP AGC Question

In reply to this post by Guy, K2AV

> It may be a dance, but hopefully careful intelligent musing
> over the matter is convincing people that they should get the
> ambient well down in the analog-to-digital converter (ADC)
> operating range. If they do, a -99 threshold is a -109
> threshold, and further backing off RF gain can make it a -119
> or -129 threshold as far as the ADC is concerned, and
> headroom is being used for what headroom should be used for.

Perhaps one should get the ambient well down in the ADC operating
range but killing gain (adding loss) before the first mixer and
the roofing filter is not the way to do it. If you want to
better align the dynamic range of the receiver (or specifically
the ADC) to conditions, the attenuation should come in the
IF - preferably divided between the first IF and 2nd IF.

However, there would still be no apparent reason that the K3
should not be capable of sustaining an AGC threshold at least
10 db higher than currently set with AGC THR = 008 whether
that be reached with preamp on, preamp off or attenuator on.

73,

... Joe, W4TV

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Guy
> Olinger K2AV
> Sent: Monday, February 08, 2010 1:49 PM
> To: [hidden email]
> Cc: [hidden email]
> Subject: Re: [Elecraft] K3 DSP AGC Question
>
>
> It may be a dance, but hopefully careful intelligent musing
> over the matter is convincing people that they should get the
> ambient well down in the analog-to-digital converter (ADC)
> operating range. If they do, a -99 threshold is a -109
> threshold, and further backing off RF gain can make it a -119
> or -129 threshold as far as the ADC is concerned, and
> headroom is being used for what headroom should be used for.
>
> One thing for sure, there has not been a good-enough
> presentation of what is going on, and people really don't
> seem to get it. For something that is plain indisputable
> physics, people are still running PRE and max RFgain on 80
> with fast AGC, and are honestly dismayed and confused about
> the inevitable outcome, incorrectly blaming the rig for being
> natively noisy, no-work NR and NB, filter "ringing", unable
> to pull signals out of noise, and more.
>
> Maybe the variable gain by band in the MP (with a menu
> override) was really a better strategy for a default. This
> same issue dogged Orion owners, and by the chatter a lot of
> them never understood either.
>
> There IS something entirely separate with the headphone audio
> and HI-Z headsets, high volume levels, maybe a sharp
> saturation point, and mush, just haven't nailed it yet.
>
> 73, Guy.
>
> On Mon, Feb 8, 2010 at 12:01 PM, Joe Subich, W4TV
> <[hidden email]> wrote:
> >
> >
> >> Likely? I don't know.
> >
> > Likely is a better choice since raising the AGC threshold
> seems to be
> > the primary goal of much of the "PRE/ATT/RF Gain dance" we've seen
> > recently.
> >
> > The hardware AGC (HAGC) would seem to provide an ultimate limit on
> > level to the ADC - unless the ADC can't handle the
> transient peaks -
> > so a higher threshold for the DSP derived AGC would be
> helpful in many
> > ways.
> >
> > 73,
> >
> > ... Joe, W4TV
> >
> >
> >
> >
> >> -----Original Message-----
> >> From: [hidden email]
> >> [mailto:[hidden email]] On Behalf Of Lyle Johnson
> >> Sent: Monday, February 08, 2010 11:24 AM
> >> To: [hidden email]
> >> Subject: Re: [Elecraft] K3 DSP AGC Question
> >>
> >>
> >> Hello Joe!
> >> > Assuming that the threshold values have not changed in a
> major way
> >> > since Jack's measurements, would it be possible to
> extend the range
> >> > of threshold values - say to AGC THR=016 at about -80dBm
> (assuming
> >> > 2 dB per step)?
> >> >
> >>
> >> Possible? Yes.
> >>
> >> Likely? I don't know. There are a lot of side effects
> that happen
> >> when the threshold is raised...
> >>
> >> 73,
> >>
> >> Lyle KK7P
> >>
> >
> >
> > ______________________________________________________________
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> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> >
> ______________________________________________________________
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Don Wilhelm-4

Re: K3 DSP AGC Question

Joe,

Can you elaborate your reasons for this suggestion. I had come to
believe that the best situation is to place attenuation before the first
mixer to give the greatest amount of dynamic range (headroom).

Yes, I agree that the AGC Threshold could be raised in the K3 and would
be beneficial. I have felt the default of 005 was too low.

73,
Don W3FPR

Joe Subich, W4TV wrote:

> Perhaps one should get the ambient well down in the ADC operating
> range but killing gain (adding loss) before the first mixer and
> the roofing filter is not the way to do it. If you want to
> better align the dynamic range of the receiver (or specifically
> the ADC) to conditions, the attenuation should come in the
> IF - preferably divided between the first IF and 2nd IF.
>
> However, there would still be no apparent reason that the K3
> should not be capable of sustaining an AGC threshold at least
> 10 db higher than currently set with AGC THR = 008 whether
> that be reached with preamp on, preamp off or attenuator on.
>
> 73,
>
> ... Joe, W4TV
>
>
>
>
>> -----Original Message-----
>> From: [hidden email]
>> [mailto:[hidden email]] On Behalf Of Guy
>> Olinger K2AV
>> Sent: Monday, February 08, 2010 1:49 PM
>> To: [hidden email]
>> Cc: [hidden email]
>> Subject: Re: [Elecraft] K3 DSP AGC Question
>>
>>
>> It may be a dance, but hopefully careful intelligent musing
>> over the matter is convincing people that they should get the
>> ambient well down in the analog-to-digital converter (ADC)
>> operating range. If they do, a -99 threshold is a -109
>> threshold, and further backing off RF gain can make it a -119
>> or -129 threshold as far as the ADC is concerned, and
>> headroom is being used for what headroom should be used for.
>>
>> One thing for sure, there has not been a good-enough
>> presentation of what is going on, and people really don't
>> seem to get it. For something that is plain indisputable
>> physics, people are still running PRE and max RFgain on 80
>> with fast AGC, and are honestly dismayed and confused about
>> the inevitable outcome, incorrectly blaming the rig for being
>> natively noisy, no-work NR and NB, filter "ringing", unable
>> to pull signals out of noise, and more.
>>
>> Maybe the variable gain by band in the MP (with a menu
>> override) was really a better strategy for a default. This
>> same issue dogged Orion owners, and by the chatter a lot of
>> them never understood either.
>>
>> There IS something entirely separate with the headphone audio
>> and HI-Z headsets, high volume levels, maybe a sharp
>> saturation point, and mush, just haven't nailed it yet.
>>
>> 73, Guy.
>>
>> On Mon, Feb 8, 2010 at 12:01 PM, Joe Subich, W4TV
>> <[hidden email]> wrote:
>>
>>>
>>>> Likely? I don't know.
>>>>
>>> Likely is a better choice since raising the AGC threshold
>>>
>> seems to be
>>
>>> the primary goal of much of the "PRE/ATT/RF Gain dance" we've seen
>>> recently.
>>>
>>> The hardware AGC (HAGC) would seem to provide an ultimate limit on
>>> level to the ADC - unless the ADC can't handle the
>>>
>> transient peaks -
>>
>>> so a higher threshold for the DSP derived AGC would be
>>>
>> helpful in many
>>
>>> ways.
>>>
>>> 73,
>>>
>>> ... Joe, W4TV
>>>
>>>
>>>
>>>
>>>
>>>> -----Original Message-----
>>>> From: [hidden email]
>>>> [mailto:[hidden email]] On Behalf Of Lyle Johnson
>>>> Sent: Monday, February 08, 2010 11:24 AM
>>>> To: [hidden email]
>>>> Subject: Re: [Elecraft] K3 DSP AGC Question
>>>>
>>>>
>>>> Hello Joe!
>>>>
>>>>> Assuming that the threshold values have not changed in a
>>>>>
>> major way
>>
>>>>> since Jack's measurements, would it be possible to
>>>>>
>> extend the range
>>
>>>>> of threshold values - say to AGC THR=016 at about -80dBm
>>>>>
>> (assuming
>>
>>>>> 2 dB per step)?
>>>>>
>>>>>
>>>> Possible? Yes.
>>>>
>>>> Likely? I don't know. There are a lot of side effects
>>>>
>> that happen
>>
>>>> when the threshold is raised...
>>>>
>>>> 73,
>>>>
>>>> Lyle KK7P
>>>>
>>>>
>>> ______________________________________________________________
>>> 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
>>>
>>>
>> ______________________________________________________________
>> 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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David Gilbert

Re: K3 DSP AGC Question

I also think that the current max AGC threshold is too low, but I have another question. Why is it necessary for the K3 AGC to have such a sharp elbow at the point where the AGC kicks in? The Clifton Labs plots show such a sharp bend that it seems multi-signal in-band intermod is inevitable, especially with higher SLP settings. Wouldn't it be feasible, and more desirable, to have some more gradual inflection point? I would think that something like a parabolic shape would be better, and the DSP AGC is just the implementation of an algorithm, correct? I suppose that would tend to blur the distinction between different THR settings, but so what?

Maybe somebody can educate me ...

73,
Dave AB7E

------Original Mail------
From: "Don Wilhelm" <[hidden email]>
To: "Joe Subich, W4TV" <[hidden email]>,
<[hidden email]>
Sent: Wed, 10 Feb 2010 01:06:09 -0500
Subject: Re: [Elecraft] K3 DSP AGC Question

Joe,

Can you elaborate your reasons for this suggestion. I had come to
believe that the best situation is to place attenuation before the first
mixer to give the greatest amount of dynamic range (headroom).

Yes, I agree that the AGC Threshold could be raised in the K3 and would
be beneficial. I have felt the default of 005 was too low.

73,
Don W3FPR

Joe Subich, W4TV wrote:

Don Wilhelm-4

Re: K3 DSP AGC Question

Dave,

I believe you are asking for a more "rounded knee" on the AGC attack
curve. I don't know if that is feasible without a lot of work on Lyle's
part - he would have to answer. Right now, (as you noticed) the slope
of the AGC line between the threshold point and the point where the
hardware AGC kicks in is almost linear. I am not certain how much more
computation would be required to produce a more rounded knee, nor how
fast the DSP engine can compute a more complex function - if there is
not adequate engine speed, things could become quite distorted.

Changing that function should not change the threshold levels - the
point where the knee occurs just depends on the threshold, and the shape
of the knee should not influence it. In use, a softer knee may make the
use of a lower threshold more practical.

73,
Don W3FPR

Dave - AB7E wrote:
> I also think that the current max AGC threshold is too low, but I have another question. Why is it necessary for the K3 AGC to have such a sharp elbow at the point where the AGC kicks in? The Clifton Labs plots show such a sharp bend that it seems multi-signal in-band intermod is inevitable, especially with higher SLP settings. Wouldn't it be feasible, and more desirable, to have some more gradual inflection point? I would think that something like a parabolic shape would be better, and the DSP AGC is just the implementation of an algorithm, correct? I suppose that would tend to blur the distinction between different THR settings, but so what?
>
>
______________________________________________________________
Elecraft mailing list
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Post: mailto:[hidden email]

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Guy, K2AV

Re: K3 DSP AGC Question

In reply to this post by David Gilbert

Traversing the knee does not cause distortion, because the first
transition around the knee is *** HELD *** and only released many,
many cycles later even at the fastest possible FAST AGC, and only
released if the level has subsided.

This is not at all the same thing as having an amplifier device curve
of that shape and subjecting every single audio cycle to such an
amplification curve which would create tons of distortion.

What can happen at a much slower rate (below audio frequencies so
technically not causing distortion), is that the very fastest AGC,
with its quick release, combined with an ambient noise amplified (by
inappropriate PRE/ATT/RFGAIN settings) above the AGC threshold, will
effectively push down every signal to the noise level, presenting to
the ear what sounds like all signals are at the noise level.

In a crowded room our brain neatly interprets stereophonic sound to
separate out a single spatially diverse conversation from dozens of
others at essentially the same level. In research using a monophonic
recording of the multiple conversations from a single microphone in
the same room, very few can discern individual conversations, and most
find any length of listening to the recording irritating and tiring.

The monophonic muddle created by self-defeating PRE/ATT/RFGAIN/AGC
combinations is probably worse than the monophonic room recording, as
we are intending to sit there for a while, like for a whole contest.
At some point the stressed-out brain is emotionally looking for a
scapegoat, and will fasten on the closest object.

Those of us who had Klingon pain-stick training doing traffic nets in
80 meter summer QRN can will ourselves through silly control setting
combinations without learning how to use them. The rest of us will
need to learn how to use them, or go buy a box that decides all our
choices for us.

I decidely prefer to keep the choices. Despite all claims to
contrary, PRE/ATT/RFGAIN/AGC is not rocket science.

73, Guy.

On Wed, Feb 10, 2010 at 1:38 AM, Dave - AB7E <[hidden email]> wrote:

>
>
> I also think that the current max AGC threshold is too low, but I have another question. Why is it necessary for the K3 AGC to have such a sharp elbow at the point where the AGC kicks in? The Clifton Labs plots show such a sharp bend that it seems multi-signal in-band intermod is inevitable, especially with higher SLP settings. Wouldn't it be feasible, and more desirable, to have some more gradual inflection point? I would think that something like a parabolic shape would be better, and the DSP AGC is just the implementation of an algorithm, correct? I suppose that would tend to blur the distinction between different THR settings, but so what?
>
> Maybe somebody can educate me ...
>
> 73,
> Dave AB7E
>
>
>
>
> ------Original Mail------
> From: "Don Wilhelm" <[hidden email]>
> To: "Joe Subich, W4TV" <[hidden email]>,
> <[hidden email]>
> Sent: Wed, 10 Feb 2010 01:06:09 -0500
> Subject: Re: [Elecraft] K3 DSP AGC Question
>
> Joe,
>
> Can you elaborate your reasons for this suggestion. I had come to
> believe that the best situation is to place attenuation before the first
> mixer to give the greatest amount of dynamic range (headroom).
>
> Yes, I agree that the AGC Threshold could be raised in the K3 and would
> be beneficial. I have felt the default of 005 was too low.
>
> 73,
> Don W3FPR
>
> Joe Subich, W4TV wrote:
>> Perhaps one should get the ambient well down in the ADC operating
>> range but killing gain (adding loss) before the first mixer and
>> the roofing filter is not the way to do it. If you want to
>> better align the dynamic range of the receiver (or specifically
>> the ADC) to conditions, the attenuation should come in the
>> IF - preferably divided between the first IF and 2nd IF.
>>
>> However, there would still be no apparent reason that the K3
>> should not be capable of sustaining an AGC threshold at least
>> 10 db higher than currently set with AGC THR = 008 whether
>> that be reached with preamp on, preamp off or attenuator on.
>>
>> 73,
>>
>> ... Joe, W4TV
>>
>>
>
> ______________________________________________________________
> 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
>

David Gilbert

Re: K3 DSP AGC Question

In reply to this post by KK7P

Guy,

That's a terrific explanation ... thanks!

I had thought, however, that AGC DCY = SOFT was added to the menu several months ago because the AGC actually was capable of "bouncing" in response to signals ... even individual elements of CW. If so, that would still imply that a more rounded curve might be beneficial.

73,
Dave AB7E

------Original Mail------
From: "Guy Olinger K2AV" <[hidden email]>
To: "Dave - AB7E" <[hidden email]>,
<[hidden email]>,
<[hidden email]>,
<[hidden email]>
Sent: Wed, 10 Feb 2010 08:58:00 -0500
Subject: Re: [Elecraft] K3 DSP AGC Question

Traversing the knee does not cause distortion, because the first
transition around the knee is *** HELD *** and only released many,
many cycles later even at the fastest possible FAST AGC, and only
released if the level has subsided.

This is not at all the same thing as having an amplifier device curve
of that shape and subjecting every single audio cycle to such an
amplification curve which would create tons of distortion.

What can happen at a much slower rate (below audio frequencies so
technically not causing distortion), is that the very fastest AGC,
with its quick release, combined with an ambient noise amplified (by
inappropriate PRE/ATT/RFGAIN settings) above the AGC threshold, will
effectively push down every signal to the noise level, presenting to
the ear what sounds like all signals are at the noise level.

In a crowded room our brain neatly interprets stereophonic sound to
separate out a single spatially diverse conversation from dozens of
others at essentially the same level. In research using a monophonic
recording of the multiple conversations from a single microphone in
the same room, very few can discern individual conversations, and most
find any length of listening to the recording irritating and tiring.

The monophonic muddle created by self-defeating PRE/ATT/RFGAIN/AGC
combinations is probably worse than the monophonic room recording, as
we are intending to sit there for a while, like for a whole contest.
At some point the stressed-out brain is emotionally looking for a
scapegoat, and will fasten on the closest object.

Those of us who had Klingon pain-stick training doing traffic nets in
80 meter summer QRN can will ourselves through silly control setting
combinations without learning how to use them. The rest of us will
need to learn how to use them, or go buy a box that decides all our
choices for us.

I decidely prefer to keep the choices. Despite all claims to
contrary, PRE/ATT/RFGAIN/AGC is not rocket science.

73, Guy.

On Wed, Feb 10, 2010 at 1:38 AM, Dave - AB7E <[hidden email]> wrote:

12345