Drake R-4A Receiver Performance Test

Drake R-4A

Drake R-4A

Band MDS Blocking Two-tone D.R.
(20 kHz) (20 kHz)
 
80 meters -137 dBm 121 dB 87 dB
40 meters -137 dBm 122 dB 88 dB
20 meters -136 dBm 123 dB 88 dB

AM Audio S/N: 45 dB




AM Audio Frequency Response:

 
100 Hz 200 Hz 400 Hz 600 Hz 800 Hz 1 kHz 2 kHz 3 kHz 4 kHz 5 kHz 6 kHz
 
-33 dB -21 dB -3 dB 0 dB 0 dB 0 dB -4 dB -10 dB -23 dB -32 dB -40 dB

AM Audio Distortion:

 
Mod% 100 Hz 200 Hz 400 Hz 600 Hz 800 Hz 1 kHz 2 kHz
 
30% - - 14% 7.9% 5.6% 4.0% 2.8%
50% - - 16% 11% 8.9% 6.3% 4.0%
70% - - 18% 14% 13% 7.9% 5.0%
90% - - 20% 16% 14% 10% 5.6%
100% - - 20% 16% 14% 10% 5.6%

Notes: AM frequency response was fairly restricted due to the 4.8 kHz maximum i-f bandwidth. AM distortion numbers show the somewhat typical increase at lower audio frequencies - most often caused by the low audio frequencies riding on the AGC line. The audio response rolls off rather quickly on the low end. A frequency response test was run on just the audio output stage which confirmed the tiny audio output transformer to be responsible for the poor low frequency audio performance.

Note that this must have been a 'late' R-4A since the product detector, AM detector, agc and audio preamplifier stages are solid state as in the R-4B. Did not investigate why the AM distortion measurement results were so bad other than to verify all appropriate circuit components were in working order.