I am working on an RF system using 433MHz transmitter and receiver along with HT12E and HT12D. I have make this circuit with this RF pair ( https://www.circuitspecialists.com/stpa-418h-b.html ) and it works fine. Most of the time the RF transmitter and HT12E are not powered to save battery life. I turn them on with my Arduino Pro Mini, then I use a relay to remove D9 (pin 11) from ground. On the RF receiver side the RF Receiver and HT12D are alway on. When I hook up an led to D9 it doesn't light up when the RF transmitter and HT12E are not powered on (which is what I want). When the RF transmitter and HT12E are powered on and D9 is removed from ground the Receiver unit gets the data and through a transistor a relay is activated. Walla, just what I want.
My problem arose when I found out the RF pair listed above are going to be discontinued. So I purchased another pair of 433MHz RFs. ( https://www.ebay.com/itm/4X-433Mhz-...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649 ).
Now with the set up as shown in the attached schematic, the D9 led is always on when there is no signal being sent (even when the RF transmitter and HT12E and NOT powered on. When they are powered on and the D9 led goes off and the whole thing works as it should. But with the D9 source negative (putting out voltage) I can't get things to work the way I want.
Can someone suggest a work around OR look at the two RF pairs and tell me that there is a significant difference between them and I need to get a more compatible (Similar) 433MHz replacement that will work like the old 418MHz pair. Can someone suggest the correct replacement and why (so I can learn).
Thanks for all everyones help.

 

I figured this out. When I was using the 418MHz RF set there were no other RF transmitters in the vicinity. However with the 433MHz set there apparently is another local 433MHz transmitter, because when I set an address on the transmitter and receiver by grounding the A4 pin, the led went out and when I then removed the ground on D9 the led did light up.

 

You need a 330 ohm resistor in series with the led to limit the current otherwise you may damage the RX chip.
I found the same problem with using the 433 Mhz transmitter and receiver. There is something local that uses that frequency regularly and interferes with my received data.