Tim, please have a look on my folder (DK5LV) subfolder "LTSPICE
XVII" in the BITX 20 group. I have made simulations of the AF
preamp, the gain ist 46 dB.? I can confirm that the LTSPICE
simulations comply with measurements I made using my BITX40.
In the subfolder "BITX40 level diagramme" You can find my level
diagramme. I can confirm that my assumptions on the gain of the
stages in the BITX 40 comply with the measurements of my BITX 40.
This means that the AF preamp is momentarily the stage which
limits the distortion free dynamic range of the complete BITX40.
The high gain of the audio string is necessary to get a suitable
overlal audio power. To put an AGC system between the output of
the AF preamp and the LM386 does not improve the ability of the
BITX 40 for? a maximum distortionless RF antenna input signal.?
Henning Weddig
DK5LV
Am 10.02.2018 um 22:18 schrieb Tim
Gorman:
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Does anyone know
what the typical output level of the first AF amp should be for a
strong signal? I built the AGC amp shown in the message by Joe
Puma and the AF output begins to distort with an input of 300mv to
350mv RMS. I haven't yet built a spreadsheet to see how much AGC
action is provided as the AF level goes up. Maybe I can get to
that tomorrow. I don't have any way to sweep the amplitude of the
input AF, only the frequency. So I'll have to build everything up
manually a point at a time in order to see what compression is
provided.?
