I recently came across a 15-minute video presentation from Analog Devices about cutting edge radio receivers and I have embedded it at the end of the post. I think anyone with an interest in RF technology will find it of interest.
The image above shows the evolution of receivers.
A) We have the Superhet receiver which was the stable design for many decades. In amateur radio transceivers, there were usually two IF (intermediate frequency) stages... one often around 8-9 MHz and the second one at 455 kHz. Anyone who has a radio from say the 1980's or 1990's will probably have this design. Functional but complex and expensive.
B) We have the more modern Zero IF or No IF design. A digital local oscillator generates two local oscillator signals with one 90 degrees out of phase relative to the other one. These are fed to two mixers which then generates an I and Q signal which are at baseband. These signals are then converted into a digital signal by two ADC's (Analogue to Digital Convertors). There is no IF stage. Many modern receivers use this design.
C) The most recent development is to directly sample the RF signal with no mixers at all. Essentially the signal comes into a RF filter, then a low noise amplifier and then it goes to the ADC where it get's converted into a digital stream.
This images above is a screenshot from the video presentation and it shows the modern generation of Direct RF receivers going up to 18 GHz! I still find it amazing that an IC can sample RF signals in the tens of MHz range let along going all the way to 18 GHz.
Needless to say, all of this cutting else stuff is expensive and is aimed at commercial and military users but it shows the direction of travel. In time, the technology will trickle down and will appear in lower cost products.
Video... The main part of the video is from 3:10 to 7:30 if you want to skip ahead. The second half of the video after 7:30 is about the most recent Analog Devices product.
