The AM Forum

Receiver: National NC-183D

Band	MDS	Blocking DR	Two-tone DR
		(20 kHz)	(20 kHz)
80 meters	-142 dBm	107 dB	79 dB
40 meters	-142 dBm	110 dB	81 dB
20 meters	-136 dBm	105 dB	83 dB

AM audio S/N: 43 dB

AM Audio Frequency Response: in dB, referenced to 1 kHz measurement   

100 Hz	200 Hz	400 Hz	600 Hz	800 Hz	1 kHz	2 kHz	3 kHz	4 kHz	5 kHz	6 kHz
0	+1	+1	+1	0	0	-6	-18	-28	-39	-47

AM Audio Distortion:

Mod	100 Hz	200 Hz	400 Hz	600 Hz	800 Hz	1 kHz	2 kHz
30%	4.5%	3.2%	2.5%	2.2%	2.2%	2.2%	4.0%
50%	5.0%	3.2%	2.5%	2.5%	2.2%	2.2%	3.2%
70%	6.3%	4.0%	3.2%	3.2%	2.8%	2.8%	4.0%
90%	7.9%	5.0%	4.5%	4.0%	3.5%	3.2%	4.0%
100%	11%	7.1%	6.3%	5.6%	4.5%	3.5%	3.5%

Notes: Maximum i-f bandwidth is about 4 kHz @ -6 dB. Before running the audio frequency response and audio distortion test the tone control was adjusted for flat response as measured through the auxiliary audio input.

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 although this receiver does pretty well.
   

Info on the measurement setups and test results on other receivers can be found at:

http://www.w1vd.com/BAreceivertest.html (http://www.w1vd.com/BAreceivertest.html)