Hi, a question for anyone can help. When I connect my dual output directional coupler to AD8302 meter I can not get right measurments execpt I connect 2 same value 10 dB attenuators. Note that with and without attenuators dBm values was inside dynamic range of AD8302. Without attenuators when I terminate each output with a dummy load I see at the other port correct values. But when I connect the AD8302 the values are changing. Note that AD8302 PCB has proper 50 ohm load (52.3 ohm R) as datasheet advises. It is not a AD8302 read error as I put a -20 dB probe at each port and I measure values similar to AD8302. Can anyone can give an explanation of this ?
My thought and also from a friend at QRL was common : the AD8302 SWR meter has SWR !!! (the 50 ohm termination is not really 50 ohm). This was proofed by measuring it in the range of 1.9 - 2.7 GHz. An 20 dB attenuator was used in order not to exceed the 0 dBm max input of AD8302 using a suitable directional coupler. The results are -5 dB (SWR 3.5) at 2.4 GHz , worst reading -2.3 dB (SWR 7.5) and best -8 dB (SWR 2.3) & -10 dB (SWR 1.9) at 1.9 GHz. This seems that infect the readings using a single directional coupler using both output directly to AD8302.