[Elecraft] K3 / RF gain - S meter issue - Similar issue

[Wes Stewart]

Personally, I wouldn't go so far as to say the radio performs correctly. Without 
writing a long history, let's just say that I discovered this RF gain issue 8 or 
9 years ago.  I demonstrated it to an Elecraft engineer in my shack who had 
brought along his fully up to date K3 which we compared.  They were widely 
different.  Subsequently, I did a lot of beta testing of firmware that I believe 
spawned the RF gain calibration program.

In my opinion based on inspection of the schematic, the issue resides in the fet 
post-filter amplifier that is controlled by the "hardware" AGC (and manual "RF" 
gain control)  The specs on this device are very loose, IIRC, Gm can vary 2:1.  
Thus the response of this fet to AGC/RF gain varies from radio to radio, and as 
seen in another post, between the main RX and second RX in the same radio.  As I 
understand it, and I would love for someone at Elecraft to correct me if I'm 
wrong, the RF gain calibration program measures the radio gain control 
characteristics and generates a lookup table of correction factors to apply to 
linearize the control.

If I'm correct, I always been troubled by questions about the speed of this 
process.  Being an analog guy I understand resistor-diode networks used for 
similar purposes that operate essentially instantaneously.   The digital process 
not so much.

Wes  N7WS



On 12/14/2017 9:16 AM, Dan Atchison via Elecraft wrote:
> I have a similar - but different! - issue on one of my Elecraft's.
>
> I own both a K3 and a K3s.  Both are configured equally with the K3 having 
> been upgraded to the highest level to achieve near K3s equivalency.
>
> My K3s RF Gain control works exactly as expected, i.e. as the control is 
> rotated counter-clockwise the "S-Meter" increases to a point at almost full 
> scale.
>
> On the K3, however, as the RF Gain control is rotated counter-clockwise and 
> the "S-Meter" increases to about the "40-over" point at the control's 10 
> o'clock position the "S-Meter" then inexplicably drops to the "S9" position 
> where it remains for the remainder of the RF gain control counter-clockwise 
> rotation. This shouldn't be but like N1LN's issue, the radio does otherwise 
> perform correctly.  I have done everything that N1LN has done including the RF 
> Gain calibration using a signal generator.
>
> Very strange, indeed.
>
> Dan -- N3ND
>
> *************************************
>
> Date: Wed, 13 Dec 2017 16:25:20 -0500
> From: "Bruce Meier"<bemeier at bellsouth.net>
> To:<elecraft at mailman.qth.net>
> Subject: [Elecraft] K3 / RF gain - S meter issue
>
>
> Looking for suggestions here from someone that might have experienced this
> same issue - -
>
>
>
> I have (2) K3 units (not the S model) that are acting different when the RF
> gain adjustments are turned fully counter clockwise.
>
> ?  Unit one ? s/n 1062: When the RF gain is decreased to full counter
> clockwise position the S-Meter registers full scale (60db over S9) as
> expected.
>
> ?  Unit two ? s/n 1193:  When the RF gain is decreased to full counter
> clockwise position the S-Meter registers only S8.
>
>  Facts:
>
> ?  With the exception of the S-Meter readings with RF gain settings, both
> units are working fine
>
> ?  Both units have ?almost? all mods installed.  If not all, they are at
> least both the same.
>
> ?  Both units are running the same version of microcode (5.54) (2.88) (2.88)
> (1.26)
>
> ?  Both units seem to register very close actual RF gain of stations when
> connected when tested on the same antenna
>
> ?  Both units have the new synthesizers.
>
> ?  Both units have second RX
>
> ?  In both cases (both units) I can hear the audio level decreasing linearly
> as expected as the RF gain is turned counter clockwise
>
> I have tried to initialize the K3 and reload the firmware resulting in no
> change to the RF gain / S-Meter readings.
>
>
>
> Elecraft Tech Support suggested:
>
> ?  Calibrating the s-meter ? did nothing
>
> ?  Next suggestion ? send the rig to California.
>
>
>
> Anyone have this issue and fixed it??
>
>
>
> 73,
>
> Bruce N1LN
>
>
>
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