433Mhz key fob tester

Hello,

I need some simply schematics to make tester for 433MHz freq.
No need to read out freq., need just to check if freq present. Can switch one LED for show present freq.
As I wrote in subject, this is for car keyfob testing


wb

Ziko

You can just use a loop of wire for an antenna, a ~ 20 dB gain amplifier chip, and a schottky diode detector with a voltage storage cap at the output. If you push the button and the DC output voltage changes, you have "a signal".

But that does not really test anything. If the frequency is off, the keyfob will not work. If the digital modulation is wrong, the keyfob will not work. If the power is very low, the key fob will not work well. etc etc.

I found RF receiver from used/old car alarm. It has 3pins +5V,GNDand out signal.
When I press button on fob I get ~2.2V from RF out, but when in stendby also voltage variable from 0.2-0.8V and I have LED flashing :(
From signal out I put to 22k to base of NPN and NPN switch LED...


Any sugestion how to fix this dimming of LED whenkeyfob not presed?

wbr

Ziko