I notice that the stock 3DR Radio antennas have a gain of 2dB..
What's the gain(if any) of a plain wire antenna?
I'm looking at a 433 transceiver board RFM22B from Spark Fun. I has a different Si RF chip. It's the Si4432 chip which is strictly a radio transceiver without the embedded microcontroller. My ultimate goal is to build an RC transmitter with an Arduino 2560 as the base.
Latency becomes critical, and in my mind the embedded microcontroller in the Si1000 adds just another level of latency. Plus the microchip core of the Si1000 is that of a 8051 which I don't want to have to learn.
The description from SparkFun of this RFM22B board (Si4432 chip) says that you can use 17cm of wire as your antenna. They really don't specify what kind of wire. I suppose insulated copper wire? Do they mean stranded or single core copper wire? What guage of copper wire?
Anyway, I was just wondering how well this would work? Also what guage and type of wire?
Replies
It's going to be big :p http://www.rcgroups.com/forums/showthread.php?t=1388264 I would almost go with an antenna tracking directional, or buy a amp instead.
I struggled with the analogy using the audio engineering philosophy.. and am glad I deferred. :) Well said all.
With either RF or audio, the ability of the device to radiate efficiently or collect energy well is significant.
Audio discipline suffers more from physical affects due to the transfer medium, i.e. a speaker makes a poor microphone and vice versa.
With RF, the radiating/collecting device has nearly a reciprocal performance function.
When the device is on an object moving in 3 dimensions, radiating/collecting patterns become more important IMHO.
The recent popularity of circular polarization antennae for FPV is one example. At the 2.4GHz band, as Jake mentioned, even slight errors can lead to a poorly performing system.
Another anecdote: My local radio club members tell the story of one old mentor that taught code training classes. The class was in the basement of the local college and did not have an external antenna. Not letting that deter him, the old mentor connected his antenna tuner to the legs of the folding table with gator clips and proceeded to QSO with another fellow across town. This amazed the students who, did not know or understand that the *efficiency* of the ad hoc antenna was probably off the measureable scale.
I will save my EME (moonbounce) experience stories for another discussion.
Note: the average freespace path loss for 1296MHz is 271.1 dB (+/- 1.1 dB for lunar elliptical orbit)
Oh, if you want to poke around an old directory of my Spectrum Analyzer project.. HERE
Thanks guys for the responses. It sounds like there's no magic to this...that a wire 1/4 of the wavelength will more or less work.
I guess it all boils down to what precision you're after.
Which reminds me of a story. Years ago I was interested in building an amplifier for stereo speakers. So I lurked around some of the DIY amplifier and speaker forums. Some of those guys were really hardcore and had speaker systems worth tens of thousands of dollars. But then when the subject of speaker cables came up...all hell broke loose!!!
You've seen those thick monster cables they sell...all in the name of sound quality. Well I guess you can actually spend thousands of dollars for such cables. The vendors could show on oscilloscopes(or whatever instrument) how much better their cables were than the competition's.
One of the hardcore guys called it the biggest scam in the hi-fi industry. He claimed that no matter how good you thought your ears were, he could solder together coat hangers and connect them up to your $10,000 set of speakers...and you couldn't tell the difference. This went back and forth, as some of his friends had ponyed up big bucks for cables. So finally they took him up on his challenge. They invited him over to their homes to conduct a "double-blind" test on their own systems.
Well, you can guess what happened.
Consistently, none of them could identify which was which.
It just goes to show, regardless of what the osillloscopes(etc.) said, the precision of the human ear was in no way capable of making any distinction.
If one *really* wants to split hairs, the perfect RF conductor is tubular because all the rf energy travels on the surface of a conductor due to skin effect. High power RF sites use tubular coax to handle the power. Not needed in this case.
Antenna Gain Wiki
Skin Effect Wiki
I wouldn't go buy wire but use what you have that is appropriately sized for the circuitry. Unless you get beyond a substantial portion of a wavelength, stranded wire works just fine BUT if you are needing a cheap, solid antenna, solid wire is better. You could not measure the difference without a $25,0000 network analyzer and maybe not even with that.
I built a spectrum analyzer for my senior project. Part of the design was a rework of another unit to move it into a higher band. 30MHz max moved to 148MHz max. The hardest part of the RF was was tuning a 5 element interdigital filter I built from scratch. It looked something like THIS filter (but mine was in aluminum, machined).
Even after all the calculations, measuring twice, cutting once, painstaking studying - it did not work.
Another hobby friend, also an amateur radio astronomer like myself, worked at a neat place near where I lived and had a network analyzer I could use. About 7 hours later and multiple trips to a bench with a hacksaw, the filter worked great.
In short, study a bit, cut and hack until it works. You could just save yourself the trouble and buy an antenna... unless you are looking for college credit like I was. ;)
A half-wavelength dipole antenna can get 2.15dBi. The stock antennas are just regular wire antennas set in plastic. They'll perform no better or worse than a regular wire antenna.
You would want to use a solid core copper wire for the antenna. A common way to do things is simply strip the proper length of shielding off one end of a coax cable. Using stranded wire you won't be able to get the proper length on all the wires and you'll detune your antenna.
Antenna gain dBi is specified in relation to a theoretical isotropic radiator.
As far as using the Si4432... I have no idea why you'd want to do this. The HopeRF module used in the 3DR radios is $10 and the Si100X chip only costs about $1-2 more than the Si4432. For that you get a nice processor and firmware that's already written.
Spending months writing custom firmware just to end up burning up a lot of cycles on your main processor sounds like a bad idea. You should double check if you even have the processing power to do this first. There's a lot of processor overhead involved if you want anything more than the most basic implementation.
The Si100X has more processing power than the APM, so if you're thinking of trying to run the Si4432 from the APM or another Audrino platform it probably isn't going to happen.
Gain is always in reference to something else...in this case probably a dipole antenna at the same frequency but.. that is not stated. In any case 3 dB is twice (or half) as compared to something else. Specifying gain is meaningless without a reference.
The 'plain wire' antenna is also not so simple. A 1/4 wave (at a specified frequency) vertical antenna is simple. The 17cm antenna you mention above would probably be considered a 'long wire' antenna. HERE is an article that uses 433 MHz in the discussion. It discusses 1/4 wave and dipoles. I suspect insulated stranded wire about 22 - 26 gauge would be fine. It needs to be flexible (single conductor is usually not flexible).
The antennas that simply screw/plug onto the RF boards are usually considered 'rubber ducky' type and are technically a special case of a helical antenna.
I don't know if this helps your question or not but at least you have more information to work with.