Electronics > RF, Microwave, Ham Radio

Making sense of this obscure RF module

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igendel:
Hi all,

Someone gave me a box with a ~100 of these modules. No explanation or background were provided, and I have no Analog/RF background myself. The modules were probably in use, around 20 years ago.
To my highly un-trained eye it looks similar to those simple Chinese OOK rf receivers. I bet you know more and can shed light on this.

Here are my observations so far:

- To remove all doubt, the board has only two layers
- The three ground pins are easy enough to spot by looking at the back side. The pin farthest from the IC isn't connected to anything.
- All the the deep-green surfaces with the straight, blackened scratches are trimmed resistors, right?
- The IC is a TI TLC272 Dual OpAmp, so the pins from 1 to 8 are 1OUT, 1IN-, 1IN+, GND, 2IN+, 2IN-, 2OUT and Vdd.
https://www.ti.com/lit/ds/symlink/tlc272.pdf

I removed one to see what's underneath.
The module's rightmost pins are therefore Vdd and Output (from 2OUT). What do the next three do? Are they used for threshold or some gain control by the carrier board?

- What does the third-from-left pin do? Above it are a capacitor(?) and then a transistor. Is this thing a transmitter too?

Thanks, I hope this post belongs here and not in the Complete Noob forum  ;D

PA0PBZ:
It looks like there is no RF oscillator on that board, I think pin 3 is the RF input which is then amplified by the 2 transistors (BF17p?). It seems that the supply voltage for the RF part would be connected to pin 4 but there is a component missing? Looks like an AM receiver, probably 433MHz.

Wait... Have a look at this  :) https://www.gotronic.fr/art-recepteur-am-433-92-ac-rx2-cs-27868.htm



I'd say that's very close.

igendel:

--- Quote from: PA0PBZ on June 09, 2023, 10:38:58 am ---It seems that the supply voltage for the RF part would be connected to pin 4 but there is a component missing? Looks like an AM receiver, probably 433MHz.
--- End quote ---

All the boards have two unpopulated components, one right above the little copper coil, and one connecting the ground plane of that single pin.



--- Quote from: PA0PBZ on June 09, 2023, 10:38:58 am ---Wait... Have a look at this  :) https://www.gotronic.fr/art-recepteur-am-433-92-ac-rx2-cs-27868.htm
I'd say that's very close.

--- End quote ---

Yes, it looks right. I have some cheap 433MHz transmitters, I'll try to hook then up and see if I can receive anything. Thanks!

radiolistener:

--- Quote from: igendel on June 09, 2023, 11:30:58 am ---Yes, it looks right. I have some cheap 433MHz transmitters

--- End quote ---

according to description it's 433 MHz receiver  :)
And your modules looks a little bit different

PA0PBZ:

--- Quote from: igendel on June 09, 2023, 11:30:58 am ---
--- Quote from: PA0PBZ on June 09, 2023, 10:38:58 am ---It seems that the supply voltage for the RF part would be connected to pin 4 but there is a component missing? Looks like an AM receiver, probably 433MHz.
--- End quote ---

All the boards have two unpopulated components, one right above the little copper coil, and one connecting the ground plane of that single pin.


--- End quote ---

Right, I didn't notice the pin was connected to ground. So the VCC must be coming from pin 5 then and the unpopulated part is a decoupling cap. I didn't expect the RF part to be supplied via a printed resistor but so be it.

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