On Tue, 01 Sep 2009 10:01:19 -0700, Michał Słomkowski wrote:

I'm designing a HF transceiver and I'm going to use SA612/NE612 as a
product detector. I'm not sure what is the optimal signal level, which
should be delivered to the inputs from the IF amplifier to achieve the
best performance?

There are graphs for input IP3, compression and gain in
the Philips data-sheet. The exact value of IP3 will
depend on the supply voltage, frequency and the configuration
of your circuit. The data-sheet figure for 45MHz is -13dBm.
You will want the IF input to be well below this level.
Somewhere in the -25 to -40dBm region should be ok.

The xx612 is a low power, high gain device. It is not a
particularly good choice as a product detector in a superhet.
A simple two diode balanced mixer or a diode ring mixer (DBM)
would give much better IMD performance and costs even less than
the 612.

73, Ed. EI9GQ.



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