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Classic Radio Response Curves

With the exception of the three Fisher AM80 sweeps at the bottom of this page, these were all generated by Allen Lein on his radios. He shoots the different response curves with a film camera so that he can display them together as one image.

Al's sweep generators have built-in bias supplies so he can apply enough negative voltage to the AGC bus to bring all the curves to the same level on the graph. The response curves for the Fisher AM80, were NOT the result of "clamped" AGC voltage. The output of the signal generator was left untouched so it's easy to see how the sensitivity dropped as the bandwidth of the receiver was widened.

The R390 AGC was held at minus six volts for all four sweeps. The gain doesn’t fall off when the bandwidth is widened like it does with the Scotts. The Philharmonic waveforms were obtained by applying AGC varying from minus seven to minus 20 volts to keep them the same height. The BC-779-A (Hammarlund SP-200) has the most gain at a middle setting and falls off somewhat at the narrow and wide ends. The 1937 Philcos don’t change very much at all. The R390 has six IF stages!
To see more of Al Lein's test equipment go to museumofbroadcasting.org/Lein.html.
To see more about earley sweep generators and wobbulators go to museumofbroadcasting.org/wobbulator.html.



BC-779-A
with fixed bias of -10 volts at all three bandwidth positions

BC-779-A
Narrow (2.3 kHz) with -10.6 volts bias
Half (5.4 kHz) with -12 volts bias
Wide(15.4 kHz) with -8.9 volts bias


Scott AW23
Narrow (1.6 kHz) with - 19.3 volts bias
Half (14.8 kHz) with - 7.5 volts bias
Wide (25 kHz) with - 3.0 volts bias


Scott Philharmonic
Narrow (2.0 kHz) with -20 volts bias
Half (8.5 kHz) with -12 volts bias
Wide(21.3 kHz) with -7 volts bias


Collins R390
at 1kHz, 4kHz, 8kHz, & 16 kHz
Response curves made with AGC held at -6 volts

Fisher AM80 sweeps with no external bias applied
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