I am using the AD8307 log converter at 21MHz. I have tested 4 samples and in each case the conversion factor is between 12 and 15mV/dB, not the specified 25mV/dB. Otherwise it works extremely well.
Is the product behaviour likely to deviate from the spec to this extent?
The measurement seems to be straightforward, what could I be doing wrong? The op measurement is a simple dc measurement. The input is from a MOSFET source follower driven from a simple antenna, receiving rf from a transmitter with calibrated op level, so that an input power ratio can be accurately defined. The converter is operating in mid range and this conversion factor is consistent in the "linear" range.
Advice would be much appreciated.