Direct Conversion Transceiver IMD measurements OH7SV 2004-08-20


Fig 1. The 3rd order IMD measurements results

Notes:
The 3rd IMD was measured with three different frequency combinations with equal results. With 20 kHz frequncy spacing the noise floor was distorted by the noise of generators. All measurements were made in 80 m band with the following frequecies:
- RX 3.700 MHz, Genetrator 1 3.720 MHz, Generator 2 3.740 MHz
- RX 3.700 MHz, Genetrator 1 3.740 MHz, Generator 2 3.780 MHz
- RX 3.500 MHz, Genetrator 1 3.600 MHz, Generator 2 3.700 MHz
The IP3 was independent of the gain of AF preamplifier. This amplifier is after the mixer muxer sampling capacitors. Gains of 29 dB and 39 dB were tested.


Fig 2. Measurement setup

Two HP E4420B signal generators were used. Wilkinson splitter is home made with 11 dB loss and better than 30 dB isolation.


Fig 3. Equpiment setup