Elecraft

K2 receiver problem - AGC alignment, CAL S LO/HI

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GS-3

K2 receiver problem - AGC alignment, CAL S LO/HI

Hi list,
hi all those who answered my first question.

I had 4V at Pin5 U2. So I replaced R1 with a pot of 50k and set it to 3.65,
3.72 and 3.8V. It got better for sure. The difference between AGC on and off
is in all cases noticable, but slightly. But I think it's significant,
because...

When I CAL S LO and exit it then immediately 1-2 bars of the s-meter start
lighting. So I guess AGC sets in. And this should not be the case, I guess?
Any idea?

Have a nice day,

Gerhard

----- Original Message -----
From: "Don Wilhelm" <[hidden email]>
To: "GS" <[hidden email]>
Sent: Wednesday, November 09, 2005 3:35 PM
Subject: RE: RE: [Elecraft] K2 receiver problem

> Gerhard,
>
> If you have a K2 with serial number greater than 3000, the AGC adjustment
> pot is on the Control Board near the right end - the designation is R1.
>
> For K2 with SN under 3000, there is no pot, and R1 is a fixed resistor.
> Same procedure applies - change the value of R1 to set the AGC threshold.
> It is easy to substitute a temporary pot (50K will do fine) to make the
> adjustment - once the right value is found, solder in the closest value
> fixed resistor.
>
> In my experience, the fixed resistor that one would end up with will vary
> between 33K at the low end and 47k at the high end.
>
> BTW, if this receiver has worked properly before and suddenly developed

this
> problem, look more closely for a failed component - it will likely be in
the

> AGC area - see the control board schematic in the lower left corner.
>
> 73,
> Don W3FPR
>
> > -----Original Message-----
> > From: GS [mailto:[hidden email]]
> > Sent: Wednesday, November 09, 2005 9:48 AM
> > To: [hidden email]
> > Subject: Ant: RE: [Elecraft] K2 receiver problem
> >
> >
> > Hi Don,
> >
> > I can't find how to set the AGC threshold for optimum
> > receiver sensitivity, neither in the manual nor is
> > there any hint in the circuit. At least not for me ;-)
> >
> > Only threshold mentioned in the manual is for the
> > NB...
> >
> > WHAT do I have to adjust to achieve max. voltage at U2
> > pin 5, ctrl board?
> >
> > Thanks!!!
> >
> > Gerhard
> >
> >
> > --- Don Wilhelm <[hidden email]> schrieb:
> >
> > > Gerhardt,
> > >
> > > It sounds like the AGC Threshold is not set
> > > properly.
> > >
> > > I would proceed by first checking the alignment of
> > > the bandpass filters in
> > > Transmit mode (at 2 watts) and then set the AGC
> > > Threshold for optimum
> > > receiver sensitivity - with no antenna connected and
> > > AF and RF Gains set to
> > > max, adjust for the highest voltage at Control Board
> > > U2 pin 5 which yields
> > > no change in the audio noise when switching the AGC
> > > between OFF and ON.
> > > That will usually result in a voltage in the range
> > > of 3.65 to 3.8 volts at
> > > U2 pin 5. Set the S-meter end points (CAL S Hi and
> > > CAL S-Lo) after setting
> > > the threshold.
> > >
> > > If that does not cure the problem, then look for a
> > > problem in the IF receive
> > > chain - that will be where the signal tracing is
> > > required, follow the
> > > p[rocedure for receiver signal tracing in the
> > > Troubleshooting appendix of
> > > the K2 manual.
> > >
> > >
> > > 73,
> > > Don W3FPR
> > >
> > > > -----Original Message-----
> > > >
> > > > got a K2 from another OM on my workbench. It's got
> > > a
> > > > receiver problem and I just want to make sure I do
> > > the
> > > > checks in the correct order and I'm looking for
> > > hints,
> > > > if available!
> > > >
> > > > Thanks in advance!
> > > >
> > > > So here's the problem and what I want to do. It
> > > seems
> > > > the receiver runs with "handbrake on". So the
> > > s-meter
> > > > shows 3 bars without an antenna but the rf gain is
> > > > fully clockwise. I can reduce signals to zero
> > > (using
> > > > RF gain) with this K2 which I can't using my own
> > > K2.
> > > > So mine has a higher sensitivity.
> > > >
> > > > Any idea what's wrong?
> > > >
> > > > What I want to do:
> > > > - s-meter alignment
> > > > - I.F. amplifier alignment
> > > > - (maybe band pass alignment)
> > > > - signal tracing receiver and synthesizer
> > > >
> > > > Kind regards
> > > >
> > > > Gerhard
> > > > DH3FAW
> > > >
> > >
> > >
> >
> >
> >
> >
> >
> >
> >
> > ___________________________________________________________
> > Gesendet von Yahoo! Mail - Jetzt mit 1GB Speicher kostenlos -
> > Hier anmelden: http://mail.yahoo.de
> >
> >
> > --
> > No virus found in this incoming message.
> > Checked by AVG Free Edition.
> > Version: 7.1.362 / Virus Database: 267.12.8/163 - Release Date:

11/8/2005
> >
> >
>

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Don Wilhelm-3

RE: K2 receiver problem - AGC alignment, CAL S LO/HI

Gerhardt,

If you still have a difference between AGC on and off at 3.65 volts or
lower, I would hesitate to go further, but you certainly can try it and see
what happens - no real harm will come from a lower threshold voltage.

After setting the threshold, then adjust CAL S LO first and then CAL S HI
(the order is important, they interact). It is not unusual to have to do
these several times in succession to get it correct. The low S meter
response may vary with the filter width and mode, so check all modes with
the widest filter for each mode.

73,
Don W3FPR

> -----Original Message-----
>
> Hi list,
> hi all those who answered my first question.
>
> I had 4V at Pin5 U2. So I replaced R1 with a pot of 50k and set
> it to 3.65,
> 3.72 and 3.8V. It got better for sure. The difference between AGC
> on and off
> is in all cases noticable, but slightly. But I think it's significant,
> because...
>
> When I CAL S LO and exit it then immediately 1-2 bars of the s-meter start
> lighting. So I guess AGC sets in. And this should not be the
> case, I guess?
> Any idea?
>
> Have a nice day,
>
> Gerhard
>
>

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GS-3

Re: K2 receiver problem - AGC alignment, CAL S LO/HI

OK,

I did it for several modes and there are differences which I will leave for
now. Aimed for 3.65 volts at U2 now. Result seems satisfactory to the ear.

Today in the evening we will use a signal generator and a variable
attenuator to test sensitivities of my K2 and this other one.

If results should not be ok I'll let you now.

Thanks so far for all the help!

Gerhard

----- Original Message -----
From: "Don Wilhelm" <[hidden email]>
To: "Gerhard Schwanz" <[hidden email]>; <[hidden email]>
Cc: <[hidden email]>
Sent: Friday, November 11, 2005 12:37 PM
Subject: RE: K2 receiver problem - AGC alignment, CAL S LO/HI

> Gerhardt,
>
> If you still have a difference between AGC on and off at 3.65 volts or
> lower, I would hesitate to go further, but you certainly can try it and
see

> what happens - no real harm will come from a lower threshold voltage.
>
> After setting the threshold, then adjust CAL S LO first and then CAL S HI
> (the order is important, they interact). It is not unusual to have to do
> these several times in succession to get it correct. The low S meter
> response may vary with the filter width and mode, so check all modes with
> the widest filter for each mode.
>
> 73,
> Don W3FPR
>
> > -----Original Message-----
> >
> > Hi list,
> > hi all those who answered my first question.
> >
> > I had 4V at Pin5 U2. So I replaced R1 with a pot of 50k and set
> > it to 3.65,
> > 3.72 and 3.8V. It got better for sure. The difference between AGC
> > on and off
> > is in all cases noticable, but slightly. But I think it's significant,
> > because...
> >
> > When I CAL S LO and exit it then immediately 1-2 bars of the s-meter

start

> > lighting. So I guess AGC sets in. And this should not be the
> > case, I guess?
> > Any idea?
> >
> > Have a nice day,
> >
> > Gerhard
> >
> >
>

___________________________________________________________
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_______________________________________________
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Post to: [hidden email]
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Don Brown-4

Re: K2 receiver problem - AGC alignment, CAL S LO/HI

In reply to this post by GS-3

Hi

The last K2 I built had strange AGC and S-meter operation that sounds like
the one you are working on. The problem was I had skipped installing the
toroid RFC11 on the bottom of the board. It is amazing the K2 worked at all
but it received fairly well. I could even hear the 1 uV signal from the XG2.
Anyway installing the RFC solved the problem. May be worth a look to see if
you have the same problem

Don Brown
KD5NDB

----- Original Message -----
From: "Gerhard Schwanz" <[hidden email]>
To: <[hidden email]>
Cc: <[hidden email]>
Sent: Friday, November 11, 2005 2:23 AM
Subject: [Elecraft] K2 receiver problem - AGC alignment, CAL S LO/HI

> Hi list,
> hi all those who answered my first question.
>
> I had 4V at Pin5 U2. So I replaced R1 with a pot of 50k and set it to
> 3.65,
> 3.72 and 3.8V. It got better for sure. The difference between AGC on and
> off
> is in all cases noticable, but slightly. But I think it's significant,
> because...
>
> When I CAL S LO and exit it then immediately 1-2 bars of the s-meter start
> lighting. So I guess AGC sets in. And this should not be the case, I
> guess?
> Any idea?
>
> Have a nice day,
>
> Gerhard
>
>
> ----- Original Message -----
> From: "Don Wilhelm" <[hidden email]>
> To: "GS" <[hidden email]>
> Sent: Wednesday, November 09, 2005 3:35 PM
> Subject: RE: RE: [Elecraft] K2 receiver problem
>
>
> > Gerhard,
> >
> > If you have a K2 with serial number greater than 3000, the AGC
> > adjustment
> > pot is on the Control Board near the right end - the designation is R1.
> >
> > For K2 with SN under 3000, there is no pot, and R1 is a fixed resistor.
> > Same procedure applies - change the value of R1 to set the AGC
> > threshold.
> > It is easy to substitute a temporary pot (50K will do fine) to make the
> > adjustment - once the right value is found, solder in the closest value
> > fixed resistor.
> >
> > In my experience, the fixed resistor that one would end up with will
> > vary
> > between 33K at the low end and 47k at the high end.
> >
> > BTW, if this receiver has worked properly before and suddenly developed
> this
> > problem, look more closely for a failed component - it will likely be in
> the
> > AGC area - see the control board schematic in the lower left corner.
> >
> > 73,
> > Don W3FPR
> >
> > > -----Original Message-----
> > > From: GS [mailto:[hidden email]]
> > > Sent: Wednesday, November 09, 2005 9:48 AM
> > > To: [hidden email]
> > > Subject: Ant: RE: [Elecraft] K2 receiver problem
> > >
> > >
> > > Hi Don,
> > >
> > > I can't find how to set the AGC threshold for optimum
> > > receiver sensitivity, neither in the manual nor is
> > > there any hint in the circuit. At least not for me ;-)
> > >
> > > Only threshold mentioned in the manual is for the
> > > NB...
> > >
> > > WHAT do I have to adjust to achieve max. voltage at U2
> > > pin 5, ctrl board?
> > >
> > > Thanks!!!
> > >
> > > Gerhard
> > >
> > >
> > > --- Don Wilhelm <[hidden email]> schrieb:
> > >
> > > > Gerhardt,
> > > >
> > > > It sounds like the AGC Threshold is not set
> > > > properly.
> > > >
> > > > I would proceed by first checking the alignment of
> > > > the bandpass filters in
> > > > Transmit mode (at 2 watts) and then set the AGC
> > > > Threshold for optimum
> > > > receiver sensitivity - with no antenna connected and
> > > > AF and RF Gains set to
> > > > max, adjust for the highest voltage at Control Board
> > > > U2 pin 5 which yields
> > > > no change in the audio noise when switching the AGC
> > > > between OFF and ON.
> > > > That will usually result in a voltage in the range
> > > > of 3.65 to 3.8 volts at
> > > > U2 pin 5. Set the S-meter end points (CAL S Hi and
> > > > CAL S-Lo) after setting
> > > > the threshold.
> > > >
> > > > If that does not cure the problem, then look for a
> > > > problem in the IF receive
> > > > chain - that will be where the signal tracing is
> > > > required, follow the
> > > > p[rocedure for receiver signal tracing in the
> > > > Troubleshooting appendix of
> > > > the K2 manual.
> > > >
> > > >
> > > > 73,
> > > > Don W3FPR
> > > >
> > > > > -----Original Message-----
> > > > >
> > > > > got a K2 from another OM on my workbench. It's got
> > > > a
> > > > > receiver problem and I just want to make sure I do
> > > > the
> > > > > checks in the correct order and I'm looking for
> > > > hints,
> > > > > if available!
> > > > >
> > > > > Thanks in advance!
> > > > >
> > > > > So here's the problem and what I want to do. It
> > > > seems
> > > > > the receiver runs with "handbrake on". So the
> > > > s-meter
> > > > > shows 3 bars without an antenna but the rf gain is
> > > > > fully clockwise. I can reduce signals to zero
> > > > (using
> > > > > RF gain) with this K2 which I can't using my own
> > > > K2.
> > > > > So mine has a higher sensitivity.
> > > > >
> > > > > Any idea what's wrong?
> > > > >
> > > > > What I want to do:
> > > > > - s-meter alignment
> > > > > - I.F. amplifier alignment
> > > > > - (maybe band pass alignment)
> > > > > - signal tracing receiver and synthesizer
> > > > >
> > > > > Kind regards
> > > > >
> > > > > Gerhard
> > > > > DH3FAW
> > > > >
> > > >
> > > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > ___________________________________________________________
> > > Gesendet von Yahoo! Mail - Jetzt mit 1GB Speicher kostenlos -
> > > Hier anmelden: http://mail.yahoo.de
> > >
> > >
> > > --
> > > No virus found in this incoming message.
> > > Checked by AVG Free Edition.
> > > Version: 7.1.362 / Virus Database: 267.12.8/163 - Release Date:
> 11/8/2005
> > >
> > >
> >
>
>
>
>
>
>
> ___________________________________________________________
> Gesendet von Yahoo! Mail - Jetzt mit 1GB Speicher kostenlos - Hier
> anmelden: http://mail.yahoo.de
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>