[Elecraft] K3 AGC dead spot

[Guy Olinger K2AV]

The thing to note here, this ain't your daddy's analog radio, the only
actual "stage gain" adjustments you have are ATT and PRE.  The rest is
all in the numbers, as the front panel knobs are just numerical advice
to the firmware.  They don't directly control anything.

What needs to happen is a calibration of what voltage sent to the
variable 8 MHz stage produces a specific number out of the 15 kHz
analog-to-digital converter, etc, and exactly what stage gain change
occurs when PRE enabled, ATT enabled.

Also note here that the PRE and ATT button is also just advice to the
firmware.  The button does not directly control a circuit, as opposed
to a DPDT switch carrying RF on its terminals that literally removes a
PRE from the circuit.  The in and out is done by a one or zero bit
state from the MCU, converted to a switching voltage which biases
various diodes which change the signal path in the RX.

All of this stuff gets tabled up in the firmware, which constantly
consults it to set levels in the output and optimize IF gain into the
15 kHz ADC.  If the numbers in the table are goofy, so will the
behavior be goofy.

Better to calibrate the K3 on a signal source (over the years, the
XG-2 will pay for itself, over and over) and have it right.

If you bought the radio assembled, this was done for you when you got
it.  If you assembled it, needs doing.

Personally, sometimes I think the tables get hosed by ??? and needs
redoing. Done it a couple of times to restore normal function and have
no clue what happened to make it that way.

73, Guy.

On Thu, Oct 21, 2010 at 6:41 AM, Mike <nf4l at nf4l.com> wrote:
>
> Thanks, Vic.
>
> Per Dale's suggestion I did a calibration using factory defaults, and the dead spot
> is gone, and the S-meter is back to rising with a decrease of RF gain. Dagnab it.....
>
> 73, Mike NF4L
>
> On 10/20/2010 11:50 PM, Vic K2VCO wrote:
>> My guess is that you need to do the RF Gain Calibration procedure with the K3 utility. If
>> you have an XG1 or XG2 you can use it as a calibrated source, or if not you can tell the
>> utility to use the factory default settings.
>>
>> On 10/20/2010 8:13 PM, Mike wrote:
>>> Tonight I noticed that from about 2:00 to 2:30 on the RF gain encoder, the receiver
>>> goes dead. It's not dependent on the THR or SLP settings which I adjusted to match
>>> some advice given here short time past.
>>>
>>> I also realized my S-meter doesn't rise as the RF gain is reduced. I like that, but I
>>> don't know how it got that way. :-P
>>>
>>> I have the latest firmware.
>>>
>>> It's not really a big deal, but is is puzzling.
>>>
>>> 73, Mike NF4L
>
>
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