Author Topic: RF transmission help required  (Read 1665 times)

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Offline aruna1Topic starter

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RF transmission help required
« on: August 19, 2011, 09:18:32 AM »
Hi
I'm using following RF transmitter and receiver in my final year project. frequency is 434 MHz

Project is about ultrasonic based localization where we use multiple wall mounted ultrasonic receiver systems.

Each Ultrasonic receiver system contains RF transmitter and a RF receiver. SO Ultrasonic receiver systems can communicate with each other.

Transmitter:
http://www.szsaw.com/En/html/product.asp?id=379

Receiver:
http://www.szsaw.com/En/html/product.asp?id=344

According to data given they should work about 100m.

but my problem is I cant use them to send data reliably more than 2m . :( Data get corrupted due to lot of noise.(checked with an oscilloscope) if range is more than 2m.

I believe problem is with antennas.

I'm using 30cm long circuit wires for antennas (lambda/2). and I found transmission is possible only if these wires are allowed to hang freely outside the enclosure (plastic). this is a big problem. I need to make a compact system so hanging wires are not an option. It is okey if I can wind the wires and put them in side the enclosure, but if i do so transmission range drops to  20-30cm. :(

I did some readings and found monopole antennas need large ground planes, which is not available to me. Actually any size of ground plane is not available in the design.

I'm powering up the system with 230AC mains (reduced and regulated using a transformer and 7809/7805).

Transmitter is powered with 9V. (7809) receiver is powered with 5V.

I'm not using any encoder/decoder chip. I'm using PIC12F683 to decode the data.
Data contains  4 start bits + 5 address bits + 11 data bits + 4 end bits.

bit length is 1ms. so transmission speed is 1kbps.

Any idea on how to increase the range up to at least 10m ?

and is there anyway to use single antenna for both transmitter and receiver?
Thank you

EDIT:

Is it possible to get better transmission using following modules? they work in 2.4GHz range and environment I work has a WIFI network.So I believe WIFI network will interfere with these transceivers.

http://www.ebay.com/itm/RF-2400P-Wireless-Transceiver-Module-2-4G-RF-Module-/320715876578?pt=LH_DefaultDomain_0&hash=item4aac27e8e2

http://www.ebay.com/itm/Leatest-2-4Ghz-nRF24L01-RF-Transceiver-Module-ISM-/280576538540?pt=LH_DefaultDomain_0&hash=item4153aa37ac

I'm running out of options, so if above transceiver units will help to solve my problem, I should order them asap. So I'm waiting for your advice.
« Last Edit: August 19, 2011, 09:50:21 AM by aruna1 »
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Offline aruna1Topic starter

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Re: RF transmission help required
« Reply #2 on: August 19, 2011, 09:37:32 PM »
thanks billhowl  :)
I'll go through links you provided and get back to you. :)
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Offline aruna1Topic starter

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Re: RF transmission help required
« Reply #3 on: August 19, 2011, 11:33:15 PM »
Quote
You should use lambda/4f about 17cm.


I read somewhere (in internet) that (lambda/2) is better than (lambda/2)

Quote
you can loop antenna on PCB
Antenna App Note: Part I Loop Antennas


I have already read "Antennas for Low Power Applications " by RFm
http://www.rfm.com/products/apnotes/antenna.pdf

according to that loop antenna has to be tuned using a capacitor and is not easy and I dont know how to do it.

Quote
or this antenna


I'm looking fr method to hide the antenna plus I don't have access to this kind of antennas.(frequency). ordering them from another country takes too long.


Question about the PCB antenna is, I have to use a separate PCB as a antenna, because RF module only has a hole to solder a wire. So is it possible to print a antenna pattern (loop or any other methods mentioned in antenna.pdf) and connect that antenna PCB to RF unit using a wire.

If this is possible it will be much easy. I believe PCB antennas does not require ground planes.

and how to connect this PCB to RF unit? what kind of wire should I use? coaxial maybe? if coaxial is suitable, how to connect wires? I mean center wire is used to connect RF unit to PCB, so where does the wire mesh of coaxial connect?

thank you

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