network matching for RF module FXTH87

[sunrme]

Hello,

I’m working with FXTH871511 and now I'm testing RF module. So I have a problem, because it works not so well like others analogs.

I’m not a professional in RF and don’t know much in this orea, so if any of my thoughts are not right please correct me.

So, I found two solutions for network matching in documents.

     1)      From KIT. This scheme for 434 MHz (from here) :

I remove extra components like DNP or 0 Ohm, and get scheme like on right side. In this case RF module work but I think only for 30% of opportunities (I check the distance from transmitter and receiver).

     2)      Second scheme I also get from the same file:

RF transmitting does not work. Because need to pull up L2 to VDD (like in datasheet)

Also need add capacitance between RF and GND (FXTH87EDRM: a parasitic capacitance of 3 pF is added between the RF out and ground to reach the device output impedance.)

So we get scheme like this:

Now, the transmitter works but I think for 70% of max optimal values.

So, please help me to choose right solution and how I can improve it to get better work for RF module.

[davidramirez]

Hi.

What is your RF receiver because i try transmitt to rf but don't work.

[sunrme]

Hi all!

I made conclusions on this subject

1. For these sensors, freescale (NXP) does not have a typical network matching scheme (all are listed in the datasheets have errors or a very weak signal).
2. To make network matching scheme, need a strong team that will work only with RF transmission. And if one is not present, then:
3. It is necessary to use an external chip transmitter for good transmission. In this case there is no sense to use this sensors and better use from other company without included RF module to reduce the cost.

[sunrme]

So, actually I didn't find best solution for RF module. I checked out the various options, copied the other solutions like this:

But it isn't work well.

Maybe someone knows what I'm doing right and what is not?

[anthonyduhamel]

Hi Sunrme,

RF domain is a dangerous territory when you're not a specialist. In fact we have full-time engineers working on it at Freescale to improve RF transmission on TPMS modules.

The matching network is not the only way to increase RF efficiency. Transmission range also depends on your PCB design, how you placed components, the used antenna.... It is a meticulous and hard work...

It's a very difficult area, and as I'm not an expert, I can't help you on this side. Maybe you can acquire a TPMS Kit from Freescale to take its inspiration but again, it not RF domain is not easy.

Anthony

[sunrme]

Hi Anthony,

Thanks for your reply. I understand that the rf module is a very difficult thing. But I'm not very demanding, and I just want to get  70-80% of power efficiency for such systems. I naively believe that in this case we can use Pareto rule, that 20% of the work, gives 80% of the results. I am sure there is a small set of rules when designing matching network, which will give an acceptable result.

Well, my question is not primarily how to track or how to get best antenna.  First of all, I need to understand how should look matching network circuit, and how to select components, what is an algorithm for setting RF, how to check impedance or something like this.

In the documentation from freescale I found several options that conflict with each other’s and that's try to understand.

So that’s why I’m here. Maybe your colleagues throw some light on this problem.