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I cannot find a datasheet for my 433 MHz receiver (which seems to be a XY-MK-5V), which looks like this:

enter image description here

Also, I was wondering what is the use of the screw (on top of the green box with copper wire circled inside)... just to open the green box or does it have some 'calibration/setting' function?

SDsolar
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Michel Keijzers
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    Tuning , that's why its covered with gunge to stop you fiddling with it. – JIm Dearden Jul 22 '17 at 12:22
  • Ok, than I might have a problem with one, because it was really easy to change :-( – Michel Keijzers Jul 22 '17 at 12:24
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    Here is the datasheet: http://radiolux.com.ua/files/pdf/RFmodule.pdf and the search I used to find it: https://www.google.com/search?q=XY-MK-5V – SDsolar Jul 23 '17 at 05:33
  • @SDsolar thanks ... not like a 'normal' datasheet but enough useful information – Michel Keijzers Jul 23 '17 at 11:05
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    Yeah, @Michael, I agree on both points. That's why I included the search itself so perhaps you can find something that this one might lack. But at a glance, it looked like it had what you wanted to know. – SDsolar Jul 24 '17 at 03:20
  • @SDSolar I didn't found that one (didn't look further), actually my first look included datasheet and it didn't find it, so thanks! – Michel Keijzers Jul 24 '17 at 08:43
  • It does not look like an authoritative data sheet to me. It specifies 25cm antenna for the transmitter and 32cm antenna for the receiver. I don't think either of those relate to 433MHz wavelength. – Douglas Held Jan 11 '22 at 15:53

2 Answers2

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The component in question is called a variable or tunable inductor. The screw slot is in a ferrite material that cams in or out of the coil form as it is turned. The inductance varies according to the position of the slug relative to the coil.

The reddish, clear material on top of the coil form is a sealing compound to keep the ferrite material from moving after it was properly adjusted.

The tunable inductor, along with a capacitor, make up a resonant circuit. By varying the value of the inductor, the resonant frequency is adjusted. In this case, it likely sets the receive frequency.

Edit to get it tuned back on frequency:

Just move it a bit away from the transmitter and adjust the slug until you start receiving. Find the middle position of your turning where it receives. Then move it further away and adjust again slightly. Keep doing this. Each time you will notice that it gets more touchy to adjust to the center of the adjustment. Stop when you cannot improve it with slight nudges. You are then back on frequency.

To help you see how much you are turning your "twiddle stick" (which should be non metallic) put a small piece of tape on the shaft and let it stick out like a flag on a staff.

Glenn W9IQ
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  • Thanks ... in that case I ruined it (or at least, changed the frequency of one of them).... luckily I have 4 left :-) – Michel Keijzers Jul 22 '17 at 14:48
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    See my addition to the answer to tune it back up. – Glenn W9IQ Jul 22 '17 at 15:29
  • Thank you for that remark ... I will try to do that ... but it seems quite some work .. since I have 4 others, I will use those 'first' :-) But good to know it can be fixed – Michel Keijzers Jul 22 '17 at 15:49
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    At 433 MHz, the screw is likely not ferrite, but metallic (brass?). Your caution regarding non-metallic adjusting tool certainly applies in any case. – glen_geek Jul 22 '17 at 17:20
  • I have used filed-down wooden chopsticks for things like this in a pinch, if it is easy to change. – SDsolar Jul 23 '17 at 05:36
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If you have the transmitter for those receiver boards and you (preferably) have an O'scope to observe, you could re-tune the inductor to receive the signal again. Otherwise....don't touch that! :)

To learn a little more about the board I found this on youtube: https://www.youtube.com/watch?v=RHJVyMYJ1XQ

TurtleWax
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  • Thanks ... I will take a look at it (good to know it's not broken). And yes, I have an oscilloscope, although it's really hard to handle (very old one) – Michel Keijzers Jul 22 '17 at 15:50
  • If not the O-scope then perhaps use one of the other good receivers to tune the transmitter for most reliable signal. – SDsolar Jul 23 '17 at 05:35