K2 AGC Problem

[JIMMY D HARRIS]

Sjoerd,

When measuring millivolts some voltmeters are not very accurate.  I've seen
them err as much as 40-50 percent.  Compare two or three meters and see the
results.  Also, some crystals don't put out a pure sine wave making RMS
measurements less acccurate.  Look at it on an o'scope if one is available
and calculate the RMS from the waveform on the screen.  When working with
millivolts there are a lot of factors that can affect accuracy that are less
of a problem when measuring higher voltages.

Just some observations.  Hope you get it working soon to your satisfaction.

Jim, AB0UK
K2/100  S/N 4787


>- 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)


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[Ron D'Eau Claire-2]

Jim, AB0UK wrote:

When measuring millivolts some voltmeters are not very accurate.  I've seen
them err as much as 40-50 percent.  Compare two or three meters and see the
results.  Also, some crystals don't put out a pure sine wave making RMS
measurements less acccurate.  Look at it on an o'scope if one is available
and calculate the RMS from the waveform on the screen.  When working with
millivolts there are a lot of factors that can affect accuracy that are less

of a problem when measuring higher voltages.

Just some observations.  Hope you get it working soon to your satisfaction.
\------------------

You make an excellent point Jim. One simply cannot measure an RF signal with
a DMM with any accuracy. Even with an "RF Probe" accuracy at low levels will
vary widely because most RF probes use a diode rectifier to provide a DC
voltage for the meter to indicate. Diodes become very non-linear at low
levels.

The best instrument for such measurements is a suitable oscilloscope with an
10:1 isolating probe designed for the frequencies involved.

Ron AC7AC



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