IC-756Pro III Dynamic Tests

by Paolo Odone I1ODP

I recently performed several IP3 and dynamic-range measurements on the IC-756Pro III. Here are the final results:

Test Equipment:

 

Simplified Block Diagram:

Fig. 1. Simplified block diagram of IMD test setup.

Test Conditions:

14 MHz, CW, 500 Hz filter selected, Preamp off, AGC off

Test Setup:

Close-in crystal oscillator frequencies kHz
Test Setup 1 Test Setup 2
f1 = 14205.67 f1 = 14252.11
f2 = 14209.52 f2 = 14256.52
 
Test offset inside 15 kHz roofing filter ( f2 - f1) kHz
3.85 4.41
 
IMD3 Product Frequencies kHz
2f- f1 = 14213.37 2f2 - f1 = 14260.93
2f1 - f= 14201.82 2f1 - f= 14247.70
 
IMD3 Bandwidth kHz
11.55 13.23
Test band centre kHz
14207.595 14254.315
 
Wide-spaced crystal oscillator frequencies kHz
f= 14209.52,  f= 14256.52
 
Test offset ( f2 - f1) kHz
47.00

The 2 crystal oscillators, each with -50 dBm signal power output, were first checked on the selective voltmeter, then connected to the IC-756Pro III input via the combiner. The combiner insertion loss is included in the stated test signal levels. For close-spaced IMD measurement, test signal power = (source output - combiner  insertion loss). Example: If source output = -50 dBm per tone and combiner loss = 3 dB, test signal power = (-50-3)  = -53 dbm per tone, or -47 dBm 2-signal (composite).

The AC voltmeter was connected to the PHONES jack to measure the 3 dB rise in noise floor due to IMD.

MDS =  -131 dBm ( noise + 3dB); thus, noise floor is -134 dBm.

IMD3 Dynamic Range is the difference between MDS and the power level of either of 2 equal test signals applied to the receiver input which yields IMD3 products 3 dB above the noise floor.

Results for 47 kHz offset:

2f1 - f2: Power level of either of 2 equal test signals to raise IMD products 3dB over the noise  = -24 dBm 

IP3 = + 29.5 dBm 

IMD3 Dynamic Range = 107 dB

2f2 - f1: Power level of either of 2 equal test signals to raise IMD products 3dB over the noise = -22 dBm 

IP3 = +32.5 dBm 

IMD3 Dynamic Range = 109 dB

Results for 4.4 kHz offset:

2f1 - f2: Power level of either of 2 equal test signals to raise IMD products 3dB over the noise = -  53 dBm 

IP3 = -15.5 dBm 

IMD3 Dynamic Range = 78 dB

2f2 - f1: Power level of either of 2 equal test signals to raise IMD products 3dB over the noise = -50 dBm

IP3 = - 9.5 dBm 

IMD3 Dynamic Range= 81 dB

I calculated IMD3 Dynamic Range using  -131 dBm MDS as the lower reference.

 

Contents copyright  2005 P. Odone I1ODP. 
Page created & edited by A. Farson VA7OJ/AB4OJ. Last updated: 11/27/2015