K3 RX AGC right after a transmission

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K3 RX AGC right after a transmission

Arie Kleingeld PA3A-2
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During the CQWW CW we found that RIGHT AFTER a transmission the RX AGC was STILL busy doing its job and getting back to a lower level (s-meter dropping from about s9 to the band noise level)
(AGC was at slow).
 
We SUSPECT that the AGC was still at the level from BEFORE the transmission. So working a strong station gives a problem if the next one is weak, you'll miss the first letters of the call. We're not sure about the cause but we encoutered this problem quite often.
It would be better that after a transmission the RX would start at band noise level and that there is no legacy whatsoever.
 
Anyway, the work around was setting the AGC to fast.
 
 
Did anyone else experience this? Is this a known problem?
 
Setting agc: threshold 5, the AGC ramp-up at 12, the fall-off setting at default value (20)
SW: latest Beta.
K3 # 1255
 
 
 
73
Arie PA3A

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Re: K3 RX AGC right after a transmission

KK7P
Hello Arie!

> ... We SUSPECT that the AGC was still at the level from
> BEFORE the transmission.

Yes, AGC is suspended during transmission, then resumes during receive.
  The assumption is that the band hasn't changed that much in the
milliseconds (CW QSK) to several seconds (SSB voice).

> ...the work around was setting the AGC to fast.

In general, fast AGC is most often used for CW< and slow AGC for voice
or data operation.

73,

Lyle KK7P
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Re: K3 RX AGC right after a transmission

dj7mgq
Hi Lyle,

> Yes, AGC is suspended during transmission, then resumes during receive.
>  The assumption is that the band hasn't changed that much in the
> milliseconds (CW QSK) to several seconds (SSB voice).

I've noticed this in SSB contests - I'm not sure if we exchanged mails
because of this or not.

The effect sounded as if the K3 had become "hard of hearing" and took a
second or so to recover. What I am no longer sure about, is whether I
had set AGC to slow or fast.

While the assumption that during transmission reception levels have not
changed, generally tends to be correct, at times it is not. I wonder if
it would be too complex to return from transmission in an AGC "fast"
mode and then switch to the mode which the user has chosen after say
100mS or so. I could imagine that with a bit of tweaking, an automatic
change of the AGC timing shouldn't be noticeable except for the fact
that the "recovery" after transmission would be "masked".

Just an idea...

vy 73 de toby
--
DD5FZ (ex 4n6fz, dj7mgq, dg5mgq, dd5fz)
K2 #885, K2/100 #3248, K3/100 #67




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Re: K3 RX AGC right after a transmission

ab2tc
Hi,

I have this problem also and I have reported it before. It is *very* annoying when you are trying to get through a pileup. My AGC is in the slow mode. I am sure it would be no problem if it were set to fast. All we are asking for is for the AGC be reset to a no-signal condition when resuming reception after a transmission. I am sure that would solve the problem completely.


Toby Deinhardt wrote
Hi Lyle,

> Yes, AGC is suspended during transmission, then resumes during receive.
>  The assumption is that the band hasn't changed that much in the
> milliseconds (CW QSK) to several seconds (SSB voice).

I've noticed this in SSB contests - I'm not sure if we exchanged mails
because of this or not.

The effect sounded as if the K3 had become "hard of hearing" and took a
second or so to recover. What I am no longer sure about, is whether I
had set AGC to slow or fast.

<snip>
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Re: K3 RX AGC right after a transmission

K8AC
In reply to this post by KK7P
Lyle - I too noticed this during the contest and at times it was a real pain.  Switching to fast AGC circumvented it, but there are many reasons that I prefer to run slow AGC.  Also, many of us do NOT run full break-in for a variety of good reasons.  In that case, having the AGC state resume where it was at the last receive point - perhaps 3-6 seconds ago - isn't very useful.  In many cases, the last AGC state was set by a strong station and the new receive state starts with a very weak signal calling.

I don't ever recall running into this situation on my K2 or Pro III and really would prefer some sort of option to prevent it from happening on the K3.  Perhaps we don't need a new option, but could key an operational change from whether or not QSK was being used?  


Lyle Johnson wrote
Hello Arie!

> ... We SUSPECT that the AGC was still at the level from
> BEFORE the transmission.

Yes, AGC is suspended during transmission, then resumes during receive.
  The assumption is that the band hasn't changed that much in the
milliseconds (CW QSK) to several seconds (SSB voice).

> ...the work around was setting the AGC to fast.

In general, fast AGC is most often used for CW< and slow AGC for voice
or data operation.

73,

Lyle KK7P
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Re: K3 RX AGC right after a transmission

Bill W4ZV
In reply to this post by ab2tc

ab2tc wrote
Hi,

I have this problem also and I have reported it before. It is *very* annoying when you are trying to get through a pileup. My AGC is in the slow mode. I am sure it would be no problem if it were set to fast. All we are asking for is for the AGC be reset to a no-signal condition when resuming reception after a transmission. I am sure that would solve the problem completely.
I believe you're asking the AGC to do something it cannot do.  I never use Slow AGC, even on SSB.  The one situation I might is if I were ragchewing on SSB.  Otherwise you'll have problems with rapid QSB or with strong stations on top of a weak DX signal in a pileup.  There's simply NO way Slow AGC can handle those situations...period.  I even found it necessary to turn my AGC off in the contest this weekend when we had strong lightning crashes and I was trying to copy noise floor JAs on 160.  Even Fast AGC (set to the 200 dB/s maximum) could not handle that situation.

73,  Bill
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Re: K3 RX AGC right after a transmission

ab2tc
Hi,

I am fully aware that slow AGC has its limitations in the presence of static crashes, although the K3 does a fairly good job of not "hanging" on those. All I and others are asking is that the receiver not remember the signal strength prior to transmitting, but rather reset it to a no-signal condition when resuming receive. This is not asking the impossible.


Bill W4ZV wrote
I believe you're asking the AGC to do something it cannot do.  I never use Slow AGC, even on SSB.  The one situation I might is if I were ragchewing on SSB.  Otherwise you'll have problems with rapid QSB or with strong stations on top of a weak DX signal in a pileup.  There's simply NO way Slow AGC can handle those situations...period.  I even found it necessary to turn my AGC off in the contest this weekend when we had strong lightning crashes and I was trying to copy noise floor JAs on 160.  Even Fast AGC (set to the 200 dB/s maximum) could not handle that situation.

73,  Bill
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Re: K3 RX AGC right after a transmission

Barry N1EU

ab2tc wrote
I am fully aware that slow AGC has its limitations in the presence of static crashes, although the K3 does a fairly good job of not "hanging" on those. All I and others are asking is that the receiver not remember the signal strength prior to transmitting, but rather reset it to a no-signal condition when resuming receive.
But if there's a strong signal on frequency, don't you risk blasting your eardrums?  

(not sure there's a problem with the way it is . . .)

73,
Barry N1EU
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Re: K3 RX AGC right after a transmission

Bill W4ZV
In reply to this post by ab2tc

ab2tc wrote
I am fully aware that slow AGC has its limitations in the presence of static crashes
...and rapid QSB
...and very strong signals on top of weak ones (i.e. DX pileups)

Other than that, slow AGC works fine!  But if you no QRN bursts, no QSB and no large variations in signal strengths, then you probably don't even need AGC.

73,  Bill

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Re: K3 RX AGC right after a transmission

P.B. Christensen
In reply to this post by ab2tc
> I am fully aware that slow AGC has its limitations in the presence of
> static
> crashes, although the K3 does a fairly good job of not "hanging" on those.
> All I and others are asking is that the receiver not remember the signal
> strength prior to transmitting, but rather reset it to a no-signal
> condition
> when resuming receive.

So that we can be subject to the full AGC gain (the no-signal condx) between
T/R transmissions in the presence of strong signals?  Even with ample fast
attack time, that does not seem like a pleasant listening experience.

Paul, W9AC

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Re: K3 RX AGC right after a transmission

Geoffrey Mackenzie-Kennedy
In reply to this post by Barry N1EU
Barry N1EU wrote:

> ab2tc wrote:
>>
>> I am fully aware that slow AGC has its limitations in the presence of
>> static crashes, although the K3 does a fairly good job of not "hanging"
>> on
>> those. All I and others are asking is that the receiver not remember the
>> signal strength prior to transmitting, but rather reset it to a no-signal
>> condition when resuming receive.
>>
>
> But if there's a strong signal on frequency, don't you risk blasting your
> eardrums?
>
> (not sure there's a problem with the way it is . . .)
>
> 73,
> Barry N1EU

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

True, but one method to help protect your eardrums if there is a strong
signal on frequency, and while the AGC is catching up after being reset, is
to slice / clip the audio at a level above the normal listening level peaks
but safely below the "blast threshold". Not a pretty solution but at least
it is not too complicated.

73,
Geoff
GM4ESD

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RE: K3 RX AGC right after a transmission

Arie Kleingeld PA3A-2
In reply to this post by KK7P
Lyle,

Thank you for your prompt response.



Slow agc or fast agc or CW is not the point. The problem holds for SSB
contesting as well.
Nor is it about band conditions.

It IS about working a S4 station in a contest after a S9+20 station. QSO
responses are quick and so is going from one QSO to another. I missed
the first letters of a weak station several beacause of too slow agc,
and had to ask for a repeat.


All I ask is that the AGC backs off and starts all over again when going
to receive after a transmission.
With all that DSP stuff that must be possible. I have confidence that,
after implementing this, the K3 will not bang my ears every time. You'll
find a way to avoid that.
Maybe the solution is in a temporary fast response of the AGC so that
the AGC can drop down to a low S3 level in 100 ms or so, and then engage
the AGC setting again as set by the operator.  This could be analog
thinking so there probably is a more clever and simple way in DSP.

As for modifications to the K3 SW, I think that (in my opinion....
sorry) this is a more important issue that a beeping response when I
press a button on the K3.


73
Arie PA3A



-----Oorspronkelijk bericht-----
Van: Lyle Johnson [mailto:[hidden email]]
Verzonden: maandag 1 december 2008 3:15
Aan: Arie Kleingeld PA3A
CC: [hidden email]; [hidden email]; 'Ad van Ginneken'
Onderwerp: Re: [Elecraft] K3 RX AGC right after a transmission


Hello Arie!

> ... We SUSPECT that the AGC was still at the level from BEFORE the
> transmission.

Yes, AGC is suspended during transmission, then resumes during receive.
  The assumption is that the band hasn't changed that much in the
milliseconds (CW QSK) to several seconds (SSB voice).

> ...the work around was setting the AGC to fast.

In general, fast AGC is most often used for CW< and slow AGC for voice
or data operation.

73,

Lyle KK7P


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