3 ms·

Here's a super crude ELI5, feel free to correct me. Signals crash course: Radio comms have a channel they need to fit into (let's say 1.1GHz - 1.2GHz as an exa

Here's a super crude ELI5, feel free to correct me. Signals crash course: Radio comms have a channel they need to fit into (let's say 1.1GHz - 1.2GHz as an example). This means that what you send over the air is basically a high frequency (~1.15GHz) sine wave. You encode data by slowly varying this sine wave (amplitude and/or frequency). The variations are going to be super slow, as fast changes in either amplitude or frequency will make your signal go outside the frequency limits. It's only the sine wave (aka the "carrier frequency") that's high frequency (1.15GHz in our case). There are several ways to digitize this signal. You can do "direct RF sampling" - you need a very high sampling rate (2.4GHz+ due to Nyquist in our case) and just sample the high frequency signal. You can multiply (in analog domain) the RF signal from the antenna by another frequency to keep all the slow changes but change the carrier frequency. This means that you don't need such a high lower sampling rate (you can get away with much less than GHz). If your new carrier frequency is just some low but non-zero frequency, that's super-heterodyne (IF). If it's zero, that's Zero-IF.

mwbajor 3y ago
Yes all correct, you didn't capture any of the tradeoffs but thats the basic idea.
gorkish 3y ago
Just have to say this is the first time I've seen someone introduce the concept of an RF mixer "backwards".
kurthr 3y ago
I was surprised they didn't use the word homodyne. One issue they didn't mention, but probably shows up in the noise figures is that homodyne receivers suffer from 1/f noise in the relatively wide band "direct conversion" amplifiers. Of course all of the heterodyne receivers suffer from 1/f up-conversion at the mixer.
- teleforce 3y ago
  It is rather a soup of terminologies namely homodyne, zero-IF, and direct conversion architecture are all referring to the same thing. It seems they are now settling on RF sampling for the newer transciever architecture technology but sometime direct RF is also being used for example this latter terminology is referred by Intel for their new line of FPGA and RF transceivers product integration.
ipdashc 3y ago
This is the first time I've seen it explained like this, and having struggled with these concepts in the past, I found your explanation really easy to understand. Thanks!

mwbajor 3y ago

Yes all correct, you didn't capture any of the tradeoffs but thats the basic idea.

gorkish 3y ago

Just have to say this is the first time I've seen someone introduce the concept of an RF mixer "backwards".

kurthr 3y ago

I was surprised they didn't use the word homodyne. One issue they didn't mention, but probably shows up in the noise figures is that homodyne receivers suffer from 1/f noise in the relatively wide band "direct conversion" amplifiers. Of course all of the heterodyne receivers suffer from 1/f up-conversion at the mixer.

teleforce 3y ago
It is rather a soup of terminologies namely homodyne, zero-IF, and direct conversion architecture are all referring to the same thing. It seems they are now settling on RF sampling for the newer transciever architecture technology but sometime direct RF is also being used for example this latter terminology is referred by Intel for their new line of FPGA and RF transceivers product integration.

ipdashc 3y ago

This is the first time I've seen it explained like this, and having struggled with these concepts in the past, I found your explanation really easy to understand. Thanks!