433Mhz Garage Remote booster mod

[hgg]

Hi,

I would like to increase the range of my garage door remote.
I bought a 4 channel programmable remote, a 30db wide band RF booster and a 433Mhz antenna.



The problem is that I cannot find where the antenna is connected on the PCB of the remote.
It looks like that there is no PCB trace antenna as well.  Here is the PCB.  The back side is mirrored,
so that the traces are aligned.



and the amplifier :



Is there any point on the circuit above that an external antenna might be connected?
Thanks!

[joao2004]

Try at the collector of Q1...

check datasheet of LR433T2

[hgg]

In the LR433T2 datasheet I found, it shows it as a two pin device,
while the one on the board all three pins are connected.
Its a three pin and the middle is ground.

The collector of Q1 is connected  to L0 on left, correct ?
L0 and C7 are not populated though.

[MagicSmoker]

It looks like the antenna is the thicker trace on the bottom of the board connected to C1 by 2 vias and terminating at the unpopulated L0.

I'm not going to play EMC police, but note that the ISM band (433MHz) is very popular for baby monitors, garage door openers and other remotes, etc., so boosting the output of your transmitter may incur the wrath of your neighbors and/or the Greek equivalent of the FCC.

[hgg]

I'm not going to play EMC police, but note that the ISM band (433MHz) is very popular for baby monitors, garage door openers and other remotes, etc., so boosting the output of your transmitter may incur the wrath of your neighbors and/or the Greek equivalent of the FCC.

About the FCC.  Where I live we have a continuous transmission on 425Mhz at -15db (!) of I do not know what.
I discovered it by accident when I was building a high frequency led dimmer.  Also when I was playing with some
433Mhz receiver switches they were triggering by themselves all the time and I gave up on the project...



The baby monitors should be on fire by now.  :-)  I don't think that with that short burst I will interfere with any
other garage doors.   If I succeed I will check the range and see if I can tame it down.  I just need about 50m range.
Now you have to be next to the garage in order to open it...

The thick trace from C1 has a length of 35mm.  Is this correct for a 433Mhz transmission?
Why at the end of the antenna there is a place for an inductor and a capacitor?  The inductor also is connected
to the collector of Q2.  Wouldn't this defeat the purpose of the trace as an antenna?

[MagicSmoker]

About the FCC.  Where I live we have a continuous transmission on 425Mhz at -15db (!) of I do not know what.

Like I said, it's a popular frequency band...

The thick trace from C1 has a length of 35mm.  Is this correct for a 433Mhz transmission?
Why at the end of the antenna there is a place for an inductor and a capacitor?  The inductor also is connected
to the collector of Q2.  Wouldn't this defeat the purpose of the trace as an antenna?

No, it isn't close to the right length, but that is done on purpose to limit the ERP ("effective radiated power"). As for the (unpopulated) LC network connected to Q2 at the end, I have no idea what that might be. I have seen a series LC network added to the end of an intentionally short antenna such as this to act as a harmonic trap and improve the VSWR some, but that doesn't seem to be the case here.

[hgg]

Its not only the LC network.  The end of that trace (which is connected to LC) is also connected
to the collector of Q2.  I've double checked with the multimeter.

[edavid]

Have you thought about adding the antenna and/or amp to the receiver instead of the transmitter?  You might need a bandpass filter as well.

Or, how about buying a full size remote with a 12V battery?  That will probably have more output than your keychain remote.

[hgg]

The first thing I did was to connect an antenna to the receiver but the difference was small.
I think that the problem also has to do with the constant -15db 425Mhz transmission.
The constant -15db "noise"  is huge in comparison with the remote power output.

I have the original remote which has a slightly better range but it is bulkier so I have to find a way
to amplify my transmission signal.

[macboy]

Defeating interference by throwing MOAR POWER at the situation isn't usually productive. Why not just move to another free-usage ISM band?  Depending on country, 868 MHz, 915 MHz, 315 MHz, 2.4 GHz, etc.
Any transmitter/receiver pair that has can activate a relay can be used to trigger your door opener.

[hgg]

This is the daughter board of my door opener :
https://www.aurelwireless.com/wp-content/uploads/user-manual/650201110G_um.pdf

I am not sure that I will be able to source a similar module with a different frequency.

[hgg]

Is it possible that the transmission happens directly from the lr433t2 resonator
and the circuit has no antenna at all?

Based on the manual of the LR433T2 resonator, I think that the implemented circuit
is the first of the two examples :



If this is true, the I should be able to connect antenna to the capacitor C.
The problem is that both the inductor and the capacitor are missing and the inductor
has been shorted with an actual trace.

Would it be possible to cut the trace and solder an inductor and a capacitor in order to
connect the antenna?  Is so, how do I choose the values?
C7 is going to ground, so it would have been a bypass capacitor.   

Any RF guru ? 

[MagicSmoker]

No, this part is a SAW resonator, which behaves much like a crystal so needs gain to oscillate.

You might want to check out this datasheet for a competing part that has a wealth of information in it on how to design these sorts of things:

https://www.linxtechnologies.com/wp/wp-content/uploads/txm-fff-lr.pdf

[edavid]

The first thing I did was to connect an antenna to the receiver but the difference was small.
I think that the problem also has to do with the constant -15db 425Mhz transmission.
The constant -15db "noise"  is huge in comparison with the remote power output.

I think I would try to find that source.  It must be very close to your garage to be so strong.

Or, build a notch filter.

[hgg]

A notch filter for the antenna on the receiver you mean?
This has to be an extremely narrow filter in order to do anything.



6km from my house and the transmission is the same and on the same frequency!

I have a suspicion that this might be a carrier for the TETRA system.
https://en.wikipedia.org/wiki/Terrestrial_Trunked_Radio#Technical_details

They can transmit on "For civil systems in Europe the frequency bands 410-430 MHz"
https://www.electronics-notes.com/articles/connectivity/private-land-mobile-radio-pmr-lmr/tetra-radio-interface-frequencies-bands.php

I think the police is using it.  But why the constant transmission ?  Is that how it works?
If that is the case, connecting a high amplification on the remote might not be the best idea...

I read that it is not so healthy as well...
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5010210/

Is there an FCC for the FCC ?...

[johnkenyon]

Defeating interference by throwing MOAR POWER at the situation isn't usually productive. Why not just move to another free-usage ISM band?  Depending on country, 868 MHz, 915 MHz, 315 MHz, 2.4 GHz, etc.
Any transmitter/receiver pair that has can activate a relay can be used to trigger your door opener.

Why not improve the signal to noise ratio by moving the receiver closer to wherever you want to operate it, or installing an external antenna.
Both of these are less of a faff than playing with RF amplifiers...

[hgg]

Try at the collector of Q1...

The circuit is designed to use the inductor as an antenna, but this worked perfectly, thanks!
Huge increase in signal power.  I can now make a compact unit that will reside permanently
in the car.

"Why not improve the signal to noise ratio by moving the receiver closer to wherever you want to operate it"
I will do that as well because the receiver module is behind the metal door.

Thanks!

[edavid]

A notch filter for the antenna on the receiver you mean?
This has to be an extremely narrow filter in order to do anything.

That's why you would be better off with a notch filter rather than a highpass.

6km from my house and the transmission is the same and on the same frequency!

I don't see how that's physically possible.  It strongly suggests that the 415MHz signal is an artifact of your equipment.

Is there an FCC for the FCC ?...

Why are you talking about the FCC if you are in Greece 

[hgg]

Did you see the video I posted?
Two different instruments show the same signal.
Seeing the signal on the spectrum analyzer and at the same time listening on the UHF radio.
Just checked with another radio.  There is nothing wrong with the equipment.

>> Why are you talking about the FCC if you are in Greece 
You know what I mean...  The corresponding European agency.  BEREC, CENELEC etc.

[edavid]

Did you see the video I posted?
Two different instruments show the same signal.
Seeing the signal on the spectrum analyzer and at the same time listening on the UHF radio.
Just checked with another radio.  There is nothing wrong with the equipment.

Back to the notch filter idea then

>> Why are you talking about the FCC if you are in Greece 
You know what I mean...  The corresponding European agency.  BEREC, CENELEC etc.

I actually didn't know, but OK.

[hgg]

The solution for me was to build a 433Mhz tuned receiving antenna with ground plane and place it high from the ground.
Now I can open the door from hundreds of meters way. Literally.