Problem with wireless link between receiver and transmitter

antenna problem

I want to transmitt some digital data wirelessely uptill a distance of about 10 meters.For this purpose I am using a mcu and RF modules from Linx technologies
TXM-418-LC and RXM-418-LC.These are receiver and transmitter modules respectively.i am using a planar antena by the same manufacturer called SPLATCH

Now poblem is when the transmitter and receivers are at a distance of around less than 3 feet i have reliable wireless link but as the distance increases
the quality of link becomes bad and bad(By quality i mean i start getting garbage data at higher distances)

Also when the distance is increased the performance of wireless link varies with the surroundings meaning as i will start moving between the link some times link becomes good and at the movement of some ponts it becomes bad.

I personally think that this problem is due to antenna
Any views why this is happening ? and if this is due to antenna problem some one Please guide me in making this antenna efficient or to design a new antenna by my self as i am very new to this RF field.

I some where read that a simple piece of wire can be used as antenna if we can calculate its required length if this is true help me in this regard

Please have a look at the datasheets of RF modules at the following links:

**broken link removed**

**broken link removed**


Plz note that i have not made PCB for using these RF modules i have mounted the modules and antenna on vero boards this may be a problem

antenna problem

The page 13 of the TXM data sheet mention how to calculate the length of the simple piece of wire. The whip antenna mentioned can be just a simple piece of wire. 6.7" is good for 418MHz. Place the two antenna into the same direction can give you the best range.

Re: antenna problem

Munib

You do not have the microwave knowledge I guess.

The impedance match is necessary when connect the module and the antenna.

You do not test it in regular PCB and calculate the trace impedance, I suppose.

Try to find someone major in RF to help you.

Re: antenna problem

oh,this is the question of the system analysis,the reason is the following:

(1) when the TX power is constant, when the data speed increase,then the coverage area is reduced,the reason can be explained as the following equation
Eb/N0=(C/N0)/Rb

the (C/N0)is the carrier noise power spectral ratio,Rb is the data speed rate,so when the transmit power is constant,when y increase the Rb,then Eb/N0 decrease so the coverage decrease;

(2) the multipath effect is the main factor for your second phenomenon

so y can increase your Tx power to get large coverage,it is nothing with the antenna,certainly y can use the directional antenna to increase the coverage in some direction!

Re: antenna problem

Hi,

your problem is indeed at the antenna level,

In an average indoor situation the expected range is in the order of 50 meter assuming: Tx power =0 dbm, RX sensitivity = -95dbm, indoor exponent of 3, and antenna gain of -10 dbi for RX and -10dbi for TX

Try to use antennas with -10 db gain or better and your range will be arround 50 meters,


tony

Re: antenna problem

For your RF module in 418MHz use the yagi antenna 12 element can build by you.

This is geometry of antenna. Use 3mm alumunium as reflector, driven and another element

NOTES Automatically produced by first
FREQUENCY 417.000000
MIN_FREQUENCY 416.000000
MAX_FREQUENCY 418.000000
STEP_FREQUENCY 0.100000
ELEMENTS 12
DRIVEN 1
PARASITIC 11
ANGULAR_STEP 180.000000
#DATA_DRIVEN x y length diameter voltage(r) voltage(i)
DATA_DRIVEN 0.14388 0.00000 0.33480 0.00300 1.00000 0.00000
#DATA_PARASITIC x y length diameter
DATA_PARASITIC
0.00000 0.00000 0.34829 0.00300 reflector
0.19784 0.00000 0.31764 0.00300 D1
0.32734 0.00000 0.31489 0.00300 D2
0.48201 0.00000 0.31161 0.00300 D3
0.66187 0.00000 0.30833 0.00300 D4
0.86331 0.00000 0.30615 0.00300 D5
1.07914 0.00000 0.30342 0.00300 D6
1.30576 0.00000 0.30179 0.00300 D7
1.54317 0.00000 0.29962 0.00300 D8
1.79137 0.00000 0.29853 0.00300 D9
2.05036 0.00000 0.29745 0.00300 D10

This is performance of antenna

# Driven=1 parasitic=11 total-elements=12 design=417.000MHz
# Checked from 416.000MHz to 418.000MHz.
f(MHz) E(deg) H(deg) R jX VSWR Gain(dBi) FB(dB) SideLobes(dB)

416.000 36.9 40.3 40.36 -13.15 1.435 14.041 17.921 0.000
416.100 36.8 40.2 40.54 -13.05 1.428 14.050 17.872 0.000
416.200 36.8 40.2 40.73 -12.96 1.421 14.060 17.822 0.000
416.300 36.8 40.2 40.92 -12.87 1.414 14.069 17.773 0.000
416.400 36.6 40.1 41.11 -12.79 1.407 14.078 17.723 0.000
416.500 36.6 40.1 41.30 -12.71 1.401 14.087 17.673 0.000
416.600 36.6 40.0 41.49 -12.63 1.395 14.096 17.622 0.000
416.700 36.6 40.0 41.69 -12.56 1.389 14.105 17.572 0.000
416.800 36.5 40.0 41.88 -12.49 1.383 14.114 17.521 0.000
416.900 36.5 39.9 42.07 -12.43 1.377 14.123 17.470 0.000
417.000 36.5 39.9 42.26 -12.37 1.372 14.131 17.420 0.000
417.100 36.4 39.8 42.45 -12.32 1.367 14.140 17.369 0.000
417.200 36.4 39.8 42.64 -12.27 1.361 14.148 17.318 0.000
417.300 36.4 39.7 42.84 -12.23 1.357 14.157 17.268 0.000
417.400 36.3 39.7 43.03 -12.19 1.352 14.165 17.217 0.000
417.500 36.3 39.6 43.22 -12.15 1.348 14.173 17.167 0.000
417.600 36.3 39.6 43.41 -12.12 1.343 14.182 17.117 0.000
417.700 36.2 39.6 43.59 -12.10 1.339 14.190 17.067 0.000
417.800 36.2 39.5 43.78 -12.08 1.336 14.198 17.018 0.000
417.900 36.2 39.5 43.97 -12.07 1.332 14.206 16.969 0.000
418.000 36.1 39.4 44.15 -12.06 1.329 14.214 16.920 0.000