circuit with just a jumper. You may want to measure the filter input and
Solve the filter loss problem first and then look at the AGC. You may be
> -----Original Message-----
>
> Ok about the MC1350 specs, and my noise level is very high, but i
> am afraid
> that with less noise there is a problem.
> I did some more measurements end followed the signal tracing procedure,
> where i find 2 questionable things:
>
> - Crystal filter output seems quite low, it reads 0,17 Vrms,
> instead of the
> given 0,35V .. tried this with different BFO settings, no significant
> difference. The input of the filter is about 2,15 Vrms with a jumper over
> the NB connector (5 dB more than normal)
>
> - AGC @ saturation seems way too low, it reads about 4,3 volts where it
> should be 6,9V.
>
> My opinion is that there is some sort of fault in the AGC circuit, that
> causes no difference in noise level with AGC on or off, and also a big
> difference in audio level between a S3 and a S9+ station.
>
> I have changed C8 a while ago to stop the receive from muting
> with AGC off,
> Is it possible that the ACG oscillator level is too low because of this?
>
> The receive seems to hear well, compared to my FT-1000. Just the big
> difference in audio levels worries me..
>
> Thanks again,
>
>
> Sjoerd
> PE2SVN
>
>
> -----Oorspronkelijk bericht-----
> Van: Don Wilhelm [mailto:
[hidden email]]
> Verzonden: woensdag 30 augustus 2006 14:02
> Aan: Sjoerd;
[hidden email]
> Onderwerp: RE: [Elecraft] K2 AGC problem
>
> Sjoerd,
>
> If you look at the MC1350 data sheet, you will find the AGC
> characteristics
> for operation wiht a 12 volt supply to the chip and that graph indicates
> that the gain changes almost linearly from 0 dB to 20dB with an
> AGC voltage
> change from 5 to 6 volts, or 10 dB for a 500 mV change, and the rate of
> change increases abruptly above the 6 volt level.
>
> However, the K2 uses that IF amplifier chip at an 8 volt supply, so as a
> rough guess, the voltages should be multiplied by a factor of 2/3. I have
> not attempted to characterize this amplifier at an 8 volt supply.
>
> Fact 2 - the gain of the IF Amp is governed by the current rather than the
> voltage into the AGC pin, so you should conclude that there are several
> dependencies that will modify the actual voltage required for a
> given gain.
>
> I would suggest that you set the AGC Threshold somewhere between
> 3.7 and 3.8
> volts as measured at Control Board U2 pin 5. You may end up with some
> slight reduction of gain between AGC on and AGC off, but lower
> voltage here
> will tend to produce problems with CAL S HI and CAL S LO settings. If you
> are willing to live with the consequences of using a voltage
> lower than 3.7
> volts to produce less change between AGC ON/OFF, then you must accept the
> fact that you will have a weaker AGC gain reduction overall, and your
> S-meter may produce readings that are different from the norm.
>
> You may not have any problem at all, only a consequence of the AGC action
> produced by your high noise level.
>
> 73,
> Don W3FPR
>
>
> > -----Original Message-----
> >
> > Hello all,
> >
> > Just some added info abt my K2's problem.
> >
> > Measured Vagc at pin 5 of the IF amp:
> >
> > -No antenna connected AGC on: 3.83V
> > -no antenna connected AGC off: 3.82V
> > -40m antenna connected: 3.90V (my FT-1000D shows abt S5
> > noise)
> > -XG2 connected : 3.99V (50uV level, should be
> > S9)
> >
> > Found a post from N6IZ in 2004 that stated that Vagc varies about
> > 100mV per
> > 10dB. (
> >
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