On Sat, Oct 12, 2019 at 09:06 PM, Bill Hemmings wrote:
Somehow, I don't see a good reason to CARE about matching
receiver input impedance.
it doesn't related with volts or watts, impedance mismatch has the same poor effect for any volts and watts.
Impedance mismatch just reduce signal level. But when you use cable, there is another issue - standing wave in the cable. Standing wave multiplies all losses in the cable. This is why standing wave in the cable leads to dramatic signal loss.
When you use TX, standing wave in the cable depends on cable load impedance (antenna). This is why it is very critical to match your cable with antenna. Note, I wrote cable (not TX output), this is not mistake, you're needs to match your cable impedance with antenna.
When you use RX, standing wave in the cable depends on cable load impedance (receiver input impedance). This is why antenna match is not critical for RX. But for RX you're needs to match your RX input with cable impedance, otherwise you will have the same issue as for TX.
If you use RX with proper impedance match between RX input and cable impedance (both impedances should be equals, for example 50 ohm), there is no standing wave in the cable. If your antenna has bad impedance match with cable, it just will leads to low signal level, but there is no multiple losses and distortions in the cable due to standing wave, because there is no standing wave. Your receiver can use high gain amplifier in order to compensate low signal level from antenna. This is why antenna match is not critical for receiver.
The same output impedance of transmitter is not critical, it just leads to lower efficiency, but there is no multiple losses and distortions due standing wave. Because standing wave is missing when you transmit to antenna which has good match with cable.
