URGENT HELP NEEDED !!!!! RF TRANSCEIVER PROBLEM !!

[ayoubw]

hello there ..

I've purchased two RF transceiver modules, their datasheet is on this site:
**broken link removed**

the transceivers can work in both address & broadcast moe, broadcast mode requires address learning through pressing the learn button.. for more info plzz look on the Device Datasheet, and the "RS232 connection to host PC" design.

1. Pressing & releasing the learn button in addressed mode for both modules in turn would NOT make both modules start to flash(flashing indicates address learning), while pressing each module separately for 10 seconds DOES drive the modules to erase mode(as noted in the datasheet). i.e. the modules can read each other's signal!

2. I'm a new newbie in radio communication, but when I asked a technician for help, and we used RF Oscilloscope to check for radio transmission. On pressing each RF module learn button, a spike was noticed to appear on the oscilloscope for a second: meaning there IS transmission of a radio signal, no other spike appears later on, and the other RF module still doesn't seem to read this Radio Transmission.

3. I've connected the modules to the serial port, using a straight serial cable configuration, but still no communication is establish neither in Addressed nor in Broadcast Mode.

thanking you for help in advance,
cheeerz,
AYOUB

 

[House_Cat]

Did you build your own circuit with these modules, or did you buy the evaluation card?

If you built your own circuit, it would help to see the schematic. There are several pins that need to be held high or low to set initial conditions, channel, mode, etc. The data sheets are fairly clear. If you could tell us what the circuit connected to the modules looks like, we might be able to figure out what is going wrong.

 

[ayoubw]

hello house_cat,

thanx for your reply, and heere i attach the schematic i'm using.. it's the TRXQ1 application schematic: RS232 connection to host PC... and yes .. i wired my board, didn't use any developement kits ..

if more information is required .. plz let me know !! it's a bit urgent !

cheerz
AYOUB[/img]

 

[House_Cat]

Have you checked the steady state voltages on the module with a voltmeter to make sure that each pin is really biased as intended - particularly pins 12, 15, 16, and 3?

What sort of antenna are you using on pin 2?

I know you are in a rush, but I'm trying to do the troubleshooting in words as I would physically if the circuit were here in front of me.

 

[ayoubw]

hi house_cat,
i thank you very much for your co-operation,

okaay .. yes i checked the voltages on those pins, and is as required, the antenna i'm using is a normal straight wire of length 15.5 cm, i was suspecting this might be the problem, but when we checked the RF oscilloscope it was transmitting without getting replies back! anyways the RF modules are not even communicating within short distances !

i'm suspecting one thing ..
this module can work in addressed mode and broadcast mode, if the module doesn't have a serial number burnt into the device eprom at manufacture time, it will have to function in broadcast mode.. this is one thing ..

other thing .. i need to check what type of cable that must be connected between hybrid, and the host PC ? it must be a straight cable.. right ? Tx - Tx, Rx - Rx, RTS -RTS & CTS- CTS .. isn't that true? and what about the rest of the pins ?

i checked using a logic analyzer the pins on the module, the CTS state is always '0' meaning CLEAR TO SEND, and the RTS is always '1' meaning no requests to send!

i hope that this helps .. thanking you again for co-operation ..

cheerz,
AYOUB

 

[House_Cat]

Yes, your cable can be straight through. The schematic shown in the module data sheet takes care of the crossover to make sure the data is on the right lines according to the description given for the signal definitions. The only thing I normally do on connectors to devices like this is short DSR to DTR (data set ready - data terminal ready). Your RF modem doesn't provide a DSR signal. The software can then be set to hardware handshake.

The one thing I noticed about the data sheet schematic is it shows a short between RXD and RTS (sloppy schematic drawing). In reality, RXD should only go to pin 8 of the MAX222 and RTS should only go to pin 9 of the MAX222.

Reading the data sheets, I can't see anything else that can be stopping you at this point. If the circuit is properly built like the schematic (minus the error noted above), and you've followed the procedure on page 8 of the data sheet, and the modules still don't properly respond - there must be a problem with one or both modules.

 

[ayoubw]

hi there,

thanx for the advices ..

here are some new things that happened:
I re-wired the modules again, and checked the straight cable, the result was:
The modules can run the addressed mode test: if the two modules are placed close to each other, by clicking the learn button for both modules, both leds start to blink for few seconds.. meaning that the modules are address-learning each others address.

now the problems that i'm facing are:
1. the modules only address-learn each others address when placed withing 5cm distance, and without using antennas!! i tried using an antenna i purchaced for both modules, but on connecting them, addressed mode doesn't work anymore!! i tried to move the hybrids further appart... no response .. and i tried to increase antenna length, also no response .. i was advised to use a 10pF capacitor before the connecting the antenna to the antenna pin in the RF module, but also no reponse ...

2. i wrote a visual basic program that uses the hardware handshaking, hence try sending characters to the RF modules. the result i'm getting that each time i try sending sth, i receive 'F' character back .. meaning Failure .. this is a good indication that the connections and the software are running correctly, but there's sth wrong on the transmission.

what can be done in this case?

thanx again for co-operation

cheerz,
AYOUB

 

[House_Cat]

When you put the antenna on each module, make sure that the antenna is clear of all other objects - especially at the tip.

When the antennas are mounted, you will probably need to separate the modules by a couple of feet. It may be that the receiver front end is being swamped by too strong a signal when the modules are close together with the antenna gain you will get. Be sure that the antenna is the proper length for the frequency your are using or you will reflect energy back into the transmitter module rather than radiating it.

You really shouldn't operate the modules without antennas for any length of time - you could burn out the transmitter final amplifier running it unloaded.

 

[ayoubw]

Hi there,

1. Happy New Year Everyone
2. I thought sending the pics of the hybrid will help figuring out the prolem!! Thanx..

cheerz,
Ayoub

 

[House_Cat]

One additional thought - you have your units hardwired for 9600bps (baud). Make sure your PC end is set for 9600bps with 8-data, no parity, and 1-stop (this comes from the RF600T datasheet). If the data rate and byte structure isn't matched, you won't get sustained communication between the PC and the module.

 

[MACRF]

it's look like module from telcontrolli.com RXQ 1 based on NORDIC nRF401 .