Collins 75A-4 Performance Test

Collins 75A4

Collins 75A-4

Band MDS Blocking Two-tone D.R.
(20 kHz) (20 kHz)
 
80 meters -141 dBm 102 dB 79 dB
40 meters -141 dBm 100 dB 77 dB
20 meters -141 dBm 98 dB 75 dB

AM Audio S/N: 48 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
 
-3 dB -1 dB 0 dB 0 dB 0 dB 0 dB -1 dB -12 dB -44 dB -46 dB -48 dB

AM Audio Distortion:

 
Mod% 100 Hz 200 Hz 400 Hz 600 Hz 800 Hz 1 kHz 2 kHz
 
30% 4.5% 1.4% 1.0% 1.0% 1.0% 0.9% 1.0%
50% 3.2% 1.0% 0.8% 0.8% 0.8% 0.8% 0.7%
70% 2.8% 0.7% 0.7% 0.7% 0.7% 0.8% 0.7%
90% 5.0% 4.0% 4.5% 5.0% 4.5% 2.8% 1.2%
100% 8.9% 7.1% 7.9% 7.9% 7.1% 5.6% 2.0%

Notes: Maximum i-f bandwidth is about 6 kHz @ -6 dB with the stock Collins AM filter.

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. Also there is the usual increase in audio distortion as the modulation percentage increases. This is due to the detector's inability to cleanly demodulate the higher amplitude levels.