The MC1496 Is Now Quadrature SDR QSD In One Chip: http://groups.yahoo.com/group/soft_radio/files/SDR%20Spice%20Analysis%20Files/MC1496_QSD.zip
Also at LTSpice Group: http://tech.groups.yahoo.com/group/LTspice/files/%20Examples/Educational/I-Q_modulation/SDR_I-Q_LTSpice.zip I have uploaded a working LTSpice model of the idea of the MC1496 balanced modulator split and redesigned into dual mixers. The file demonstrates a working QSD with the I and Q inputs mixed with a offset signal input that is offset from the I and Q by 12 kHz. I use 1 MHz for the I and Q inputs and 1.012 MHz for the injection (modulation) signal. At the output you can see the fully mixed signal and the I and Q carriers being modulated by the 12 kHz offset. This circuit will double as a phase modulator for SDR two way radio and so we can go and get some home brew two way radios going. Please note, this circuit is rated for 100 MHz and under uses but, it works up to 200 MHz and so you can use this up on 2 meters. I added compensation to control the gain and make the bandwidth better. It works well up around 150 MHz with some loss but add some gain and you will "get her done." I have spent some time determining the input and output impedances of the chip being used in this new way. I have adjusted the bias of the transistor inputs carefully for best waveform and linearity. I will refine it some more if possible but it is working good now. As far as using this in receiver hardware? Well hell, why not? I hope I have kept the waveform distortion and noise down, but we shall see. I have bypassed some noise to ground in the circuit. Particularly on the bias adjustment. I hope you like this file. Dan ka9rza
