4 ms·

In terms of the properties of the antenna itself, it is reciprocal -- the "How Antennas Work" part. You comment is more along the lines of "How to Use Antennas

In terms of the properties of the antenna itself, it is reciprocal -- the "How Antennas Work" part. You comment is more along the lines of "How to Use Antennas", that is a different question. The places where there is a benefit to having different antennas for receive and transmit depends on the characteristics of the channel and on the application. The classic example being where a receiving antenna that reduces reception of local noise can give a better signal-to-noise ratio than an antenna that has been optimized for the best transmitted signal footprint at the location of the other station. So, while I agree that in practice there are plenty of times where separate receive and transmit antennas have a benefit, it isn't because of antenna physics.

madengr 7y ago
Case in point is my ham radio station. I have an active magnetic loop for HF RX. This allows me to null out near field interference (a few dB from the transformer in the back yard) and provides very broad bandwidth (VLF thru HF). It is 75 feet from the house, away from that near field interference. TX is an inverted L, up the side of the house, with a tuner at the base. I don’t have electrical length, but I do have power, so I can trade off efficiency for a power amp, and the bandwidth with the tuner. Interference is irrelevant, but I can see some 60 Hz cross modulation on a monitoring receiver, due to coupling to the house wiring.
wglb 7y ago
I think this is incorrect. See my comment at https://news.ycombinator.com/item?id=22790001 https://news.ycombinator.com/item?id=22790001
- dbcurtis 7y ago
  As far as I can tell, you are agreeing with me. It is the channel that is not reciprocal, which is why there is a benefit to separate antennas. Do not confuse the analysis of an antenna in free space with real-world deployment with real ground, noise sources of various kinds, and asymmetrical propagation.

madengr 7y ago

Case in point is my ham radio station. I have an active magnetic loop for HF RX. This allows me to null out near field interference (a few dB from the transformer in the back yard) and provides very broad bandwidth (VLF thru HF). It is 75 feet from the house, away from that near field interference. TX is an inverted L, up the side of the house, with a tuner at the base. I don’t have electrical length, but I do have power, so I can trade off efficiency for a power amp, and the bandwidth with the tuner. Interference is irrelevant, but I can see some 60 Hz cross modulation on a monitoring receiver, due to coupling to the house wiring.

wglb 7y ago

I think this is incorrect. See my comment at https://news.ycombinator.com/item?id=22790001 https://news.ycombinator.com/item?id=22790001

dbcurtis 7y ago
As far as I can tell, you are agreeing with me. It is the channel that is not reciprocal, which is why there is a benefit to separate antennas. Do not confuse the analysis of an antenna in free space with real-world deployment with real ground, noise sources of various kinds, and asymmetrical propagation.