what is the topology of this receiver?

[zorro]

You get a modulated signal at intermediate frequency, like in any other superheterodyne receiver. But this structure of mixer gives a good suppression of the image.
In this case is the modulation is AM, but the same topology works as well for any modulation, analog or digital.
The signal is filtered in IF for attenuate the adjacent channels and then detected.
Again, in this case the detector is a standard AM envelope demodulator.
¿Is it clear?

Z

 

[Borber]

Few words about image rejection mixers can be found here:
https://www.qsl.net/va3iul/RF Mixers/RF_Mixers.pdf

These mixers remove image frequencies but not the carrier or sideband frequencies. Removing carrier from IF will require it's restitution when demodulating signal.
Using mixers with other concepts than superheterodyne is different thing.

 

[neazoi]

Few words about image rejection mixers can be found here:
https://www.qsl.net/va3iul/RF Mixers/RF_Mixers.pdf

These mixers remove image frequencies but not the carrier or sideband frequencies. Removing carrier from IF will require it's restitution when demodulating signal.
Using mixers with other concepts than superheterodyne is different thing.

The confusion happens, because this is a hybrid design.
All right, to put it the other way, if the schematic of this AM RX was not using an IF, but converted directly to the audio (without any changes to the I/Q mixer apart from the requirement of the LO to operage at the RX frequency), then the image signal would be the opposite sideband and this would be suppressed along with the carrier, wouldn't it?

 

[Borber]

In a case you are not using IF you do not need image rejection filter because you are not using concept of soperheterodyne.

 

[neazoi]

In a case you are not using IF you do not need image rejection filter because you are not using concept of soperheterodyne.

Please see post #23. This is the actual question.

 

[zsolt1]

Hi,
it's a sincrodyne receiver . The principle was commonly used in by radio amateurs . Now days it's not practical to use .

 

[neazoi]

Hi,
it's a sincrodyne receiver . The principle was commonly used in by radio amateurs . Now days it's not practical to use .

It is not synchrodyne. From wikipedia: A direct-conversion receiver (DCR), also known as homodyne, synchrodyne, or zero-IF receiver.

This is NOT a zero IF RX. It is a hybrid design, a superheterodyne, with a image rejection front end mixer, instead of following filters.

 

[vfone]

Yes, this is not a direct conversion (or synchrodyne, or zero-IF) receiver. It's a superheterodyne (455kHz IF) using an image reject mixer.
The concept is used by the latest professional or semi-professional HF receivers or transceivers. The biggest issue of this approach is that slightly phase change in the mixer will damage the image rejection.
As can be seen from the schematic there are no inductors or transformers near the mixer, this to make a flat phase response vs frequency.

 

[neazoi]

Yes, this is not a direct conversion (or synchrodyne, or zero-IF) receiver. It's a superheterodyne (455kHz IF) using an image reject mixer.
The concept is used by the latest professional or semi-professional HF receivers or transceivers. The biggest issue of this approach is that slightly phase change in the mixer will damage the image rejection.
As can be seen from the schematic there are no inductors or transformers near the mixer, this to make a flat phase response vs frequency.

The thing on post #23 is my issue now. It relates to the cancellation of the opposite sideband and the carrier in the DCR compared to this receiver.

 

[Borber]

DCR of AM signal is realized in synchronous AM demodulator. Oscillator signal is regenerated from remais of carrier signal to be exact equal frequency not to produce BFO interference effect.

 

[zsolt1]

I'm not familiar with the Ne612 cip , if you guys say so... Anyway this topology is very different from the classic superhet i used to know (like LC tuned circuit for imput, RF amp, mixer,local oscillator,IF amp, detector and finally the AF stage).Interesting circuit