[K2] Setting the AGC Threshold Section of Build

[Don Singer]

I am finishing the first phase of my K2 build, and everything has gone
well up to this point. All resistance and voltage tests are fine.

When I went to set the AGC Threshold as per page 47 of the K2 Manual, I
got 5.0 volts as the lowest setting I could achieve when adjusting R1 on
the Control Board , so I followed the instructions at the top of page 48
and followed the AGC Level Application Note and installed the 15K
resistor between pins 3 and 4 of RP6 on the Control Board.

The resistance across the 15k resistor, once installed on the Control
Board on pins 3 and 4, was 3K. I reflowed the solder to see if I could
get the 3.5k ohms specified on the worksheet, but still got 3K and
thought that is good enough.

I reassembled the K2 and ran the AGC Threshold section again - but,
instead of being closer to 3.8 volts, I am now at 6.2 volts as the
lowest reading I could get. The lowest voltage went up and not down? Why
is that?

I am not sure if this is meaningful or not so I am holding from moving
forward until I know if this is an issue, or just move on, or remove the
15k resistor across pins 3 and 4 of RP6?

Thanks,
Don KF7DS
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[Don Wilhelm-4]

Don. measure the voltage at the output side of Control Board 4.  It
should be in the vicinity  of 8 volts.

I would suggest removing the 15k resistor and checking the voltage at CB
U2 pin 5.  If that voltage is 3.7 volts or more, that will work out just
fine.  If lower than 3.7 volts, add back the resistor and set he AGC
Threshold voltage for somewhere between 3.75 amd 3.8 volts as measured
at Control Board U2 pin 5.

73,
Don W3FPR

On 8/24/2012 8:39 PM, Don Singer wrote:

> I am finishing the first phase of my K2 build, and everything has gone
> well up to this point. All resistance and voltage tests are fine.
>
> When I went to set the AGC Threshold as per page 47 of the K2 Manual, I
> got 5.0 volts as the lowest setting I could achieve when adjusting R1 on
> the Control Board , so I followed the instructions at the top of page 48
> and followed the AGC Level Application Note and installed the 15K
> resistor between pins 3 and 4 of RP6 on the Control Board.
>
> The resistance across the 15k resistor, once installed on the Control
> Board on pins 3 and 4, was 3K. I reflowed the solder to see if I could
> get the 3.5k ohms specified on the worksheet, but still got 3K and
> thought that is good enough.
>
> I reassembled the K2 and ran the AGC Threshold section again - but,
> instead of being closer to 3.8 volts, I am now at 6.2 volts as the
> lowest reading I could get. The lowest voltage went up and not down? Why
> is that?
>
> I am not sure if this is meaningful or not so I am holding from moving
> forward until I know if this is an issue, or just move on, or remove the
> 15k resistor across pins 3 and 4 of RP6?
>
> Thanks,
> Don KF7DS
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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[Don Singer]

Thanks Don. CB checked out at 7.85v and removed resistor. Current drain test was good at .14a

Best Don KF7DS

Don Wilhelm <[hidden email]> wrote:

>Don. measure the voltage at the output side of Control Board 4.  It
>should be in the vicinity  of 8 volts.
>
>I would suggest removing the 15k resistor and checking the voltage at CB
>U2 pin 5.  If that voltage is 3.7 volts or more, that will work out just
>fine.  If lower than 3.7 volts, add back the resistor and set he AGC
>Threshold voltage for somewhere between 3.75 amd 3.8 volts as measured
>at Control Board U2 pin 5.
>
>73,
>Don W3FPR
>
>On 8/24/2012 8:39 PM, Don Singer wrote:
>> I am finishing the first phase of my K2 build, and everything has gone
>> well up to this point. All resistance and voltage tests are fine.
>>
>> When I went to set the AGC Threshold as per page 47 of the K2 Manual, I
>> got 5.0 volts as the lowest setting I could achieve when adjusting R1 on
>> the Control Board , so I followed the instructions at the top of page 48
>> and followed the AGC Level Application Note and installed the 15K
>> resistor between pins 3 and 4 of RP6 on the Control Board.
>>
>> The resistance across the 15k resistor, once installed on the Control
>> Board on pins 3 and 4, was 3K. I reflowed the solder to see if I could
>> get the 3.5k ohms specified on the worksheet, but still got 3K and
>> thought that is good enough.
>>
>> I reassembled the K2 and ran the AGC Threshold section again - but,
>> instead of being closer to 3.8 volts, I am now at 6.2 volts as the
>> lowest reading I could get. The lowest voltage went up and not down? Why
>> is that?
>>
>> I am not sure if this is meaningful or not so I am holding from moving
>> forward until I know if this is an issue, or just move on, or remove the
>> 15k resistor across pins 3 and 4 of RP6?
>>
>> Thanks,
>> Don KF7DS
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>

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