Post History
I want to make a simple 7MHz direct conversion SSB receiver in order to materialize some RF concepts I have been teaching myself lately. My question revolves around the mixer portion. I'm failing t...
#3: Post edited
by
jm567
·
2020-10-06T16:29:38Z (about 4 years ago)
I want to make a simple 7MHz direct conversion SSB receiver in order to materialize some RF concepts I have been teaching myself lately. My question revolves around the mixer portion. I'm failing to understand how the audio is extracted from the carrier wave and googling it gives me either 10 pages of hello world RF-LO and RF+LO IF output examples or a bunch of trigonometric vomit. Since the 40M amateur band I want to receive spans from 7MHz to 7.3MHz, lets suppose I begin tuning in at 7MHz flat. In a DCR model, the LO oscillates at nearly the same frequency as the incoming carrier wave. Lets say I have chosen an LO of 7MHz. In this case I would get a 7MHz - 7MHz and a 14MHz sine wave on the output according to Google University. But what happens next? It looks like I just have a 14MHz sine wave on the output and if I adjust the LO to increase I would get a 14MHZ + Xadjust and a 0HZ + Xadjust signal on the output? How is this useful? Where is the audio? How is it extracted from this IF output? Sorry for the somewhat vague question.
- I want to make a simple 7MHz direct conversion SSB receiver in order to materialize some RF concepts I have been teaching myself lately. My question revolves around the mixer portion. I'm failing to understand how the audio is extracted from the carrier wave.
- Lets suppose I want to listen to an audio signal that rides on a 7MHz carrier wave. What would my LO, or BFO frequency in this case, oscillate at? Would it be 7MHz and then would I need a 300KHz tuning range to listen to the full band of signals? Thanks.
#2: Post edited
by
Olin Lathrop
·
2020-10-05T17:48:46Z (about 4 years ago)
Removed fluff
Hello,I want to make a simple 7MHz direct conversion SSB receiver in order to materialize some RF concepts I have been teaching myself lately. My question revolves around the mixer portion. I'm failing to understand how the audio is extracted from the carrier wave and googling it gives me either 10 pages of hello world RF-LO and RF+LO IF output examples or a bunch of trigonometric vomit. Since the 40M amateur band I want to receive spans from 7MHz to 7.3MHz, lets suppose I begin tuning in at 7MHz flat. In a DCR model, the LO oscillates at nearly the same frequency as the incoming carrier wave. Lets say I have chosen an LO of 7MHz. In this case I would get a 7MHz - 7MHz and a 14MHz sine wave on the output according to Google University. But what happens next? It looks like I just have a 14MHz sine wave on the output and if I adjust the LO to increase I would get a 14MHZ + Xadjust and a 0HZ + Xadjust signal on the output? How is this useful? Where is the audio? How is it extracted from this IF output? Sorry for the somewhat vague question.Thanks.
- I want to make a simple 7MHz direct conversion SSB receiver in order to materialize some RF concepts I have been teaching myself lately. My question revolves around the mixer portion. I'm failing to understand how the audio is extracted from the carrier wave and googling it gives me either 10 pages of hello world RF-LO and RF+LO IF output examples or a bunch of trigonometric vomit. Since the 40M amateur band I want to receive spans from 7MHz to 7.3MHz, lets suppose I begin tuning in at 7MHz flat. In a DCR model, the LO oscillates at nearly the same frequency as the incoming carrier wave. Lets say I have chosen an LO of 7MHz. In this case I would get a 7MHz - 7MHz and a 14MHz sine wave on the output according to Google University. But what happens next? It looks like I just have a 14MHz sine wave on the output and if I adjust the LO to increase I would get a 14MHZ + Xadjust and a 0HZ + Xadjust signal on the output? How is this useful? Where is the audio? How is it extracted from this IF output? Sorry for the somewhat vague question.
#1: Initial revision
by
jm567
·
2020-10-05T17:02:22Z (about 4 years ago)
Mixers and Audio Extraction in a DCR Architecture
Hello, I want to make a simple 7MHz direct conversion SSB receiver in order to materialize some RF concepts I have been teaching myself lately. My question revolves around the mixer portion. I'm failing to understand how the audio is extracted from the carrier wave and googling it gives me either 10 pages of hello world RF-LO and RF+LO IF output examples or a bunch of trigonometric vomit. Since the 40M amateur band I want to receive spans from 7MHz to 7.3MHz, lets suppose I begin tuning in at 7MHz flat. In a DCR model, the LO oscillates at nearly the same frequency as the incoming carrier wave. Lets say I have chosen an LO of 7MHz. In this case I would get a 7MHz - 7MHz and a 14MHz sine wave on the output according to Google University. But what happens next? It looks like I just have a 14MHz sine wave on the output and if I adjust the LO to increase I would get a 14MHZ + Xadjust and a 0HZ + Xadjust signal on the output? How is this useful? Where is the audio? How is it extracted from this IF output? Sorry for the somewhat vague question. Thanks.