Can you spot a transmitter in this device? Can I add an antenna to this device?

Thread Starter

Denis Molodtsov

Joined Jun 2, 2021
7
I have puchaed a wireless Bike Alarm and wanted to figure out how to extend its range. I want to try to extend its reach to 50 meters from the default 20 meters.

There is wireless "fob" (KS-WL09C) that I disassembled. The photo is available below. Question: Can someone, please, spot a transmitter on the photo? If I know where it is, perhaps, I can add an antenna to extend its range.

I was trying to search the schematics online, but could not find anything. I was also trying to google the names of the element IDs that are imprinted on them, but didn't find anything either. The device also has something written in Chenese that might be useful, but I can't read it.

Context: I am a beginner, but know some basics and I know how to solder.

1622658161893.png


There are 4 buttons:
- On button
- Off button
- PA button
- CH button

1622658185293.png
 
Last edited:

Thread Starter

Denis Molodtsov

Joined Jun 2, 2021
7
I discovered some more information. I think, it's LR433T2 responsible for transmitting the signal with 433 MHz.

1622660693391.png
1622660920411.png

LR433T2 seems to have 3 pins. This is how it looks upside-down:
1622660726275.png

I am thinking of adding a 433MHz antenna to the middle pin. Do you think that will work?
1622660682001.png
 

Attachments

BobTPH

Joined Jun 5, 2013
3,308
That part would appear to be a 433 MHz crystal, though 3 pins is not the usual number. Perhaps the 3rd one is connected to the case?

I don't think adding an antenna to the crystal will do anything except likely kill the oscillations.

There must already be an antenna. Is there something built into the case that is contacting some point on the PCB? I am thinking that little metal loop near the top of the second picture might be a contact for an antenna,.

Bob
 

Delta Prime

Joined Nov 15, 2019
996
Hello there,welcome to AAC!
:) I concur with Mr. @BobTPH
You can open up the alarm if you like and you probably find exact biodirectional Surface Acoustic Wave filter (SAW)

photostudio_1622663730395.png
 

Thread Starter

Denis Molodtsov

Joined Jun 2, 2021
7
Perhaps the 3rd one is connected to the case?
The PCB is enclosed in an insulated rubber "sleeve". This sleeve is enclosed in a plastic case with no connectors to anything and any metal whatsoever. The board does not touch the case directly. I've checked carefully and it does not seem there are any antennas in the case.

I don't think adding an antenna to the crystal will do anything except likely kill the oscillations.
I see. Then I won't attempt it. Maybe I can figure out if the manufacturer even included a place for an antenna in the first place. I'm afraid they didn't anticipate it.

I am thinking that little metal loop near the top of the second picture might be a contact for an antenna,.
Which metal loop do you think it is? I've added numbers and a mirror image of the flip side:
2021-06-02_17-12-06.jpg
 

Yaakov

Joined Jan 27, 2019
3,153
There is going to be an antenna integrated on the PCB. The white solder mask makes it impossible to see the traces, but in any case small transmitters like that are very sensitive to impedance of the antenna and you are likely to make things worse, not better.
 

Thread Starter

Denis Molodtsov

Joined Jun 2, 2021
7
Hello there,welcome to AAC!
:)I concur with Mr. @BobTPH
You can open up the alarm if you like and you probably find exact biodirectional Surface Acoustic Wave filter (SAW)
Thank you! Do you think, the arrow on your picture is the place for the antenna I should use?

I have opened up the alarm and I found these elements:


2021-06-02_18-08-11.jpg

If I know the SAW used, is it useful? For example, maybe I can order a long-ranged device that is compatible with it? Or maybe I can build something from scratch? I am just looking for the simplest option. I don't mind buying something that will help me increase the range.
 

sagor

Joined Mar 10, 2019
439
I look at that small trace between ON and OFF, passing around PA and CH. That looks a bit like a loop antenna to me. Might be wrong, but my guess, else why the long loop?
But, is that an actual trace or a shadow of some plastic cover? Hard to tell from the pictures. Only physical inspection would tell...
 

Thread Starter

Denis Molodtsov

Joined Jun 2, 2021
7
I look at that small trace between ON and OFF, passing around PA and CH. That looks a bit like a loop antenna to me. Might be wrong, but my guess, else why the long loop?
But, is that an actual trace or a shadow of some plastic cover? Hard to tell from the pictures. Only physical inspection would tell...
I've placed the board on top of a bright LED and I can see this. The right image is mirrored. On the left picture, the large dark loop at the 1/3 part of the image looks like an antenna. Am I right?
LED image.jpg

I wonder If I can use the loop hole #1 or #2 to add an antenna?

1622674017834.png
 

Delta Prime

Joined Nov 15, 2019
996
Hello there again
I was never good at playing "Where's Waldo" :p You don't have to take a photo flip the cover over do you see a square peice foil or copper?
 

Delta Prime

Joined Nov 15, 2019
996
The PCB is enclosed in an insulated rubber "sleeve". This sleeve is enclosed in a plastic case with no connectors to anything and any metal whatsoever. The board does not touch the case directly. I've checked carefully and it does not seem there are any antennas in the case
My apologies it's strike three for me default for not reading. Good luck to you
 

Thread Starter

Denis Molodtsov

Joined Jun 2, 2021
7
Thank you everyone for helping me!

I have ordered an RF Wideband Amplifier and I am going to attemp to connect it to the loop holes #1 and #2. These holes seem to be connected to the antenna. Of course, I might mess things up, but I am willing to give it a try. Worst canse, I'll learn something new.
1622676733739.png

1622676827941.png
 

DickCappels

Joined Aug 21, 2008
7,426
This transmitter was not intended to drive an external antenna or amplifier. L1 in post #1 which is the top half of the photo in post #14 is the antenna. Unless you are very good at tweaking amplifiers to work with RF sources with unknown impedances you won't be able to do much with this. The positive aspect is that although it will difficult for you to increase the intensity of the RF filed, at least the frequency will be stable because of the SAW resonator on the base circuit is very stable.
 

seanstevens

Joined Sep 22, 2009
78
Post #14 the inductor & antenna combined is almost at 1 all the way to 2. The inductor/antenna combo. The power of this kind of circuits is very very low, in the order of a few microwatts. I would imagine if you connect anything to the loop the oscillation will probably stop altogether as you will unbalance it, as its already been pointed out. Also, I doubt it the device has enough power to even drive your RF amp. A MAR RF amplifier device may just be sensitive enough to amplify it but you still have to match the output to its input and have the MAR on the same PCB as your device. Not easy.
 

Thread Starter

Denis Molodtsov

Joined Jun 2, 2021
7
The tab on the top of the transistor is the collector. You can try this. However, read post #15 by @DickCappels .
Thank you! Sounds like a good idea. I am going to try the transistor's collector. I am now waiting for the RF Wideband Amplifier to arrive. I will update the thread with the results.
 
Top