Signal received only when transmitter is probed - RF Cafe Forums
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Post subject: Signal received only when transmitter is probed
Unread postPosted: Fri Oct 15, 2004 7:40 pm
I 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
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?
took a quick look around the Melexis website and found that they offer
a demo board for the TH72031.
Is 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?
you have aspectrum analyzer available for troubleshooting?
Kirt Blattenberger :smt024
Unread postPosted: 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 properly.
as the spectrum analyzer goes, I don't access to one.
for the reply,
Unread postPosted: 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.