Page 1 of 1

Signal not received when receiver too close to transmitting device?

Posted: Wed Apr 07, 2021 1:44 pm
by YellowJacket
Hello,

Total newbie here

I'm using the RTL-SDR Blog v3 dongle to decode the signal of the old Honeywell 5800 door / window sensors that the previous owners left in my house. The Honeywell sensors transmit on 344.975MHz. I use RTL_433 to decode the signal, and I have the sample rate set to 1000k.

Everything works great except that it never receives the signal of the sensors that are closest to the receiver. When I move the receiver around the house, it starts to "ignore" other sensors close to the new position.

It appears that it does not receive signals when they are "too strong"? Does anyone know why this happens and what can be done to mitigate the issue?

Thank you for your help!

Re: Signal not received when receiver too close to transmitting device?

Posted: Wed Apr 07, 2021 4:57 pm
by Stromeko
YellowJacket wrote:
Wed Apr 07, 2021 1:44 pm
It appears that it does not receive signals when they are "too strong"? Does anyone know why this happens and what can be done to mitigate the issue?
Yes, if you overload the RF frontend you will not be able to pick out and decode the signal.

I would start off with switching the AGC off, it works against you with intermittent signal since it will crank up the gain to the max when no signal is received, then can not dial it back fast enough when you get a new reading from the sensor. Try to find the gain setting that makes the farthest sensor drop out, then go up until the nearest sensor stops getting read correctly. Set it somewhere in between and check if you notice a higher error rate from the farthest/nearest sensors over a longer time span (a day at least) and adjust one or two notches up / down accordingly.

Re: Signal not received when receiver too close to transmitting device?

Posted: Wed Apr 07, 2021 10:14 pm
by YellowJacket
Thank you very much! I'll give that a try this evening