[Elecraft] K3 Receiver mush

[Joe Subich, W4TV]

The hardware AGC engages at about -45 (S9 + 20 dB).  That is most
certainly the final flattening you are seeing in the transfer
characteristic.

Otherwise the slope for each slp setting will generate roughly parallel
transfer curves from the threshold point (witness the parallel curves
for all of the SLP 15 cases as well as for Thr 8, SLP 7 and THR 15,
SLP 7).  K8ZOA produced similar curves showing parallel behavior with
SLP held constant as the threshold is changed.  See:
   <http://www.cliftonlaboratories.com/elecraft_k3_agc_and_s-meter.htm>

Jack also derived charts showing the change in output (audio) level
per 10 dB of input (RF) level for each value of slope (SLP) and the
signal level for  AGC Threshold (THR).  That information can be found
in the same article.  Unfortunately, Jack's data is from very early
firmware and was not repeated after the firmware was never updated to
include values for THR greater than 8.

73,

    ... Joe, W4TV


On 2/23/2017 2:58 PM, Cady, Fred wrote:
> http://www.ke7x.com/home/miscellaneous-k3-information/agc-4-51
>
>
> The transfer characteristic is pretty linear from an input signal of nearly -120 dBm to about -45 dBm with AGC off.  Signals above that are being clipped by some other non-linear process, probably the hardware AGC.    I don't remember if I had the AF LIM on when I took these data.
>
> Cheers,
>
> Fred KE7X
>
>
>
> ________________________________
> From: Elecraft <elecraft-bounces at mailman.qth.net> on behalf of W0MU Mike Fatchett <w0mu at w0mu.com>
> Sent: Thursday, February 23, 2017 9:08 AM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 Receiver mush
>
> What happens when you turn the AGC off and ride the rf gain?  Do these
> setting still have some effect or should they be set up differently?
>
> I assume when you use 12/8/soft most people are using AGC-F?
>
>
> On 2/22/2017 1:54 PM, Irma Linas wrote:
>> Hi everybody,
>>
>> Following the advice in one of the posts here, I have changed the AGC
>> settings on my K3+ ( new sync and IO boards as per Elecraft mods kit
>> turning the old K3 actually into K3S). I've put the AGC THR to 12, AGS SLP
>> to 8, AGC DCY to SOFT in the Config menu.
>> Whaw! The efffect was immediate ,very obvious and pleasant! The strong
>> signals were strong, the weak were weak , but there was no pile-up mush!
>> What was especially of great importance for me - the long time annoying
>> problem of receiver hiss and humm when receiving on narrow band 250 Hz
>> filter was gone! Before, when switching the narrow filter on on weak
>> signals on the noisy band the signal actually was totally covered by the
>> increased noise in the filter. I think now it was due to the AGC reacting
>> to the noise and amplifying it in the narrow band mode because of the too
>> low AGC THR setting. When the threashhold was increased, the AGC stopped
>> equalizing the noise and only work on the signal. The result was awsome!
>> You switch the 250 hz roofing filter on and all the noise and interfering
>> stns are gone, and the signal you want is there! It could be a very loud
>> one or a weak one , but it is there and the noise is not!
>> I recommend everybody to try out this and experiment with the AGC settings
>> on your K3 radios!
>> 73 de Linas LY2H
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