RF 433mhz. Missing antenna? (lots of junk receiving)

Projects General Guidance
1

Hi All,

I got (as many others) a set of RF 433 TX/RX from ebay. Exactly like:

XY-MK-5V and FS1000A (XY-FST)

While connecting it, i'm picking up lots of noise/junk on the receiving end (continuously).

My questions are the following:

  1. On both units there are no external antenna's, does this mean there missing?
  2. I see on both a small hole with 'ANT", assuming i need to attach my own antenna? Do the TX/RX need both one?
  3. I was assuming that the small tiny copper wire (spiral), were the antennas, but maybe i'm wrong?

Many thanks!

36R

2

Looks like they are intended to have an antenna. I think a straight piece of bare wire 17.3cm long would be appropriate.

3

I am not surprised you are receiving garbage.
Your code will have to ignore garbage and look for valid data.

4

@LarryD, Well i expect to have to filter some junk. But this seems something else, its only (99.9%) junk and some times i see a part of my message.

5

Garbage data is normal for those cheap ASK receivers.
They have no squelch, so in the absence of any signals they simply output broadband noise.
Your receiving code has to identify the valid signals whilst ignoring the junk.

6

Look at the virtual wire lib in the playground.

Mark

7

mauried:
They have no squelch, so in the absence of any signals they simply output broadband noise.

I suspect it's worse than that.

I am pretty sure these devices are in fact, superregenerative receivers - apparently with an RF stage preceding, which would explain why my/ your car remote door lock works nowhere near as well in a car park (surrounded by other cars - containing these receivers) as it does out "in the open".

8

There are 2 types , normal superhets and super regenns.
Its hard to tell from looking at them which they are , but yes, the super regens do radiate quite a bit and can interfere
with other receivers in the vicinity.

9
  1. On both units there are no external antenna's, does this mean there missing?
  2. I see on both a small hole with 'ANT", assuming i need to attach my own antenna? Do the TX/RX need both one?
  3. I was assuming that the small tiny copper wire (spiral), were the antennas, but maybe i'm wrong?

The external antenna is not included. That small hole is exactly where you connect your external antenna. You can send and receive some data without antennae, but your range will be very limited. Putting an antenna on only the TX or RX will greatly extend your range, but putting one on each will extend it even farther. The tiny copper wire (spiral) on the unit is an inductor, not an antenna.

From the link you supplied:

2.Great influence on the antenna module reception, preferably connected to the 1/4 wavelength of the antenna, typically 50 ohm single conductor, the length of the antenna 433M of about 17cm;

The way to calculate the antenna length is to divide the speed of light by the frequency to calculate the wavelength, and divide that by 4 to get a quarter length. That comes out to about 17.3 cm or 6.8 inches. Just cut a piece of wire 6.8 inches long and solder it into that hole, on each module. If that doesn't give you better range, you can mess with ground planes and such, but in my experience just putting the wires on there makes the biggest difference.

While connecting it, i'm picking up lots of noise/junk on the receiving end (continuously).

That's normal for this unit. If the receiver doesn't pick up any transmission, it gradually increases the sensitivity until it DOES pick up something. If you're not transmitting anything, that will be just random noise. The solution is to transmit more than one bit at a time, and have some sort of pattern so the receiver can tell the difference between noise and real data. Also, you have to send some sort of pre-header so the receiver can adjust the sensitivity when it starts getting real data. I recommend using the VirtualWire library, which does all that for you.

10

mauried:
There are 2 types , normal superhets and super regenns.
Its hard to tell from looking at them which they are

Not hard at all.

The thing in front of me has exactly three inductors, all open (and in three different formats), no IF cans or resonators and two transistors between them.

Not to put too fine a point on it, Chinese manufacture and all, but you don't get a decent superhet this cheap.

Or just maybe - a fremodyne!

What bugs me, is why they would use something so cheap and dirty in a car, but the behaviour of the remote controls does suggest they do.

11

Hello,

Sorry to reopen an old post but I've got the exact same problem.

I'm writing a sketch to record and replay RF 433Mhz signal from electrical plug remote.

My sketch starts in the setup by waiting for a signal over a defined threshold (let's say waiting for "data"), then it lights up a LED, records the high and lows duration for 500 times, turns of the LED and reports that on the serial monitor.

I've done that beginning of the week, sitting in my living room in front of my TV powerred up, and it worked like a charm : starting the sketch, the LED stood off and after some seconds or more, I had to put my original remote 2cm from the RX module and press a button to see the LED light up, and after half of a second turned off and saw my signal on the monitor.

That was perfect, every evening.

Until yesterday, first bank holiday day, the receiver gets lots of junk and garbage, each time I reset it.

So I went your direction, started to press the original remote button before resetting my sketch, and then yeah, it got my signal. That means that as you said, with my signal being stronger, it adjusted itself and got only my own signal.

The question is : why the hell does my RX module get all the garbage since yesterday, knowing that the whole week it didn't get anything ?? And knowing that it does not receive my own signal if my remote is more than 3cm away from the RX module, so how can it get this garbage coming from elsewere ?

Can I suspect one of my neighbours to have turned on an equipment emitting permanently some very strong signal ? (I live in a flat)