[Elecraft] APF and audio limiting

[Joe Subich, W4TV]

>> Remember, the AGC is only supposed to bring things to the level of
 >> your AF output setting.

No. AGC should never "bring up" the level.  AGC *REDUCES* the level of
signals above the AGC threshold.  One normally sets the audio level for
signals *at the AGC threshold* or below and AGC keeps stronger signals
from exceeding that level (by the amount of the "slope" if one is not
using a "hard" threshold).

The difference with an *AUDIO PEAK FILTER* is that the APF is in the
AUDIO circuit *AFTER* the detector and *OUTSIDE* the AGC loop.  Since
the PEAK gain of the K3 APF is roughly 10 dB - see the response here:
http://n1eu.com/K3/K3_apf.htm - this can cause an issue with strong
signal but is a big advantage with signals at or near the noise level
(and below the AGC threshold).  Of course, the gain is exactly why APF
can be turned on and off ... you don't want it on with strong signals -
only with those at the noise signals where it makes a difference!

73,

    ... Joe, W4TV


On 11/6/2010 8:20 PM, The Smiths wrote:
>
> I think that your understanding of the AGC is probably pretty good.  I also think that most people don't know how to set their AGC properly.  Yes, there should have been SOME control over the loudness of the other signal, but because the Peak filter brings everything up as it does it can also take an S9 signal and make it sound like an S40 over signal too, even when the AGC is compressing things..
>
> Remember, the AGC is only supposed to bring things to the level of your AF output setting.  Therefore if you have your AF all the way up, well, that's as loud as the AGC will put it under Sloping conditions.. It doesn't mean that EVERY weak signal will also be within your AGC Threshold. What "sounds loud" because of the APF is on doesn't mean that it's opening your threshold control in the AGC.  There in lies your problem I think.. What you thought was under AGC control, really wasn't!. What you were actually hearing is proper Dynamic range you should have.  So the volume control still comes into play.
>
> I'll send you a copy of my AGC tutorial offline.  I hope this helps you out some.
>
>
>> Date: Sat, 6 Nov 2010 19:46:11 -0400
>> From: nf4l at nf4l.com
>> To: elecraft at mailman.qth.net
>> Subject: Re: [Elecraft] APF and audio limiting
>>
>> Thanks Tom.
>>
>> Well, I kinda thought it shouldn't blast my ears that hard. Audio *WASN'T* up too
>> loud for the signal I was after. Maybe I don't understand what AGC does. That's why I
>> asked the questions I did.
>>
>> On 11/6/2010 6:21 PM, Amateur Radio Operator N5GE wrote:
>>> On Sat, 06 Nov 2010 18:04:18 -0400, Mike<nf4l at nf4l.com>  wrote:
>>>
>>> Sounds normal to me.
>>>
>>> Audio up too loud and APF on, then a strong signal transmits on the frequency
>>> you are listening to....
>>>
>>> What do you think it SHOULD have done? You didn't say.
>>>
>>> Tom
>>> Radio Amateur N5GE
>>>
>>>> On 11/4/2010 9:48 PM, Mike wrote:
>>>>> I'm playing with the new APF, and trying to get a REALLY weak QSO to pop. I have the
>>>>> volume cranked up pretty good, and a REALLY strong station throws in their call. I
>>>>> thought my speakers had blown. Glad I wasn't wearing cans.
>>>>>
>>>>> My CONFIG:AF is 18, AGC = F.
>>>>>
>>>>> Was I doing something wrong? Anybody else experience this? Do we need/can we have
>>>>> better audio limiting?
>>>>>
>>>>> 73, Mike NF4L
>>>
>>
>>
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