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Originally Posted by Eldarion
T
As an aside, I wonder why they used two different datapaths on different antennas? Did the old radios do that, or did the two datapaths use the same antenna?
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The eWave design used an RF module made by Uniden for consumer cordless phones. The transmitter and receiver were duplex coupled onto a single antenna.
In both designs, the transmitters are constantly transmitting even when they are not conveying data. One radio transmits around 902MHz, the other around 928MHz.
To find other examples of full duplex operation on a single antenna, look no further than your nearest cordless or cell phone.
The principal is to provide enough isolation between the receiver and transmitter such that the phase noise from the transmitter at the co-located receiver's input doesn't affect the receiver's sensitivity. By isolating the receiver from the transmitter the impedance from one of the tx/rx ports at that ports desired pass frequency will provide a good match to the antenna's impedance and simultaneously provide a high impedance at the opposing tx/rx port. It can be accomplished with a pair of high pass and low pass filters, or could be done with a pass-notch type filter.
The physical seperation between the internal and external antenna provide little in the way of isolation compared to what filters would accomplish, so I suspect that there are still filters present on at least the transmitters, but maybe they felt it was easier than trying to match the the combined port to a single antenna.
IFI clearly had little time to design these radios, so probably took as little design risk as possible, and thus the dual antenna approach.
Clearly they've spent some additional time over these past few weeks working out some software changes, lets hope it resolves the problems some of the teams were experiencing.