Signal Received Only When Transmitter is Probed - RF Cafe Forums
Post subject: Signal received only when transmitter is
Unread postPosted: Fri Oct 15, 2004 7:40 pm
am using a Melexis transmitter (72031 - 915 MHz, FSK) in a remote
sensing device. The problem I have encountered is that the receiver
will not receive the signal (so I assume the transmitter is not
transmitting) unless a wire of some sort is placed on the ROI pin
of the transmitter. This wire need not be grounded and has to be
a couple inches long for the 'wire fix' to work. I found this 'solution'
while using the o-scope on that pin. My only experience with RF
comes from the LINX line of transmitters and receivers so designing
with a non-'Plug-n-Play' device is giving me some problems.
Could this be a ground loop problem or is it something more
complicated. Any advice would be greatly appreciated.
Unread postPosted: Sat Oct 16, 2004 10:18 am
Joined: Sun Aug
03, 2003 2:02 pm
Location: Erie, PA
Without knowing what your baseline configuration is,
it will be difficult to provide much help. The wire on the ROI pin
causing the Tx to work could be due to many things from a bad solder
joint to a faulty crystal or other component. Even the IC could
be damaged from ESD. Could you please take a look at the couple
questions below to provide a little more insight into your situation
to others and me?
I took a quick look around the Melexis
website and found that they offer a demo board for the TH72031.
http://www.melexis.com/prodmain.asp_Q_c ... E_EVB72031
that what you are using for experimentation? If not, does your PCB
layout generally follow the outline given on page 8 of the user's
guide that comes with it?
You have probably already seen these, but there is a page on
the Melexis website with application notes.
Here is the datasheet for the part if anyone else cares to offer
What are you using for a receiver? If it is one of the Melexis
devices, are you using the recommended PCB layout for it?
Finally, do you have aspectrum analyzer available for troubleshooting?
Kirt Blattenberger :smt024
Tue Oct 19, 2004 2:35 pm
For the transmitter I am using
the circuit shown on the Melexis data sheet for the EVB with the
same values for all components although the physical layout is quite
different to fit on my PCB. On the receiver side I am using the
Melexis EVB (TH71111) just to ensure the transmitter is operating
As far as the spectrum analyzer goes, I don't access
Thanks for the reply,
Post subject: Problem Resolved
Wed Oct 20, 2004 3:36 pm
For anyone interested...
The problem was indeed a simple one. The 'wire fix' was simply
adding a certain amount of capacitance to the circuit and thus tuning
the frequency to a value within the bandwidth of the receiver. In
the end, with a little trial and error, it took changing a few capacitors
to different values (quite different from the data sheets) and now,
all is well.