RF Transmitter/Reciver

**Luciano** · - 18th February 2008, 13:07

Originally Posted by Fredrick

The maximun output power for the transmitter is 14DBm or 25.11mW
Is that correct?

No.

From ELECTRICAL SPECIFICATIONS/TRANSMITTER SECTION/Output Power:

At 2.1V the power is - 4dBm = 0.398 mW
At 3.0V the power is 0dBm = 1 mW
At 3.6V the power is 4dBm = 2.511 mW

Do not modify the hardware you got from Parallax.
1 mW or 2.5 mW do not make any difference.

**Fredrick** · - 18th February 2008, 13:37

but 1mW and 25mW makes diffrents...
Connect the LADJ to vcc will give +10DB and it´s allowd in sweden.

By the way i have get my code to work now whit inverted mode, idon´t know exaktly what makes it work but i think it have something whit the sync to.

there maybe som other solution to it but this works.

FOR I = 1 TO 3
SEROUT TransmitterPIN,N2400,[$55,$55,$55,63519,Counter,Check]
NEXT I

and yes i sending the code whitout pauses three times i think this helps the transmitter to syncronise.

The Level Adjust (LADJ) line allows the transmitter’s output power to be easily
adjusted for range control, lower power consumption, or to meet legal
requirements. This is done by placing a resistor between VCC and LADJ. The
value of the resistor determines the output power level. When LADJ is connected
to VCC, the output power and current consumption will be at its maximum. Figure
4 on Page 3 shows a graph of the output power vs. LADJ resistance.
This line is very useful during FCC testing to compensate for antenna gain or
other product-specific issues that may cause the output power to exceed legal
limits. A variable resistor can be temporarily used so that the test lab can
precisely adjust the output power to the maximum level allowed by law. The
variable resistor’s value can be noted and a fixed resistor substituted for final
testing. Even in designs where attenuation is not anticipated, it is a good idea to
place a resistor pad connected to LADJ and VCC so that it can be used if needed.
For more sophisticated designs, LADJ can be also controlled by a DAC or digital
potentiometer to allow precise and digitally variable output power control.

Output Power Control Range -80 – +10 dB

**Luciano** · - 18th February 2008, 14:51

From Figure 4:

Diagram Output Power vs. LADJ Resistance:
When LADJ Resistance = 0 then the output power is 9 dBm (7.943mW).

In theory you can get 10mW but then when you read:

The LR Series transmitter is designed to generate 1mW of output power into a
50-ohm single-ended antenna while suppressing harmonics and spurious emissions
to within legal limits.

* * *

In unidirectional links, a good designed transmission protocol will make the difference.
Use redundant data for the purpose of error correction.

**mackrackit** · - 18th February 2008, 15:43

And I will add again.
A good antenna is a must!

**Fredrick** · - 18th February 2008, 22:17

Yes... Now i have get the program to work very well whit inverted mode, tested it at 100 meters and there no errors or missing numbers.

But then we come to the next problem, I have searched the forum and I find out that i´m not alone whit this problem, but the solution for it does´t work for me.

I can´t get the SERIN timeout to work, and yes the input is switching between high and low when the transmitter is off. i have tryed whit an 1K, 3K, 4.7K, 10K resistor between GND and the input pin but when the timeout works the recive module does not and when the reciver work the timeout does not.

So what else can i do? is there an software solution for this or must i use an hardware solution?

**mackrackit** · - 18th February 2008, 23:07

Hi,

Could you post your current code? It may be some thing simple that has been over looked.

**Fredrick** · - 18th February 2008, 23:35

Code:

<html>
<head></head>
<body><!--StartFragment--><pre><code><font color="#008000"><i>'****************************************************************
'*  Name    : Reciver.BAS                                       *
'*  Author  : Fredrick                                          *
'*  Notice  : Copyright (c) 2008                                *
'*          : All Rights Reserved                               *
'*  Date    : 2008-02-13                                        *
'*  Version : 2008-02-16                                        *
'*  Notes   : PIC16F872 @ 20 MHz                                *
'*                                                              *                                                              *
'*                                                              *
'****************************************************************
</i></font>ADCON1 = <font color="#808080">7 </font><font color="#008000"><i>' Alla digitala
</i></font><font color="#000080">DEFINE </font>OSC <font color="#808080">20
</font><font color="#000080">DEFINE </font>LCD_COMMANDUS <font color="#808080">3000   </font><font color="#008000"><i>'Set command delay time in us
</i></font><font color="#000080">DEFINE </font>LCD_DATAUS <font color="#808080">200       </font><font color="#008000"><i>'Set data delay time in us
</i></font><font color="#000080">DEFINE </font>DEBUG_BAUD <font color="#808080">2400 
</font><font color="#000080">DEFINE </font>DEBUG_MODE <font color="#808080">0
</font><font color="#000080">DEFINE </font>DEBUG_REG PORTC
<font color="#000080">DEFINE </font>DEBUG_BIT <font color="#808080">7   </font><font color="#008000"><i>'PORTC.7 OLIMEX RS232Board
</i></font><font color="#000080">INCLUDE </font><font color="#FF0000">&quot;modedefs.bas&quot;
</font>ReciverPIN <font color="#000080">VAR </font>PORTC.<font color="#808080">0
</font>Check1 <font color="#000080">VAR BYTE
</font>Check2 <font color="#000080">VAR BYTE
</font>Counter <font color="#000080">VAR BYTE
</font>Errors <font color="#000080">VAR WORD


CLEAR
PAUSE </font><font color="#808080">500
</font><font color="#000080">LCDOUT </font><font color="#808080">$FE</font>,<font color="#808080">1

</font>Main:
    <font color="#000080">SERIN </font>ReciverPIN,N2400,<font color="#808080">100</font>,NoSignal,[<font color="#808080">$55</font>,<font color="#808080">$55</font>,<font color="#808080">$55</font>,<font color="#808080">63519</font>],Counter,Check1,Check2
    
    <font color="#000080">IF </font>Check1 = <font color="#808080">121 </font><font color="#000080">AND </font>Check2 = <font color="#808080">212 </font><font color="#000080">THEN 
        GOSUB </font>LCD
    <font color="#000080">ELSE
       GOSUB </font>NoSignal
    <font color="#000080">ENDIF
        
GOTO </font>Main

LCD:
    <font color="#000080">LCDOUT </font><font color="#808080">$FE</font>,<font color="#808080">$80</font>, #Counter, <font color="#FF0000">&quot;    &quot;
    </font><font color="#000080">DEBUG </font>#Counter, <font color="#808080">13</font>,<font color="#808080">10    
    </font>Check1 = <font color="#808080">0  
    </font>Check2 = <font color="#808080">0
</font><font color="#000080">GOTO </font>Main

NoSignal:
    Errors = Errors + <font color="#808080">1

    </font><font color="#000080">LCDOUT </font><font color="#808080">$FE</font>,<font color="#808080">$C0</font>, <font color="#FF0000">&quot;ERROR:&quot;</font>,#Errors,<font color="#FF0000">&quot; &quot;</font>,#Check1,<font color="#FF0000">&quot; &quot;</font>,#Check2
    <font color="#000080">DEBUG </font>#Counter, <font color="#FF0000">&quot;ERROR:&quot;</font>,#Errors,<font color="#FF0000">&quot; &quot;</font>,#Check1,<font color="#FF0000">&quot; &quot;</font>,#Check2, <font color="#808080">13</font>,<font color="#808080">10
    </font>Check1 = <font color="#808080">0
    </font>Check2 = <font color="#808080">0 
</font><font color="#000080">GOTO </font>Main
<font color="#000080">END 
</font></code></pre><!--EndFragment--></body>
</html>

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