Problem setting AGV Threshhold

[Matthew Denson]

Hi All,

I am building my K2 and have reached the initial checkout steps before building the receiver.

On page 48 of my manual (Rev G if that matters) the instructions say to "Adjust R1 for a reading of 3.80...."

On my K2 the way it is right now the range of voltages I get by changing R1 is 2.1-3.28Vdc.  Hmmm?

I looked at the schematic on the way to work today (I'm still there) and it doesn't look like there are that many variables here.  It is a simple voltage divider of the 8v regulated voltage to ground as far as I can see and it seems like the max voltage should be 1/2 of 8V when R1 is completely shorted out.  I haven't checked the 8V source cause I haven't been back home.  

Maybe extra useless info - I don't know how the internal volt meter works but it is reading out correctly (that is I get the same reading as my DMM where I have made identical measurements) so I assume that the 5V regulator is working right.

Any thoughts on which points to check?  Is my reading of the schematic too simplistic?

73,
Matthew




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[Don Wilhelm-3]

Matthew,

You reading of the schematic is correct - the voltage at U2 pin 5 is the
result of a voltage divider network - nothing less, nothing more.  If
you have a problem here, one or more of the resistors involved is wrong,
or the voltage from the 8 volt regulator is not correct.

The RF Gain control is one of those resistors, so be certain it is set
to the full clockwise position.

73,
Don W3FPR

Matthew Denson wrote:

> Hi All,
>
> I am building my K2 and have reached the initial checkout steps before building the receiver.
>
> On page 48 of my manual (Rev G if that matters) the instructions say to "Adjust R1 for a reading of 3.80...."
>
> On my K2 the way it is right now the range of voltages I get by changing R1 is 2.1-3.28Vdc.  Hmmm?
>
> I looked at the schematic on the way to work today (I'm still there) and it doesn't look like there are that many variables here.  It is a simple voltage divider of the 8v regulated voltage to ground as far as I can see and it seems like the max voltage should be 1/2 of 8V when R1 is completely shorted out.  I haven't checked the 8V source cause I haven't been back home.  
>
> Maybe extra useless info - I don't know how the internal volt meter works but it is reading out correctly (that is I get the same reading as my DMM where I have made identical measurements) so I assume that the 5V regulator is working right.
>
> Any thoughts on which points to check?  Is my reading of the schematic too simplistic?
>

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[Matthew Denson]

Hi All,

Thanks for the pointer Don.

I looked last night and found (blush) that I was checking the voltage at the wrong pin.  I'm glad I took a step back and came at it fresh without pulling my hair out. Fortunately that is a trait I've learned from programming as a job.

So, when measuring the right pin, the max voltage I can get is 3.77v.  The voltage at the 8v regulator output is 7.79v and at the regulator input has been in the range of 12.9-13.3v depending on the battery's charge.  I may be within the range of error for my DMM, but I don't know.  

Is the voltage out of the regulator within the expected tolerance?
Is it a problem that I have maxed out the trimmer pot to get 3.7v or is that expected?

Thanks for your help.

73, Matthew

----- Original Message ----
From: Don Wilhelm <[hidden email]>
To: Matthew Denson <[hidden email]>
Cc: [hidden email]
Sent: Monday, July 30, 2007 4:07:26 PM
Subject: Re: [Elecraft] Problem setting AGV Threshhold

Matthew,

You reading of the schematic is correct - the voltage at U2 pin 5 is the
result of a voltage divider network - nothing less, nothing more.  If
you have a problem here, one or more of the resistors involved is wrong,
or the voltage from the 8 volt regulator is not correct.

The RF Gain control is one of those resistors, so be certain it is set
to the full clockwise position.

73,
Don W3FPR

Matthew Denson wrote:

> Hi All,
>
> I am building my K2 and have reached the initial checkout steps before building the receiver.
>
> On page 48 of my manual (Rev G if that matters) the instructions say to "Adjust R1 for a reading of 3.80...."
>
> On my K2 the way it is right now the range of voltages I get by changing R1 is 2.1-3.28Vdc.  Hmmm?
>
> I looked at the schematic on the way to work today (I'm still there) and it doesn't look like there are that many variables here.  It is a simple voltage divider of the 8v regulated voltage to ground as far as I can see and it seems like the max voltage should be 1/2 of 8V when R1 is completely shorted out.  I haven't checked the 8V source cause I haven't been back home.  
>
> Maybe extra useless info - I don't know how the internal volt meter works but it is reading out correctly (that is I get the same reading as my DMM where I have made identical measurements) so I assume that the 5V regulator is working right.
>
> Any thoughts on which points to check?  Is my reading of the schematic too simplistic?
>

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[David Woolley (E.L)]

Matthew Denson wrote:
>
> Is the voltage out of the regulator within the expected tolerance?
> Is it a problem that I have maxed out the trimmer pot to get 3.7v or is that expected?

I think this is a bug in the manual.  See:
<http://mailman.qth.net/pipermail/elecraft/2007-June/070302.html>.

--
David Woolley
Emails are not formal business letters, whatever businesses may want.
RFC1855 says there should be an address here, but, in a world of spam,
that is no longer good advice, as archive address hiding may not work.
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