Fortunately I was able to get a NE604. I replace the AN7222 with the ne604. This device really works great. The dynamic range of the 38 MHZ receiver looks good. I measured 30 mV and .2 micro µV that would be 50 db dynamic range. My RF generator can not produce more than 30 mV so I van not verify that the the dynamic range is 60-70 db. It looks good though.
I am going to control the analyzer using a micro controller. This is quite a challenge. One of the problems is the generation of the sawtooth signal that sweeps the LO frequency. It could be done using a DAC. Then the micro controller knows the relationship between voltage and center frequency. It can display this frequency. So far so good. However this DAC needs a lot of bits. 12 bits are needed for 100 KHz steps (500/0.1). For 25 KHz 15 bits are needed. The output has to be very stable and without noise. After all 48mV drift means 1 MHz drift. It may be possible to use this concept but it is too difficult.
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