The receiver is not DC coupled, and very likely has
a data slicer that has a time constant you are exceeding.

It might help knowing how these things work. These receivers
are typically used in automotive RKE type applications. The transmitters
are OOK (AM). The receiver "decides" between a "on" and "off" by
looking at the average TX level and dividing by two. This 1/2 sig level
is feed to one side of a comparator, the other side gets the signal.

Most RKE applications don't use on/off directly for the 1's and 0's. They
use PWM modulation where the width of the pulse determines if the
data is a 1 or 0. Sometimes manchester coding is used. The point being, with
PWM, with a AVERAGE of 50/50 duty cycle,  you can use a AC coupled
signal as the slicer has a chance to  get a good 1/2 sig decision level.

So this would explain with a long transmission you LED eventually goes
off as the data slicer decision level keeps rising.

Good luck

Jeff


German wrote:

> The receiver is correctly showing me the pulses through
> the led but after that digital output goes high for about a second or
> more turning the led on and then dims slowly to a LOW digital level
> (which should be the correct behaviour after the pulses.)
> The linear output doesn't seem to show this peak but I'm not sure
> 'cause I don't have suitable equipment to measure it.
> Receiver can be tuned manually.
>
> Any ideas or advice to solve this are welcome.
> Yes, I know, I have no idea about RF or ascii art ;)
>
> Bye.
> ------------------------------------
> netQ <netquake@innocent.com>
> http://virtuaweb.com/picprog
> "Home of amateur PIC programmers..."
>
> -----BEGIN PGP PUBLIC KEY BLOCK-----
> Version: 2.6.2
>
> mQCNAzV38BkAAAEEALfWv9j3f+tZ+z2IW+2o9Ebx4bUGnHjHPqIe0a6yVKawaeV/
> Y4I6L2/A0ddbVMG8+qJ0MvHNkr3DzYkpW+hTl9zAzXkKBdZ3GA5bbvot7entl/O2
> YDtRWUV730koxBo5iFFUbJH5kbmkox+h3znj34zPnZNWzNaqOAwol3wABfBNAAUT
> tBxOZXRRIDxuZXRxdWFrZUBpbm5vY2VudC5jb20+
> =0bVU
> -----END PGP PUBLIC KEY BLOCK-----