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Posts: 2
Registered: ‎09-16-2016

Si4455 frequency selection problem

After some difficulties I've finally got two ZETA-4455 from RF Solutions to talk to each other at 868MHz using a PIC18F44K22 at each end.  However one version of my design has to work at 915MHZ.  So we built some PCBs with the 915MHz versions of the ZETA-4455 modules.  Using WDS I generated a new configuration file with the only difference being a frequency change from 868MHz to 915MHz.  The first message I send is received correctly and a reply is sent back.  However subsequent messages are received correctly but no replies are received.  Power cycling the master PCB means I can now send another message and get a reply but only one.  However if I program the 915MHz modules with the configuration data created for the 868MHZ modules everything works fine at the wrong frequency.

 

Another small issue is that I set the packet length as 20 bytes in WDS and enabled the CRC to be added to the packet however the receive end always reports a packet size of 18 bytes.  This doesn't stop it working, should I add 2 extra bytes onto the packet length to allow for the CRC?

 

An even smaller issue is the WDS preamble length setting, it doesn't seem to correspond to the length seen if a GPIO is set to output the TX data.

Posts: 255
Registered: ‎12-10-2013

Re: Si4455 frequency selection problem

There should be no problem on the function if you only changed the frequency no matter whether the board is designed for 868M matching or 915M matching. Can you please attach your WDS configuration file and generated header file?

Juanyong
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Posts: 2
Registered: ‎09-16-2016

Re: Si4455 frequency selection problem

The problem isn't about getting a ZETA-868MHz module to run at 915MHz or vice versa.

 

I generated two WDS config files one for 868MHz and one for 915MHz, all the other parameters being the same.  With the same PIC control software the ZETA-868MHz module will work reliably at 868MHz.  If I change the include file to the one for 915MHz, reassemble and program a PCB with a ZETA-915MHz module it will not work reliably.  The first message from the master to the slave gets through and a reply is received, subsequent messages are received but no replies are sent.  After power cycling the PCBs, again the first message exchange works but not subsequent ones.  An 868MHz module will not work reliably with the 915MHz software either. 

 

I have come up with a solution.  I use the 868MHz version of the software but select a channel offset of 47MHz (188 x 250KHz) when transmitting and receiving and they now work reliably at 915MHz.