The discrete transistor Gilbert cell mixer which is briefly tested a month before, is that mixer really having a decent performance? Let's compare it with a classic, popular NE602 mixer. Because both mixer do not have 50 ohm output impedance so this time a 4:1 transformer is added to make it more match with the 50 ohm spectrum analyzer.
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The board for mixer comparison is consist of upper section discrete Gilbert cell and lower section of NE602 mixer. Left side is RF and LO input connector and the output connector is on the right side.
The 1.6 mm board is a mistake, 1.2 mm would be better.
Transistor Gilbert cell under test, with LO input 27MHz -20dbm and RF input 32MHz -20dbm,
beside the wanted 5MHz mixing product, many other frequency component is observed.
With same input signal. The NE602A mixer give way less spurious component, but the mixing product also lower in power. This may caused by the bias current of NE602 is smaller than the discrete mixer. It is observed that the LO isolation in NE602 is better.
This comparison attempt did not draw any conclusion, further analyst and more test is required to be done.
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