Hello,
I have bought a pair of 434 Mhz Radio Transmitter and Emitter http://www.sparkfun.com/datasheets/RF/KLP_Walkthrough.pdf and am looking for some ideas regarding the best type of antenna. Could anyone please help me? 
am looking for some ideas regarding the best type of antenna.
The best antenna would be one connected to a better radio. Those are cheap radios subject to all kinds of interference with no integrity checking of the data sent and no retries.
PaulS:
The best antenna would be one connected to a better radio.
434 MHz radios generally just need a piece of 17 cm wire. I have used something as simple as a piece of 30 guage wirewrap wire just hanging loose in my plastic housing on both ends.
Those kind of Rx/Tx pairs work well with Virtualwire, which will take care of encoding the message for you and send up to 27 bytes at at time at speeds to 2000 bits/second.
You could also google it and find this:
A dipole is two side -- so that would be twice as long -- cut in the middle and fed to coax or twin lead.
I used "One Side" on that screen -- which tells you how long to make a Vertical "Ship antenna" -- which is just 1/2 a dipole.
So the answer of 17cm is pretty close. Start there and maybe play with a couple of antennas -- trimming them to see if they work better.
How do you do that? Find that distance apart at which you can communicate -- but with difficulty. Shorten the antennas slightly -- test for improvement -- if you see improvement shorten some more.
If it gets worse -- you need longer antennas -- start over. Sorry about that -- try 18cm -- then shorten as per above instructions.
Wiki has a reasonable answer --
See frequency vs length -- remember that is a dipole formula cut in half for a "whip".
l= 143/f (meters) or l = 468/f (feet)
WillR:
How do you do that? Find that distance apart at which you can communicate -- but with difficulty. Shorten the antennas slightly -- test for improvement -- if you see improvement shorten some more.If it gets worse -- you need longer antennas -- start over. Sorry about that -- try 18cm -- then shorten as per above instructions.
No this is not quite right. The antenna needs to resonate. The 17cm length is approximately 1/4 of the wave length of the frequency in use. The antenna should be cut for the frequency being used. If a 1/4 wave whip is not sufficient, then you can add a ground plane. The ground plane would be a few wires at right angles to the whip and 20% longer. Someone mentioned a dipole. That's two legs, each 1/4 wave long, one fed from the center fo the feed line and the other connected to the braid. These are directional, with signal radiated off their sides.
If this is not adequate, you can build more complex directional antennas.
skyjumper:
WillR:
How do you do that? Find that distance apart at which you can communicate -- but with difficulty. Shorten the antennas slightly -- test for improvement -- if you see improvement shorten some more.If it gets worse -- you need longer antennas -- start over. Sorry about that -- try 18cm -- then shorten as per above instructions.
No this is not quite right. The antenna needs to resonate. The 17cm length is approximately 1/4 of the wave length of the frequency in use. The antenna should be cut for the frequency being used. If a 1/4 wave whip is not sufficient, then you can add a ground plane. The ground plane would be a few wires at right angles to the whip and 20% longer. Someone mentioned a dipole. That's two legs, each 1/4 wave long, one fed from the center fo the feed line and the other connected to the braid. These are directional, with signal radiated off their sides.
If this is not adequate, you can build more complex directional antennas.
One could say that anything is not quite right. ]
Amirra is an engineering student. She rarely asks a second question in any area. She can read and figure things out for herself. Never ever give an engineering student too much information -- they take great pride in their ability to figure out things that don't yet know.
I pointed her to places that would fill in all the details I left out and that everyone else left out.
So... Those radios are never quite on the the freq. you expect. One would think if shortening the antenna does not work -- lengthening might work. However un-cutting the wire is not that easy -- starting over again with a piece "too long" seemed simpler to me.
I do think I got it right -- but I did get a chuckle.
You made my day.
Well there are other people reading the thread besides the OP. As for your rather arrogant and condescending comments, I'm not quite sure I see your point. People ask for help, and if we're giving them help it should be actually helpful.
Along those lines, transmitting antennas don't work if they don't resonate. Period. If they don't, they reflect power back into the transmitter rather than put it to good use. You can't just shove a longer piece of wire into a transmitter and expect it to work better. Or a shorter one.
If your point was to find the proper length by trial and error, well how do you know that the problem, if there is one, lies with the antenna? There are many problems that can happen when two radios are trying to communicate. Randomly guessing that an antenna is too short or too long is of little value. Besides, the antenna length can be calculated. Radios don't just spit out energy wherever they please. If they did, the receiver would have no hope of receiving. Cut the antenna for the center of the frequency range of the transmitter and be done with it.
Appreciate the thoughts.
Whatever antenna one decides to use, is there a way to fine-tune it to compensate for measurement errors and other sources of error? How can one know whether the antenna resonates properly?
Sparkfun also sells what appears to be a better quality 433-Mhz transceiver.
Anyone used this? Jeenode uses a similar device, but lower transmit power.
Whatever antenna one decides to use, is there a way to fine-tune it to compensate for measurement errors and other sources of error? How can one know whether the antenna resonates properly?
To do this you need decent Radio Frequency Test Equipment.
As mentioned, an antenna that is not resonant at or near the operating frequency reflects some of the power back to the transmitter. Instruments to measure this are:
- A "Standing Wave Ratio" or SWR meter. A well matched resonant antenna will have a SWR of close to 1
- An RF power meter that can measure forward and reflected power.
Both of these require the transmitter to be operating.
-or- - An "RF Noise Bridge" or "Antenna Analyzer" which operate without the usual transmitter and provide their own signals.
BUT, "It's Complicated":
(1) Mostly because most of the active SWR or Power meters are designed for powers of 1 watt to 1000 watts, and these small transmitters probably are too low in power to indicate well or at all. An Amateur Radio UHF (typically 440 Mhz) SWR or Power meter is the easiest to find instrument in this frequency range.
(2) Even if a noise bridge or antenna analyzer have helped you tune an antenna well, this all assumes that the operating impedance of the transmitter, coax/transmission line and antenna are the same. Probably 50 ohms. Approximately.
With typical commercial or amateur radio transmitter of a few watts power and more, there are typically tuning adjustments in the transmitter output stage to tune and match the transmitter to the load presented by the antenna and transmission line.
Really accurate measurements of antennas are a science and somewhat of an art, and require a "antenna range" to set up transmission paths that are repeatable.
However: For simple short-range communications, an "almost right" antenna will probably work "OK". Technically speaking.
The simplest sort-of-instrument is a "field strength meter" or a calibrated receiver which can display "received signal strength. You need to set up an uncluttered repeatable 'near field' path of perhaps 1 to 10 meters distance where you can see a received signal indication. Then keeping everything else the same, try different antenna lengths, tuning (if there is any adjustment) etc. This is just a "relative better-worse" measurement but it's approachable.
I'm about to do some antenna / operating range testing on 300 Mhz "X-10" RF remote controls in the next couple of weeks and will have all of the above challenges.
I used to do Broadcast Engineering where this was about high-power AM systems (About 1 Mhz) at 1000 to 50,000 watts and tower-size antennas, and 500 to 10,000 watt FM systems (about 100 Mhz) with multiple-element antennas mounted up on high towers where you didn't want to be out tuning stuff But we had good instruments and a budget.
Let us know what you find out.
terryking228:
To do this you need decent Radio Frequency Test Equipment.
I have a SWR bridge, but it's designed for the range 87-109MHz (this is according to the manufacturer's specification, but I guess it would work just a bit off this range of freqs - but not at 433MHz and not at that low power as my board produces.) In that case, I guess I'll have to go through some trial-and-error and see if I can optimise the length of my antenna.
The common receiver circuit board RWS-371 is compatible with Arduino and comes with a signal strength indicator. I'll use that and see what I can get. Thanks a lot for the answer! (I'll let you know about the outcome).