[Elecraft] K3 AGC dead spot

[Mike]

I understand that the knob labeled RF doesn't really control RF gain, but since 
Elecraft labeled it that way, I think it's better to reference it that way.

I have an XG2, and had done the RF gain calibration using it. Dale recommended doing 
it using the factory defaults. I'm waiting to hear back from him why.

It's a kit, just a tad over a year old, with all available mods.

The mechanism by which the tables may get hosed is the same principle which makes 
them work. HPFM. (HocusPocusFreakyMagic) :-D .

73, Mike NF4L

On 10/21/2010 7:42 AM, Guy Olinger K2AV wrote:
> 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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